COSEWIC Assessment and Status Report on the Nuttall's Sheep Moth Hemileuca nuttalli in Canada - 2015

Photo of Nuttall's Sheep Moth
Photo: Nuttall's Sheep Moth

Endangered
2015

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Document Information

COSEWIC
Committee on the Status
of Endangered Wildlife
in Canada

COSEWIC logo

COSEPAC
Comité sur la situation
des espèces en péril
au Cananda

COSEWIC status reports are working documents used in assigning the status of wildlife species suspected of being at risk. This report may be cited as follows:

COSEWIC. 2015. COSEWIC assessment and status report on the Nuttall's Sheep Moth Hemileuca nuttalli in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. x + 41 pp. (Species at Risk Public Registry website).

Production note:

COSEWIC would like to acknowledge Allan Harris and Rob Foster for writing the status report on the Nuttall’s Sheep Moth (Hemileuca nuttalli), in Canada, prepared under contract with Environment Canada. This status report was overseen and edited by Jennifer Heron, Co-chair of the COSEWIC Arthropods Specialist Subcommittee.

For additional copies contact:

COSEWIC Secretariat
c/o Canadian Wildlife Service
Environment and Climate Change Canada
Ottawa, ON
K1A 0H3Tel.: 819-938-4125
Fax: 819-938-3984
E-mail: COSEWIC E-mail
Website: COSEWIC

Également disponible en français sous le titre Ếvaluation et Rapport de situation du COSEPAC sur L'hémileucin de Nuttall (Hemileuca nuttalli) au Canada.

Cover illustration/photo:

Nuttall's Sheep Moth -- Photo provided by author.

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COSEWIC Assessment Summary

Assessment Summary – November 2015

Common name
Nuttall's Sheep Moth
Scientific name
Hemileuca nuttalli
Status
Endangered
Reason for designation
This large, showy and conspicuous moth is restricted to Antelope-brush habitat in the Okanagan Valley of British Columbia. That habitat type has declined considerably in quality and extent in the past century and remains under threat due to continued conversion to viticulture, residential and commercial development, and impact of wildfires. This is a rare moth in Canada: very few have been observed since the first record in 1920. Potentially large fluctuations in the population size may affect its long-term viability.
Occurrence
British Columbia
Status history
Designated Endangered in November 2015.

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COSEWIC Executive Summary

Nuttall's Sheep Moth - Hemileuca nuttalli

Wildlife Species Description and Significance

Nuttall's Sheep Moths (Hemileuca nuttalli) are large members of the wild or giant silk moth family (Saturniidae). Adults of both sexes have forewing lengths of 32-39 mm with white to pale yellow forewings and bright yellow hindwings framed by a pattern of thick black markings. Larvae are spiny and black, with the final instars approximately 50 mm in length.

Distribution

The global range of Nuttall’s Sheep Moth is from the extreme southern portion of the Okanagan Valley in British Columbia, southward to northern Arizona and New Mexico. In Canada, it has been recorded from the south Okanagan Valley from three general areas: 1) Osoyoos, 2) Oliver (precise site unknown), and 3) Vaseux Lake. The most recent records for the species are 2002 near Vaseux Lake and 1986 at Haynes’ Lease Ecological Reserve (approximately 8 km north of Osoyoos). It is unknown if the Haynes’ Lease occurrence is the same location as historical records labelled ‘Osoyoos’ and the precise location of the Oliver record is unknown. Targeted surveys for adults at six sites in 2009 and for larvae at 16 sites in 2014 were unsuccessful. The targeted searches in 2014 included the 2002 site.

Habitat

In Canada, Nuttall’s Sheep Moth is found in the bunchgrass shrub-steppe on dry, open slopes at low elevations where the only known Canadian larval host plant, Antelope-brush (Purshia tridentata), is most abundant. The main habitat is the Antelope-brush/Needle and Thread Grass plant community, which is fragmented by habitat loss; less than 33% of its historical mapped distribution remains in approximately 3200 ha in the Okanagan Valley.

Biology

Nuttall’s Sheep Moth is univoltine and may have a life cycle that spans 1 – 2 years. The eggs are laid on the host plants in late summer and overwinter, typically hatching in late April or May the following spring. Early instar larvae are gregarious, while later instar larvae are solitary. The 5th instar larva creates a cocoon in leaf litter or a shallow burrow, and the adult emerges later that season or possibly the following year. In Canada, the known flight period is August through early September, although individual moths have shorter life spans (adults do not feed). Adults are diurnal with a peak of activity in the afternoon, and both sexes are rapid, fast fliers. Perched females emit pheromones to attract potential mates.

Population Size and Trends

There is insufficient information to determine Nuttall’s Sheep Moth population sizes or trends. Thousands of larvae were observed near Vaseux Lake in 1976, and the species was last observed there in 2002. Nuttall’s Sheep Moth was last observed at Haynes’ Lease in 1986 despite repeated surveys. No population trend data are available but apparently suitable Antelope-brush habitat in the Okanagan Valley has significantly declined in quality, area and extent.

Threats and Limiting Factors

Cumulative habitat loss, degradation, and fragmentation from agriculture (mainly vineyards and orchards) as well as residential and commercial development are the most significant threats to Nuttall’s Sheep Moth populations in Canada.

Protection, Status, and Ranks

Nuttall’s Sheep Moths have no formal protection or status in Canada. It is not ranked by the BC Conservation Data Centre and is considered globally secure.

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Technical Summary

Scientific Name:
Hemileuca nuttalli
English Name:
Nuttall's Sheep Moth
French Name:
Hémileucin de Nuttall
Range of occurrence in Canada (province/territory/ocean): :
British Columbia

Demographic Information

Demographic Information of the species
Summary ItemsInformation
Generation1-2 years
Is there an [observed, inferred, or projected] continuing decline in number of mature individuals?Yes. Inferred due to loss of Antelope-brush habitat
Estimated percent of continuing decline in total number of mature individuals within [5 years or 2 generations]Unknown
[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the last [10 years, or 3 generations].Unknown
[Projected or suspected] percent [reduction or increase] in total number of mature individuals over the next [10 years, or 3 generations].Unknown
[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over any [10 years, or 3 generations] period, over a time period including both the past and the future.Unknown

Are the causes of the decline a)clearly reversible and b) understood and c) ceased?

  • Decline is inferred through habitat loss; it is not easily reversible and is not ceased.
  1. No
  2. Yes
  3. No

Are there extreme fluctuations in number of mature individuals?

  • Historical and recent records have not been abundant. However, observations of hundreds of larvae suggest the possibility of large adult abundance.
probable

Extent and Occupancy Information

Extent and Occupancy Information of the species
Summary ItemsInformation
Estimated extent of occurrence71 km²
Index of area of occupancy (IAO) (Always report 2x2 grid value).20 km²
Is the population "severely fragmented" ie. is >50% of its total area of occupancy in habitat patches that are (a) smaller than would be required to support a viable population, and (b) separated from other habitat patches by a distance larger than the species can be expected to disperse?
  1. No
  2. No
Number of locations (use plausible range to reflect uncertainty if appropriate)
(Note: See Definitions and Abbreviations on COSEWIC website and IUCN (Feb 2014) for more information on this term.)
< 5
Is there an [observed, inferred, or projected] decline in extent of occurrence?Yes, inferred based on loss of the host plant Antelope-brush
Is there an [observed, inferred, or projected] decline in index of area of occupancy?Yes, inferred based on loss of the host plant Antelope-brush
Is there an [observed, inferred, or projected] decline in number of subpopulations?Yes, inferred based on loss of the host plant Antelope-brush
Is there an [observed, inferred, or projected] decline in number of "locations"?
(Note: See Definitions and Abbreviations on COSEWIC website and IUCN (Feb 2014) for more information on this term.)
Yes, inferred based on loss of the host plant Antelope-brush
Is there an [observed, inferred, or projected] decline in [area, extent and/or quality] of habitat?Yes, inferred decline in habitat area and quality.
Are there extreme fluctuations in number of subpopulations?No
Are there extreme fluctuations in number of "locations"?
(Note: See Definitions and Abbreviations on COSEWIC website and IUCN (Feb 2014) for more information on this term.)
No
Are there extreme fluctuations in extent of occurrence?No
Are there extreme fluctuations in index of area of occupancy?No

Number of Mature Individuals (in each subpopulation)

Number of Mature Individuals of the species
PopulationN Clones (index of Mature Individuals)
TotalUnknown

Quantitative Analysis

Quantitative Analysis of the species
Summary ItemsInformation
Probability of extinction in the wild is at least [20% within 20 years or 5 generations, or 10% within 100 years].None.

Threats (actual or imminent, to populations or habitats, from highest impact to least)

The cumulative loss, degradation, and fragmentation of the Antelope-brush ecosystem are the primary threats to Nuttall’s Sheep Moth. The ecological integrity and condition of Antelope-brush grasslands have been severely reduced. Threats include fragmentation by

  • agricultural development (particularly vineyard),
  • urban/suburban development,
  • alteration to fire regimes and the resultant high intensity wildfires at some sites,
  • overgrazing from domestic livestock,
  • spread and continued introduction of invasive non-native plants.

Rescue Effect (immigration from outside Canada)

Rescue Effect of the species
Summary ItemsInformation
Status of outside population(s) most likely to provide immigrants to Canada.Washington State populations are apparently stable.
Is immigration known or possible?Unknown. Adults are capable of flight and nearest known Washington population is approximately 100 km from nearest potentially suitable habitat in Canada. However, it is unlikely, because they are habitat-specific, do not feed as adults and not known for long-distance movements.
Would immigrants be adapted to survive in Canada?Yes. Northern Washington has similar climate and vegetation as the southern Okanagan Valley.
Is there sufficient habitat for immigrants in Canada?Yes. Apparently suitable habitat appears to be currently unoccupied, including at some historical sites in the Okanagan Valley.
Are conditions deteriorating in Canada?
See Table 3 (Guidelines for modifying status assessment based on rescue effect)
Yes. Habitat is being lost through conversion to other land use practices such as vineyards and residential development.
Are conditions for the source population deteriorating
See Table 3 (Guidelines for modifying status assessment based on rescue effect)
Yes, but land development pressures in northern Washington are less severe than in southern B.C.
Is the Canadian population considered to be a sink?
See Table 3 (Guidelines for modifying status assessment based on rescue effect)
No. Nuttall's Sheep Moth has persisted in Canada for over 100 years and is assumed self-sustaining because there is no evidence of regular movements of large numbers of individuals from Washington state.
Is rescue from outside populations likely?Not likely. Adults do not feed and it is unlikely they would expend energy to disperse long distances.

Data-Sensitive Species

Data-Sensitive information of the species
Summary ItemsInformation
Is this a data sensitive species?No.

Status History

COSEWIC: COSEWIC: Designated Endangered in November 2015.

Status and Reasons for Designation:

Status:
Endangered
Alpha-numeric code:
B1ab(iii)c(iv)+2ab(iii)c(iv)
Reasons for designation:
This large, showy and conspicuous moth is restricted to Antelope-brush habitat in the Okanagan Valley of British Columbia. That habitat type has declined considerably in quality and extent in the past century and remains under threat due to continued conversion to viticulture, residential and commercial development, and impact of wildfires. This is a rare moth in Canada: very few have been observed since the first record in 1920. Potentially large fluctuations in the population size may affect its long-term viability.

Applicability of Criteria

Criterion A (Decline in Total Number of Mature Individuals):
Not applicable. There are no data to support declines
Criterion B (Small Distribution Range and Decline or Fluctuation):
Meets Endangered B1ab(iii)c(iv)+2ab(iii)c(iv) since the EOO and IAO are both below the threshold (71 km² and 20 km², respectively); meets sub-criterion "a" since there are fewer than 5 locations; meets sub-criterion "b" since there is a continuing decline in the (iii) area, extent and quality of habitat due to continued development and fragmentation of Antelope-brush ecosystems throughout BC; meets sub-criterion "c(iv)" as populations appear to undergo extreme fluctuations based on observations of large numbers of larvae, and large numbers of pupae that will then diapause within the ground for multiple years, and the possibility of wildfire that could cause all pupae to perish and result in their extirpation at a location.
Criterion C (Small and Declining Number of Mature Individuals):
Not applicable. Population size and rates of decline unknown.X
Criterion D (Very Small or Restricted Population):
Not applicable. Population numbers unknown
Criterion E(Quantitative Analysis):
Not applicable. No data available.

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COSEWIC Logo

COSEWIC History

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC Membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.

Definitions (2015)

Wildlife Species
A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.
Extinct (X)
A wildlife species that no longer exists.
Extirpated (XT)
A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.
Endangered (E)
A wildlife species facing imminent extirpation or extinction.
Threatened (T)
A wildlife species likely to become endangered if limiting factors are not reversed.
Special Concern (SC)
(Note: Formerly described as "Vulnerable" from 1990 to 1999, or "Rare" prior to 1990.)
A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.
Not at Risk (NAR)
(Note: Formerly described as "Not In Any Category", or "No Designation Required.")
A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.
Data Deficient (DD)
(Note: Formerly described as "Indeterminate" from 1994 to 1999 or "ISIBD" [insufficient scientific information on which to base a designation] prior to 1994. Definition of the [DD] category revised in 2006.)
A category that applies when the available information is insufficient (a) to resolve a species' eligibility for assessment or (b) to permit an assessment of the species' risk of extinction.

The Canadian Wildlife Service, Environment and Climate Change Canada, provides full administrative and financial support to the COSEWIC Secretariat.

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Wildlife Species Description and Significance

Name and Classification

Order:
Lepidoptera - butterflies and moths
Superfamily:
Bombycoidea
Family:
Saturniidae Boisduval, 1837 – wild or giant silk moths
Subfamily:
Hemileucinae Walker, 1855 - buck, sheepmoths
Genus:
Hemileuca Walker, 1855
Species:
Hemileuca nuttalli (Strecker 1875)
Type locality:
Rocky Mountains, head of Snake River.
Taxonomic Background:
Hemileuca is a diverse genus of silk moths, with 16 of the 20 described species found in western North America (Powell and Opler 2009). Nuttall's Sheep Moth (Hemileuca nuttalli) was first described by Strecker in 1875 (Strecker 1872-1877) as Pseudohazis nuttalli, and was long confused with the Western or Elegant Sheep Moth (Hemileuca eglanterina) (Boisduval 1852), until Ferguson (1971) clearly defined the diagnostic differences between these two species. Under experimental conditions, male Nuttall's Sheep Moths will sometimes mate with female Western Sheep Moths, but no viable embryos are produced (Collins and Tuskes 1979). A colour morph associated with high elevations was described as the subspecies Hemileuca nuttalli uniformis (Cockerell 1914) but has been reduced to a synonymy (Tuskes et al. 1996).
English Names:
Nuttall's Sheepmoth (e.g., Opler et al. 2014) or Nuttall's Buck Moth (e.g., Young and Marks 2009). The species was named after Thomas Nuttall, an English zoologist and botanist who collected in western North America in the early 1800s
French Name:
Hémileucin de Nuttall

Morphological Description

Nuttall's Sheep Moth has four developmental stages: egg, larva, pupa and adult.

Adult:

Nuttall’s Sheep Moth adults are relatively large (forewing length 32-39 mm for both sexes) moths with white to pale yellow forewings and bright yellow hindwings, thick black transverse lines (medial and post-medial), black veins near the wing margins, black wing edges, and very large discal spots on both wings (Figure 1; Crabo et al. 2012). Both sexes have similar maculation and ground colour, although females tend to have more yellow on the dorsal forewing than males, especially distal to the postmedial line (Tuskes et al. 1996). The body is yellow and the antennae are bipectinate, much wider in males than in females.

Figure 1. Adult male Nuttall's Sheep Moth (Benton County, WA.
Photo of Adult male Nuttall's Sheep Moth
Photo Merrill A. Peterson photo, with permission).
Long description for Figure 1

Photo of an adult Nuttall's Sheep Moth, with wings extended. These moths have white to pale yellow forewings and bright yellow hindwings, with thick black transverse lines (medial and post-medial), black veins near the wing margins, black wing edges, and very large discal spots on both wings. The body is yellow and the antennae are bipectinate.

Two other species of Hemileuca co-occur with Nuttall’s Sheep Moth. Western Sheep Moth has pink-suffused forewings and typically has heavier black maculation, although the form “denuda” lacks these markings entirely. Nuttall’s Sheep Moth is distinguished from Western Sheep Moth by the inwardly concave shape of the black postmedial line on the hindwing between vein M3 and the inner margin of the wing (it is straight or outwardly convex in Western Sheep Moth) (Tuskes et al. 1996). Co-occurring Hera or Sagebrush Buck Moth (H. hera) adults are white with black markings.

Egg:

Nuttall’s Sheep Moth eggs are oval and whitish-grey (Ife pers. comm. 2014).

Larva:

Early larval instars are black with stinging spines (McFarland 1974) and are superficially similar to nymphalid butterfly larvae. However, the uppermost dorsal rows of tubercles (scoli) of Hemileuca larvae are shorter than those of the subdorsal rows, and lack the large, conspicuous elongated central shaft found in nymphalids (Ferguson 1971). Late instar larvae of Nuttall’s Sheep Moth (Figure 2)are variable in colour (Tuskes et al.1996), and are difficult to distinguish from other co-occurring Hemileuca larvae (St. John 2010). In southern B.C., late larval instars lack the longitudinal white line and orange-yellow tufts of dorsal spines that are found on Western Sheep Moth and Hera Buck Moth (Ife pers. comm. 2014; St. John 2010). Final instar Nuttall’s Sheep Moth larvae have 6-10 setae on the clypeus compared to only 4 in the other two Hemileuca species found in B.C, and there can also be differences in the colour of the ventral abdominal surface and prolegs (Tuskes 1976). Final instar larvae are over 50 mm long with a head capsule width of just under four mm (St. John 2010).

Figure 2. Late instar larva on Nuttall's Sheep Moth on Antelope-brush (Purshia tridentata)
Photo of Late instar larva on Nuttall's Sheep Moth
(Photo Steve Ife, with permission).
Long description for Figure 2

Photo of a late instar larva of a Nuttall's Sheep Moth, lateral view. Late instar larvae are variable in colour and difficult to distinguish from other co-occurring Hemileuca larvae. The individual shown is black. In southern British Columbia, late larval instars lack the longitudinal white line and orange-yellow tufts of dorsal spines that are found on Western Sheep Moth and Hera Buck Moth.

Pupa:

The pupa is a dark rusty-brown and about 27-31 mm long (Davis pers. comm. 2015) (Figure 3), with females slightly larger than males (Ife pers. comm. 2015).

Figure 3. Ova (a) and male pupa (b) of Nuttall's Sheep Moth.
Photo of Ova (a) and male pupa (b) of Nuttall's Sheep MothX
(Photo Nicky Davis, with permission)
Long description for Figure 3

Two photos. Photo A shows a collection of Nuttall's Sheep Moth eggs, which are oval and whitish-grey. Photo B shows the pupa, which is a dark rusty-brown.

Population Spatial Structure and Variability

Elsewhere in its global range, Nuttall’s Sheep Moth has a colour form with less contrast (“uniformis”) associated with high elevations, which appears to have a stable genetic basis rather than being environmentally induced (Tuskes et al. 1996). No data are available for Canadian populations, which occur at lower elevations and are of the typical coloration. Mitochondrial DNA studies (e.g., Rubinoff and Sperling 2004) have been conducted for other Hemileuca species but not for Nuttall’s Sheep Moth.

Designatable Units

Nuttall’s Sheep Mothis being assessed as one designatable unit. There is no information on discreteness or evolutionary significance among populations, but in Canada the species occurs within a small contiguous area in the COSEWIC Southern Mountain Ecological Area.

Special Significance

Nuttall’s Sheep Moth is emblematic of a southern biogeographic element that reaches its northern limit in extreme southern B.C. The Antelope-Brush (Purshia tridentata) ecosystem of the arid south Okanagan Valley is one of the four most endangered ecosystems in Canada (Schluter et al. 1995) and the area supports approximately 15,000 invertebrate species, including provincially, nationally, and globally rare taxa such as the Behr’s Hairstreak (Satyrium behrii) which also depends upon Antelope-brush as a larval host plant (COSEWIC 2012; Cannings and Cannings 1995).

Hemileuca moths are a diverse genus and have long been favoured for study by amateur and professional entomologists, in part due to their diurnal habits and striking coloration. Regardless of this widespread interest, the genus remains poorly understood. Numerous researchers work on this genus as it remains a useful model for the study of biogeography, gene flow, and evolution (McElfresh and Millar 2001; Rubinoff and Sperling 2002, 2004).

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Distribution

Global Range

The global range of Nuttall's Sheep Moth extends from extreme southern British Columbia as far south as California, northern Arizona and New Mexico. Its core range is the dry interior of the Great Basin and Columbia River drainage, from the Cascade Mountains and Sierra Nevada east to the edge of the Rocky Mountains in western Montana, Wyoming, and Colorado (Figure 4).

Figure 4. Approximate global range of Nuttall's Sheep Moth. Adapted from Peigler and Opler (1993) and Tuskes et al. (1996) using records from Crabo et al. (2012) and Opler et al. (2014).
Map showing pproximate global range of Nuttall's Sheep Moth
Long description for Figure 4

Map of the global range of the Nuttall's Sheep Moth, which extends from extreme southern British Columbia as far south as California, northern Arizona and New Mexico. Its core range is the dry interior of the Great Basin and Columbia River drainage, from the Cascade Mountains and Sierra Nevada east to the edge of the Rocky Mountains in western Montana, Wyoming, and Colorado.

Canadian Range

In Canada, Nuttall’s Sheep Moth has only been observed from three general areas in the Okanagan Valley within 35 km north of the international border (Table 1, Figure 4). These are: 1) Osoyoos, 2) Oliver (precise site unknown), and 3) Vaseux Lake (two sites approximately 1400 m apart but with suitable intervening habitat). Nuttall’s Sheep Moth individuals were observed in 1986 at Haynes’ Lease Ecological Reserve approximately 8 km north of Osoyoos; it is not known if this is the same site as the 1920 and 1953 Osoyoos records. Vaseux Lake sites are at approximately 340 m elevation and Haynes’ Lease Ecological Reserve is at 350-370 m elevation. Canada has less than 1% of the global range and population and represents the northern limit of its continental range.

Table 1. Documented specimens and sightings of Nuttall's Sheep Moth in Canada.
Location
(as per label)
DateCollectorColl.Notes
Oliver1965-08-30H. KimmichUBC1F, wild-caught
Oliver1965-08-30unlabelledaUBC1M, wild-caught
Osoyoos1920-10-09E.H. BlackmoreUBC1M, reared from larvae
Osoyoos1920-10-10E.H. BlackmoreUBC1M, reared from larvae
Ozozoos, B.C.1953-08-25J.E.H. MartinCNC2 adults, wild-caught
Osoyoos, Haynes' Ecol. Res.1986-08-14B.A. MacdonaldUBC1M, wild-caught
Vaseux Lakeb1975-05-15C. Guppyfield obs.abundant half-grown to mature larvae
Vaseux Lakeb1976-05-15C. Guppyfield obs.abundant young to half-grown larvae
Vaseux Lakeb1987-08-25C. GuppyRBCM1 adult, reared from larvae
Vaseux Lakeb1987-09-04C. GuppyRBCM1 adult, reared from larvae
Vaseux Lakeb1987-09-05C. GuppyRBCM1 adult, reared from larvae
Vaseux Lakeb1988-04-27C. GuppyRBCM27 larvae collected from antelope brush
Vaseux Lakeb1988-05-11C. GuppyRBCM7 larvae collected from antelope brush
Vaseux Lakec1988S. Ife?RBCM1 larvae
Vaseux Lake1995-04-10M. Jacksonfield obs.1st instar larvae
Vaseux Lake1994-05-13M. Jacksonfield obs.3rd/4th instar larvae
Vaseux Lakec1997-05-15S. Ifefield obs.4th/5th instar larvae
Vaseux Lakec2002-05-20S. Ifefield obs.approximately fifty 4th and 5th instar larvae

a. Specimen can reasonably be assumed to be collected by Helmut Kimmich, who usually collected alone and donated his collection to the University of British Columbia Entomology collection (C. Guppy pers. comm. 2015).

b. UTM11, 316100E 5463600N, NAD83.

c. UTM11, 315272E 5464906N, NAD83.

The known Canadian range of Nuttall’s Sheep Moth is much more restricted than shown in Tuskes et al. (1996), which appears to be roughly based on the Canadian range of its larval host plant, Antelope-brush (Purshia tridentata). In B.C., Antelope-brush is restricted to two small areas: the lower elevations of the south Okanagan Valley and the Southern Rocky Mountain Trench of the East Kootenays. In the Okanagan, it is locally common and occurs in small, remnant patches of dry, sandy shrublands south of Penticton, although there are one or two small occurrences in the central Okanagan around Kelowna. In the Rocky Mountain Trench, Antelope-brush is restricted to scattered patches of grassland and Ponderosa Pine (Pinus ponderosa) woodland north to about Columbia Lake (Klinkenberg 2014; Parish et al. 1996; Schluter et al. 1995). Despite this wider range of Antelope-brush, Nuttall’s Sheep Moth apparently inhabits only the hottest portions of its host’s range in Canada.

Five specimens housed in the CNC and collected 1922 – 1956 from Waterton Lakes National Park were erroneously identified as uniformis variety of Nuttall’s Sheep Moth. These specimens were recently confirmed as Western Sheep Moth (Lonsdale pers. comm. 2014).

Extent of Occurrence and Area of Occupancy

The maximum extent of occurrence (minimum convex polygon) in Canada is 71 km2 based on the generalized UTMs of known records. The maximum index of area of occupancy (IAO) (2 km x 2 km grid) is 20 km2 (5 grid squares).

Search Effort

The Okanagan Valley is well-known “hotspot” for rare invertebrates in Canada (Cannings and Cannings 1995). This area has been the focus of numerous Lepidoptera surveys, particularly for Behr’s Hairstreak (Satyrium behrii), which inhabits the same Antelope-brush habitats (COSEWIC 2012) as Nuttall’s Sheepmoth. Unlike most moths, the large and colourful Nuttall’s Sheep Moth adults are diurnal, and detected without nocturnal surveys or specialized techniques (e.g., black lights). However, adults do not feed and can be difficult to identify on the wing or catch due to their rapid, erratic flight patterns (Tuskes et al. 1996). Hemileuca larvae are gregarious when young, and although large and distinctive as later instars, species determination can be problematic (St. John 2010). BothNuttall’s and Western sheep moths can be found at Vaseux Lake, although the former appears to reach final instar 2-3 weeks earlier than Western Sheep Moth (Ife pers. comm. 2014; St. John 2010).

To date, search effort in potential habitat is by wandering transect, searching for flying adults or larvae on Antelope-brush host plants. This is considered an efficient method for surveying diurnal Lepidoptera where distribution is poorly known and expected abundance is low (Haddad >et al. 2008; Hamm 2013). The use of reared, virgin Hemileuca females to attract males is an effective method to survey large areas and find new populations (Tuskes et al. 1996). To date, this technique has not yet been successful at confirming the presence of this Nuttall’s Sheep Moth in B.C. It is difficult to obtain female larvae and rear these to adults (Ife pers. comm. 2014).

There are fewer than 20 documented observations of Nuttall’s Sheepmoth since it was first recorded at Osoyoos in 1920 (Table 1).

Null search effort is summarized in Table 2. Recent search effort includes:

  • In 2009, six sites in Antelope-brush habitats in the southern Okanagan from August 24 to September 1, 2009. Approximately 24 person-hours and 26 km of wandering transect (Young and Marks 2009). Six adult Hera Buck Moths (Hemileuca hera) were recorded in about 40 min search effort in sagebrush-steppe at White Lake on August 26, 2009 (St. John pers. comm. as cited in Young and Marks 2009), suggesting that the timing of the survey was appropriate.
  • In 2014, over 6200 Antelope-brush plants at 18 sites in the Okanagan Valley were examined for Nuttall’s Sheep Moth larvae from May 26-29 during 30 person-hours and 30 km of wandering transects (Table 2). Survey timing was appropriate given the presence of approximately 35 Western Sheep Moth larvae (likely 4th instar based on size and date) found on Common Snowberry (Symphoricapos albus) and Wood’s Rose (Rosa woodsii) at one site near Vaseux Lake. No Nuttall’s Sheep Moth larvae were observed during these surveys.
Table 2. Summary of recent, unsuccessful, targeted surveys for larval (2014) and adult surveys (2009) for Nuttall's Sheep Moth in Canada.
Site NameApprox.
Easting
Approx.
Northing
Obs.dDate
Surveyed
Survey Time
(person-hours)
Survey
Length (km)
 # Purshia
Checked
Blue Mountain Property - TNT3154755466972VY, DM2009-08-283.03.6-
Fairview3108985449866VY, DM2009-08-243.34.2-
Haynes' Lease Ecol. Reserve3159895440420VY, DM2009-08-318.09.2-
Kennedy Property - TNT3164645459043VY, DM2009-08-243.24.0-
SOMA North3134075443846VY, DM2009-09-011.81.3-
SOMA South3146375441442VY, DM2009-09-014.74.0-
Fairview3107435449944RF, BR2014-05-281.72.5407
Haynes' Lease Ecol. Reserve3157285441013RF, BR2014-05-262.11.8105
Haynes' Lease Ecol. Reserve3159255440743RF, BR2014-05-292.34.0556
Hwy 3 East of Osoyoos3238125432411RF, BR2014-05-291.31.7180
Nk'mip Desert Cultural Centre3221625435300RF, BR2014-05-291.44.1161
Okanagan Falls - Allendale Road3149425466806RF, BR2014-05-2822.3563
Okanagan Falls - Antelope Brush CA3163555459127RF, BR2014-05-2723.0541
Okanagan Falls - Shuttleworth Cr. E3166425467215RF, BR2014-05-282.12.4462
Okanagan Falls - Shuttleworth Cr. W3159755467244RF, BR2014-05-284.44.3971
Oliver - near Covert Farms3140575457253RF, BR2014-05-272.12.1597
Osoyoos Desert Centre3161895436314RF, BR2014-05-271.41.7388
Osoyoos Bench3179365434011RF, BR2014-05-2921.7516
Testalinden3109495445203RF, BR2014-05-290.30.490
Vaseux Lake McIntyre Creek Road3174685462302RF, BR2014-05-270.80.599
Vaseux Lake North3154685464872RF, BR2014-05-261.91.8191
Vaseux Lake South - main3163835462990RF, BR2014-05-271.40.9116
Vaseux Lake South - ridge3164055463269RF, BR2014-05-270.60.645
White Lake Grasslands3128805456688RF, BR2014-05-2710.9240

d. Observers: VY=Vince Young; DM=Dawn Marks; RF=Rob Foster; BR=Brian Ratcliff

Table 3. Known and generalized Nuttall's Sheep Moth sites and threats.
Site NameVaseux Lake
(2 sites 1.6 km apart)
Osoyoos,
Haynes' Ecol. Res.
Oliver,
exact location unknown
Osoyoos/Ozozoos,
exact location
unknown
Threats Tally
(number of sites)
Yr First Recorded19751920?19651920?-
Yr Last Recorded2002198619651953-
Yr Last Surveyed20142014??-
Land OwnershipProtected / private conservation land (The Nature Trust)Protected (BC Parks; provincial Crown); and adjacent Wildlife Management Area (provincial Crown).??-
Search Effort NotesNumerous sites have been surveyed in 2009 and 2014; as well as by independent entomologistsNuttall's Sheepmoth only found on Haynes' Ecol. Res., although adjacent Wildlife Management Area also has Antelope-brush and moth likely uses this habitat.---
1.1 Housing & urban areasIntervening private lands could be developed.Adjacent private lands could be developed; housing development growing on property within 1km.Undesignated provincial crown land with Antelope-brush - pressure from Town of Oliver to purchase for urban expansion.The Town of Osoyoos would like to purchase part/all of a large parcel of provincial crown land with some Antelope-brush (approx 300ha) for town expansion.4
1.2 Commercial & industrial areasIntervening private lands could be developed.Adjacent private lands could be developedLess than residential, but ongoing. E.g., prison, industrial park expansion (however, few buildings).4
1.3 Tourism & recreation areasIntervening private lands could be developed.Adjacent private lands could be developedNot substantial.4
2.1 Annual & perennial non-timber cropsPrivate lands suitable for vineyard development.Adjacent private lands have been developed for vineyards; other adjacent properties with high potential for agricultural conversion.Private lands suitable for vineyard development.Private lands suitable for vineyard development.4
2.3 Livestock farming & ranchingAdjacent private lands currently have ranchingSome adjacent lands currently have ranching; Wildlife Management Area adjacent to Haynes' Lease is grazed and Nuttall's Sheepmoth likely uses this habitat too.Unknown; some Antelope-brush habitats are grazed.Unknown; some Antelope-brush habitats are grazed.At least 2
3.2 Mining and quarryingPrivate lands have previously had aggregate pitsPotential on adjacent landsUnknown.Unknown.At least 2
4.1 Roads and railroadsPotential on adjacent landsPotential on adjacent landsPotentialPotentialUnknown
4.2 Utility & service linesPotential on adjacent landsPotential on adjacent landsPotentialPotentialUnknown
6.1 Recreational activitiesminor potential from ATV use on private landsminor potential from ATV use on adjacent private landsminor potential from ATV use on private landsminor potential from ATV use on private landsNot significant, although in unchecked habitats.
7.1 Fire and Fire suppressionfire and fire suppression has occurred recentlyfire and fire suppression a riskfire and fire suppression a riskfire and fire suppression a risk-
8.1 Invasive non-nativespotential but impact unknown on species or host plantpotential but impact unknown on species or host plantpotential but impact unknown on species or host plantpotential but impact unknown on species or host plantunknown threat
8.2 Problematic native speciesnone knownnone knownnone knownnone knownlow threat
9.3 Agricultural & forestry effluentspotential agrochemical drift but impact, if any, unknownpotential agrochemical drift from adjacent vineyards; impact unknown. Overspray of irrigation systems has changed the vegetation adjacent to the site.potential agrochemical drift but impact, if any, unknownpotential agrochemical drift but impact, if any, unknown4
11.1 Habitat shifting & alterationpotential but impact unknown on species or host plantpotential but impact unknown on species or host plantpotential but impact unknown on species or host plantpotential but impact unknown on species or host plant4
11.2 Droughtspotential but impact unknown on species or host plantpotential but impact unknown on species or host plantpotential but impact unknown on species or host plantpotential but impact unknown on species or host plant4

There are some areas of the Okanagan that have not been searched for the moth. Approximately 8800 ha of mapped Antelope-brush habitat on the east side of the Okanagan Valley between Okanagan Falls and Osoyoos governed by local First Nations has not been searched (Figure 5). There are some potentially suitable habitats on private land within the species’ range, but many of the higher quality Antelope-brush habitats have had past surveys. No targeted surveys for Nuttall’s Sheep Moth have been documented for the Kootenay region, although they have been recommended (St. John 2010).

Figure 5. Distribution of Nuttall's Sheep Moth in Canada in relation to Antelope-brush (Purshia tridentata) habitat in the Okanagan Valley.
Map showing distribution of Nuttall's Sheep Moth in Canada
Long description for Figure 5

Map showing the distribution of the Nuttall's Sheep's Moth in Canada in relation to Antelope-brush habitat in the Okanagan Valley. Symbols indicate observations of the Nuttall's Sheep Moth at Osoyoos, Oliver (precise site unknown), Vaseux Lake (two sites) and Haynes' Lease Ecological Reserve, north of Osoyoos. The locations of surveys for adults and larvae in 2009 and 2014, respectively, are also shown.

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Habitat

Habitat Requirements

All known Canadian records for Nuttall’s Sheep Moth are within the Antelope-brush/Needle-and-Thread Grass (Purshia tridentata / Hesperostipa comata) community in the hotter, lower parts of the Antelope-brush distribution within the Okanagan (St. John 2010; Lea et al. 2004) (Figures 5 & 6). In Canada, Nuttall’s Sheep Moth has only been recorded feeding on Antelope-brush (St. John 2010), but elsewhere it has also been recorded on other shrubs, including snowberries (Symphoricarpos spp.) (see Life Cycle and Reproduction). Antelope-brush has a small occurrence within the east Kootenays.

In the United States, adults are always associated with sagebrush scrub and pinyon-juniper woodland habitats at lower elevations and with sagebrush meadows at higher elevations (Tuskes et al. 1996). However, at the northern edge of its global range in Canada, Nuttall’s Sheep Moth appears to be found only in the hotter areas of Antelope-brush dominated habitat.

Figure 6. Nuttall's Sheep Moth habitat with Antelope-brush at Haynes' Lease Ecological Reserve near Osoyoos, looking southeast.
Photo of Nuttall's Sheep Moth habitat
Photo by Rob Foster, May 26, 2014
Long description for Figure 6

Photo of Nuttall's Sheep Moth habitat with Antelope-brush at Haynes' Lease Ecological Reserve near Osoyoos, looking southeast.

Habitat Trends

The Antelope-brush/Needle-and-Thread Grass plant community has significantly declined in both quantity and quality since 1800 (Lea 2001, 2008; Schluter >et al. 1995). Spatial mapping of Antelope-brush habitats shows a reduction of 9800 ha in 1800 to about 3200 ha in 2008; or approximately 1/3 of its original extent (Iverson 2012). Within B.C, none of the remaining Antelope-brush/Needle-and-Thread Grass community is considered to have excellent ecological integrity, with 54% assessed as having good ecological integrity and 46% having fair or poor ecological integrity (Iverson 2012). Antelope-brush has only been mapped for the southern Okanagan Valley (Woods pers. comm. 2014), with limited potential habitat in the north Okanagan and the Kootenay areas.

Historically, Antelope-brush habitats experienced frequent, low intensity fires (Lea 1996; Lea et al. 2004), but recent high-intensity fires likely have a greater risk to local populations of Nuttall’s Sheep Moth (see Threats). During the mid-2000s, there were extensive fires within the Okanagan Valley, and Antelope-brush habitats were significantly impacted from these fires (Dyer pers. comm. 2015). A human-caused fire burned previously occupied habitat for Nuttall’s Sheep Moth in 2003 near Vaseux Lake on Nature Trust of B.C. property, destroying much of the Antelope-brush there (Figure 7).

Figure 7. Fire-killed Antelope-brush at previously documented Nuttall's Sheep Moth habitat east of Vaseux Lake, May 27, 2014 (looking north).
Photo of fire-killed Antelope-brush.
Photo by Rob Foster, May 26, 2014.
Long description for Figure 7

Photo of fire-killed Antelope-brush at previously documented Nuttall's Sheep Moth habitat east of Vaseux Lake, looking north.

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Biology

Life Cycle and Reproduction

Nuttall’s Sheep Moth typically have a one year life cycle, but may need two years to complete development at high elevations and northern latitudes (Opler et al. 2014). This life cycle has been reported for Western Sheep Moth (Evans 1958). Females lay 50-200 eggs in rings around host plant stems in late summer, which then overwinter. Larvae hatch in May to early June (Tuskes et al. 1996), but 1st instar caterpillars have been found near Vaseux Lake, B.C. as early as April 10 (Table 1). Larvae are gregarious when young but disperse as 3rd or 4th instars to feed alone. There are five instars and fully-grown caterpillars pupate in loose cocoons in leaf litter or burrows in soft soil (Tuskes et al. 1996; Davis 2014). Adults emerge later that season, or possibly the following year (St. John 2010).

In B.C., early instars have only been observed feeding on Antelope-brush (Guppy pers. comm. 2014), but elsewhere in their range larvae have also been reported on snowberry (Symphoricarpos spp.) (Opler et al. 2014), Desert Sweet (Chamaebatiaria millefolium), and currants (Ribes spp.) (Tuskes et al. 1996). Larvae have been reared on Common Snowberry (S. albus), Roundleaf Snowberry(S. rotundifolius), Douglas’ Meadowsweet (Spiraea douglasii), and Birchleaf Mountain Mahogany (Cercocarpus betuloides) (Davis 2014; S. Ife pers. comm. 2014; Tuskes 1984; McFarland, 1974). Currant and snowberry occur in Antelope-brush habitats within the range of Nuttall’s Sheep Moth in British Columbia, and could potentially serve as larval host plants.

Adults have been observed in the Okanagan Valley from August 14-30, which falls within the expected flight period based on approximately 40 records from elsewhere in the northern parts of its range in the United States (Figure 8). In the southern parts of its range in the United States the flight season is from July to early September, with a peak in early August, and earlier at high elevations (Tuskes et al. 1996). Two adults reared from larvae by Blackmore in 1920 did not emerge until October 9-10 (Table 1).

As with other Hemileuca, adult Nuttall’s Sheep Moths do not feed and have a short life span of several days (Tuskes et al. 1996). Both sexes are active daytime fliers and their brief flight period is devoted to reproduction (Collins and Tuskes 1979). Adults emerge in the morning but mating does not occur until early afternoon. Collins and Tuskes (1979) showed that in California, peak flight of adults occurs from 13:30 to 16:30, just after the peak flight of sympatric Western Sheep Moths. Females emit pheromones that flying males use to locate potential mates, and diurnal activity patterns contribute to reproductive isolation among species.

Figure 8. Seasonality of adult flight season for Nuttall's Sheep Moth in the Pacific Northwest (Crabo et al. 2012).
Bar chart illustrating the adult flight season for the Nuttall's Sheep Moth in the Pacific Northwest
Long description for Figure 8

Bar chart illustrating the adult flight season for the Nuttall's Sheep Moth in the Pacific Northwest. Adults have been observed in the Okanagan Valley from August 14 to 30. In the southern parts of its range in the United States the flight season is from July to early September.

Physiology and Adaptability

Nuttall’s Sheep Moth has some physiological and ecological adaptability, with known larval host plants from several different plant families. Of these, Antelope-brush is known to produce a variety of secondary compounds including the cyanoglucosides purshianin and menisdaurin (Nakanishiet al. 1994), but it is not known how this may affect the physiology and ecology of Nuttall’s Sheep Moth.

Throughout its range, Nuttall’s Sheep Moth occurs from low elevation to over 2500 m altitude and has a north-south range of approximately 1500 km. Daily sunlight is necessary for larvae to feed and grow, and adults tend to fly mainly in sunny weather (MacFarland 1974; Powell and Opler 2009).

Dispersal and Migration

No studies have reported dispersal distances for Nuttall’s Sheep Moth. However the related Nevada Buck Moth (H. nevadensis)readily flies for short distances over highly unsuitable environments. Dispersal of up to at least 4 km has been documented for New England Buck Moth (H. lucina) (NatureServe 2014).

Interspecific Interactions

Many vertebrate predators that typically consume caterpillars may avoid Nuttall’s Sheep Moth due to the venomous spines. However, adults may fall prey to insectivorous birds and spiders (Aranaeidae). Ants (Formicidae) and beetles (Coleoptera) have been observed preying upon the larvae or pupae of other Hemileuca species (COSEWIC 2009; Pryor 1998). The parasitoids Enicospilus americanus (Hymenoptera: Ichneumonidae) and Cotesia sp. (Hymenoptera: Braconidae) are known to attack Nuttall’s Sheep Moth larvae (Collins 1974). At times more than 90% of mature Hemileuca larvae can be parasitized, although 1st and 2nd instar larvae are usually free of parasitoids (Tuskes et al. 1996).

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Population Sizes and Trends

Sampling Effort and Methods

Surveys for Nuttall’s Sheep Moth have focused on recording the species presence within a habitat. See Survey Effort.

Abundance

Populations at historical sites, if any, are likely small. Surveys in 2009 and 2014, and lack of other recent records support this inference. In 1975-76, Nuttall’s Sheep Moth larvae “likely totalled in the many thousands” at the site east of Vaseux Lake with “larvae in sight at almost all times along a 500 m survey transect (C. Guppy pers. comm. 2014). Approximately 50 larvae were last observed at the Vaseux Lake “north” site May 20, 2002, and were abundant in previous years (Ife pers. comm. 2014). However, after a wildfire at the Vaseux Lake site in 2004, no caterpillars or sign of feeding were observed on May 15, 2011 (Ife pers. comm. 2014), nor in 2014 (Foster pers. comm. 2014; Ratcliff pers. comm. 2014).

Fluctuations and Trends

There is no information on Canadian or global population trends. No Nuttall’s Sheep Moths were observed at Haynes’ Lease Ecological Reserve or Vaseux Lake sites in 2014. However, due to low detectability and short adult life span, these populations are presumed extant. It is unknown if the older specimens for “Osoyoos” (1920) and “Ozozoos” (1953) are from what is now Haynes’ Lease Ecological Reserve, or from somewhere else in the Osoyoos area. The precise location and fate of the 1965 “Oliver” population are unknown but it is possibly extirpated (or may be the same site as Vaseux Lake).

Nuttall’s Sheep Moth likely experiences extreme fluctuations in abundance. The abundant larval observations in 1975-76, and again in 2002 (see Abundance), suggest the possibility of extreme fluctuations in adult moths. In order to produce large numbers of larvae, large numbers of eggs would have overwintered on the host plant stems. Larvae hatch in the spring and begin feeding and presumably, many of these larvae would fall to the soil to pupate. Some of these pupae may remain dormant for more than one season. A threatening event, such as a wildfire, could decimate a population of the moths at the egg stage or larval stage (e.g., brush fire that kills Antelope-brush), or during the pupal stage (e.g., ground or surface fire) if it were to occur during one of these large population events. Other sheep moth populations are known to experience extreme fluctuations in abundance (Schmidt pers. comm. 2015).

Rescue Effect

Given their strong flying ability, Nuttall’s Sheep Moths could potentially immigrate from northern Washington State or Idaho. They have been confirmed from Brewster, WA (Crabo et al. 2012) approximately 100 km south of Osoyoos, and there appears to be suitable intervening habitat (LaBar pers. comm. 2015; Swedberg pers. comm. 2015) and potentially undetected populations along the intervening Okanagan Valley.

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Threats and Limiting Factors

The International Union for Conservation of Nature-Conservation Measures Partnership (2006) (IUCN-CMP) threats calculator was used to classify and list threats to the Nuttall’s Sheep Moth(Salafsky et al. 2008; Master et al. 2009). The results of the threats calculator were High – Medium. These threats are listed from highest to lowest.

The cumulative loss, degradation, and fragmentation of the Antelope-brush ecosystem are the primary threats to Nuttall’s Sheep Moth (Figure 9). The ecological integrity and condition of Antelope-brush grasslands have been severely reduced: fragmentation by agricultural (particularly vineyard) and urban/suburban development, alteration to fire regimes, overgrazing from domestic livestock, and the spread and continued introduction of invasive alien plants (Iverson 2012). These factors continue to threaten the remaining occurrences of this ecological community (Iverson 2012).

The classification below is based on the IUCN-CMP (World Conservation Union–Conservation Measures Partnership) unified threats classification system. For a detailed description of the threat classification system, see the CMP website (CMP 2010). Threats may be observed, inferred, or projected to occur in the near term. Threats are characterized here in terms of scope, severity, and timing. Threat “impact” is calculated from scope and severity. For information on how the values are assigned, see Master et al. (2009) and table footnotes for details.

Species or Ecosystem Scientific Name:
Nuttall's Sheep Moth (Hemileuca nuttalli)
Date:
January 5, 2015
Assessor(s):
Rob Foster (Northern Bioscience; report co-writer), Orville Dyer (BC Ministry of Forests, Lands and Natural Resource Operations, Penticton); Jenny Heron (COSEWIC Arthropods Co-chair); Dave Fraser (BC); Christian Schmidt (Arthropods SSC).
Overall Threat Impact Calculation Help:
Threat ImpactThreat Impact (descriptions)Level 1 Threat Impact Counts:
high range
Level 1 Threat Impact Counts:
low range
AVery High00
BHigh20
CMedium02
DLow11
-Calculated Overall Threat Impact:Very HighMedium
Table 4. IUCN Threats Calculator results for Nuttall's Sheep Moth (Hemileuca nuttalli) in Canada.
#ThreatImpact
(calculated)
Scope
(next
10 Yrs)
Severity
(10 Yrs
or
3 Gen.)
TimingComments
1Residential and commercial developmentBC High-MediumLarge - Restricted (11-70%)Extreme (71-100%)HighA primary threat due to human growth and increasing land development in Okanagan, particularly valley bottom antelope-brush ecosystems
1.1Housing and urban areasBC High-MediumLarge - Restricted (11-70%)Extreme (71-100%)HighPossible at 3 sites, particularly in Osoyoos and Oliver areas, but many sites in protected areas or land trusts
1.2Commercial and industrial areasC-MediumRestricted (11-30%)Extreme (71-100%)HighPenticton and Osoyoos areas primarily, and potentially at undocumented sites
1.3Tourism and recreation areasD-LowSmall (1-10%)Extreme (71-100%)HighMainly for golf courses and resort development, such as has already occurred on First Nation land
2Agriculture and aquacultureBC High-MediumLarge - Restricted (11-70%)Extreme (71-100%)HighVineyard development and expansion are a major threat to Antelope-brush habitats on which Nuttall's Sheep Moth are dependent.
2.1Annual and perennial non-timber cropsBC-Medium-HighLarge - Restricted (11-70%)Extreme (71-100%)HighVineyard development and expansion are a major threat to Antelope-brush habitats on which Nuttall's Sheep Moth are dependent.
2.3Livestock farming and ranchingNegligiblePervasive (71-100%)Negligible (<1%)HighWidespread livestock grazing but negligible impacts on host plant or unpalatable larvae except perhaps at very high livestock densities or drought
3Energy production and miningNegligibleNegligible (<1%)Serious (31-70%)High-
3.2Mining and quarryingNegligibleNegligible (<1%)Serious (31-70%)HighGravel extraction a localized threat for habitat loss
4Transportation and service corridorsNegligibleNegligible (<1%)Extreme (71-100%)High-
4.1Roads and railroadsNegligibleNegligible (<1%)Extreme (71-100%)ModerateRoad expansion in Okanagan has some limited potential for destruction and fragmentation of habitat
4.2Utility and service linesNegligibleNegligible (<1%)Slight (1-10%)ModerateLimited disturbance during construction of power lines but antelope brush can persist in rights-of-way
5Biological resource use-----
5.1Hunting and collecting terrestrial animalsNA---Not applicable - not easily found and difficult to catch
6Human intrusions and disturbanceNegligibleNegligible (<1%)Serious (31-70%)HighRecreationalists unlikely to disturb stinging caterpillars and adults are swift flyers
6.1Recreational activitiesNegligibleNegligible (<1%)Serious (31-70%)HighAll-terrain vehicle use may have a local effect on habitat but is not permitted at known extant sites
7Natural system modificationsD-LowSmall (1-10%)Extreme (71-100%)Moderate-
7.1Fire and fire suppressionD-LowSmall (1-10%)Extreme (71-100%)ModerateWildfires can result in the loss of antelope-brush habitats, although are typically fairly localized due to fire suppression. Effects of antelope-brush ecosystems due to fire suppression less clear and unlikely to be felt in next 10 years.
8Invasive and other problematic species and genesNegligiblePervasive (71-100%)Negligible (<1%)HighThe impacts from invasive plants are not likely to impact pupation sites or sandy substrates available to the moth, at the base of the plant. Nectar sources are not an issue because they don't feed as adults.
8.1Invasive non-native/alien speciesNegligiblePervasive (71-100%)Negligible (<1%)HighNo known invasive plant that is currently threatening antelope brush. Potential impacts from introduced tachinid fly (Compsilura concinnata)
9PollutionUnknownSmall (1-10%)UnknownHigh-
9.3Agricultural and forestry effluentsUnknownSmall (1-10%)UnknownHighDrift of herbicides and pesticides from agricultural fields (e.g., vineyards) adjacent to occupied habitat is a threat to host plant and Nuttall's Sheep Moth
10Geological events-----
10.3Avalanches/landslidesNA---There have been a few landslides in the past ten years but this has not impacted substantial Antelope-brush habitat and this is considered negligible within the next ten years.
11Climate change and severe weatherUnknownPervasive (71-100%)UnknownHighClimate suitability for antelope-brush grasslands in Canada could potentially increase as a result of climate change, but an increase in severe weather events could negatively impact populations of Nuttall's Sheep Moth
11.1Habitat shifting and alterationUnknownPervasive (71-100%)UnknownHighSome ecological changes may benefit this species
11.2DroughtsUnknownPervasive (71-100%)UnknownHighAn increase in the frequency and intensity of summer drought could result in premature senescence of larval host plants, or may change rain patterns during the larval period, potentially reducing juvenile survival.
11.4Storms and floodingUnknownPervasive (71-100%)UnknownHighSmall, isolated populations of Nuttall's Sheep Moth are likely vulnerable to stochastic events and could be threatened by hailstorms or severe frost, particularly if the frequency and intensity of severe weather events increases due to climate change.

Glossary

Impact
The degree to which a species is observed, inferred, or suspected to be directly or indirectly threatened in the area of interest. The impact of each threat is based on Severity and Scope rating and considers only present and future threats. Threat impact reflects a reduction of a species population or decline/degradation of the area of an ecosystem. The median rate of population reduction or area decline for each combination of scope and severity corresponds to the following classes of threat impact: Very High (75% declines), High (40%), Medium (15%), and Low (3%). Unknown: used when impact cannot be determined (e.g., if values for either scope or severity are unknown); Not Calculated: impact not calculated as threat is outside the assessment timeframe (e.g., timing is insignificant/negligible or low as threat is only considered to be in the past); Negligible: when scope or severity is negligible; Not a Threat: when severity is scored as neutral or potential benefit.
Scope
Proportion of the species that can reasonably be expected to be affected by the threat within 10 years. Usually measured as a proportion of the species' population in the area of interest. (Pervasive = 71–100%; Large = 31–70%; Restricted = 11–30%; Small = 1–10%; Negligible < 1%).
Severity
Within the scope, the level of damage to the species from the threat that can reasonably be expected to be affected by the threat within a 10-year or three-generation timeframe. Usually measured as the degree of reduction of the species' population. (Extreme = 71–100%; Serious = 31–70%; Moderate = 11–30%; Slight = 1–10%; Negligible < 1%; Neutral or Potential Benefit > 0%).
Timing
High = continuing; Moderate = only in the future (could happen in the short term [< 10 years or 3 generations]) or now suspended (could come back in the short term); Low = only in the future (could happen in the long term) or now suspended (could come back in the long term); Insignificant/Negligible = only in the past and unlikely to return, or no direct effect but limiting.
Comments
see main body of text (Threats and Limiting Factors) for details

Agriculture and Aquaculture (high – medium impact) (2)

Annual and perennial non-timber crops (2.1)

Vineyard development and expansion are a major threat to Antelope-brush habitats (Iverson 2012). The Antelope-Brush / Needle-and-Thread Grass plant community is rapidly being converted to vineyards because the ecological community is considered an indicator for high grape crop production and is targeted by the wine industry for development (Dyer pers. comm. 2014; COSEWIC 2012). Much of the remaining Antelope-brush habitat near Vaseux Lake, Osoyoos and Oliver is suitable for vineyards, orchards, or other agricultural development. Historically, the conversion of habitat to vineyards and other agricultural use (see Habitat Trends) has likely been a contributing factor to the fragmentation of Nuttall’s Sheep Moth populations.

Livestock farming and ranching (2.3)

Livestock grazing occurs at a number of sites, although the intensity or frequency is unknown. When alternate forage is limited (e.g., during drought), cattle grazing on Antelope-brush could result in increased mortality or reduced fitness of Nuttall’s Sheep Moths. Browsing of Antelope-brush may reduce food availability for larvae, and livestock could inadvertently ingest eggs or trample pupae.

Residential or Commercial Development (very high – medium impact) (1)

Housing and urban areas (1.1); Commercial and industrial areas (1.2) and Tourism and recreation areas (1.3) are all considered primary threats to the Canadian populations of Nuttall’s Sheep Moth due to human population growth and increasing land development in the Okanagan. Antelope-brush ecosystems are within the valley bottom of the Okanagan valley, areas with the highest probability of development. The population of the Okanagan itself has tripled every 30 to 40 years since 1940 (Jensen and Epp 2002) and is projected to experience significant growth over the next two decades (Hobson and Associates 2006). Coincident with this growth is the loss, degradation, and fragmentation of Antelope-brush habitats and other natural ecosystems in the region. Large multi-housing developments are being constructed (as of 2015) close to Haynes’ Lease Ecological Reserve and in many of the remaining Antelope-brush habitats surrounding the Town of Osoyoos.

Natural System Modifications (low impact) (7)

Fire and fire suppression (7.1)

Frequent, low-intensity wildfires were likely once more common throughout Antelope-brush habitats (Daigle 1996; Young and Clements 2002). Fires were likely ignited by First Nations peoples to improve root crops, and by lightning (Iverson 2012; Cannings and Durance 1998). Fire suppression activities have altered the natural fire regime in the Okanagan Valley, however, and appear to have increased fire intensity and severity (Iverson 2012). Larger stand-replacing fires may result, rather than smaller, less intense surface and patchy fires that otherwise leave Antelope-brush plant community patches intact.

Antelope-brush is very susceptible to fire-kill, with few plants re-sprouting following fire (Zlatnik 1999). After fire, Antelope-brush plants may persist in rocky refugia or in the skips of a patchy burn (Krannitz and Mottishaw 2003); these remaining individuals and any other survivors may also provide a seed source to re-establish Antelope-brush in adjacent areas (Young and Clements 2002; Shatford 1997).

A large (3000+ ha) fire burned much of the Antelope-brush habitat southeast of Vaseux Lake in early September 2003 (BC Ministry of Environment unpublished data) (Figure 7), including one of the two known sites for Nuttall’s Sheep Moth (Vaseux Lake South). Although they were abundant there in 2002, Nuttall’s Sheep Moths have not been observed at Vaseux Lake since the fire. A large fire also burned all but the southernmost 1/5 of Haynes’ Lease Ecological Reserve in 1993, killing approximately 95% of the Antelope-brush (Roemer 1993). Antelope-brush is now relatively abundant at the site, but Nuttall’s Sheep Moth has not been observed there since the fire. High-intensity fires, even of small size, could potentially have significant impacts on localized populations of Nuttall’s Sheep Moth due to highly fragmented landscapes in the south Okanagan. Invasive non-native plants such as Cheatgrass increase the amount of fine fuels in Antelope-brush plant communities.

Tree encroachment, in the absence of frequent fire, may have also reduced the size and extent of Antelope-brush plants at some sites, due to shading and competition.

Energy Production and Mining (negligible impact) (3)

Mining and quarrying (3.2)

Gravel extraction is a localized threat to the Nuttall’s Sheep Moth habitat. Several small gravel pits are located at or near the known Vaseux Lake sites, although it is not known if they are active.

Transportation and Service Corridors (negligible impact) (4)

Construction of new roads (4.1) and utility and service lines (4.2) have the potential to destroy or fragment Antelope-brush habitat upon which Nuttall’s Sheep Moth depends.

Human Intrusions and Disturbance (negligible impact) (6)

Human intrusion and disturbance are likely only a minor threat. Caterpillars have stinging spines and adults are very swift flyers so are unlikely to be directly disturbed by recreationalists or other backcountry users. All-terrain vehicle use may have a local effect on habitat but is not permitted at known extant sites.

Invasive and Other Problematic Species and Genes (negligible impact) (8)

Invasive non-native/alien species (8.1)

Many non-native plant species are found throughout Antelope-brush ecosystems, and some appear to have little impact on the ecosystem (Symonds 2011). However, invasive non-native species such Cheatgrass (Bromus tectorum), Sulphur Cinquefoil (Potentilla recta), Diffuse Knapweed (Centaurea diffusa), and Dalmatian Toadflax (Linaria genistifolia ssp. dalmatica) can have significant adverse impacts on the Antelope-brush habitats (Iverson 2012) upon which Nuttall’s Sheep Moth is dependent. For example, Sulphur Cinquefoil can form monospecific stands and may prevent re-establishment of Antelope-brush plants after wildfires (SIRT 2008).

Parasitoid tachinid flies such as Compsilura concinnata (Tachinidae) introduced into eastern North America as biological control agents for European Gypsy Moth (Lymantria dispar) have also impacted native Lepidoptera populations including Hemileuca (Boettner et al. 2000). C. concinnata is the most likely cause of the reported decline of giant silk moths in the northeastern United States (Elkinton and Boettner 2012), and although it has been reported from British Columbia (Sabrosky and Reardon 1976), possible effects on Nuttall’s Sheep Moth are unknown. Compsilura concinnata wasassessed as a possible bio-control agent for Cabbage Looper (Trichoplusia ni, Lepidoptera: Noctuidae) infesting commercial greenhouses in B.C., but its use was considered ineffective for greenhouse settings (Caron 2005).

Pollution (unknown impact) (9)

Agricultural and forestry effluents (9.3)

Presumed extant locations at Vaseux (Figure 9) and Haynes’ Lease are immediately adjacent to vineyards so pesticide drift is a potential threat to larvae and adults. Agricultural fields are common in the Osoyoos and Oliver areas, as well as elsewhere in the Okanagan Valley. Drift of herbicides could potentially affect the larval host plant as well, although it is unknown how susceptible Antelope-brush is to commonly used agrochemicals.

Figure 9. GoogleEarth image (8/3/2012) of Nuttall's Sheep Moth record (S. Ife) east of Vaseux Lake showing vineyards, aggregate extraction, and residential development surrounding remaining Antelop-brush habitat.
GoogleEarth image (8/3/2012) of Nuttall's Sheep Moth
Long description for Figure 9

GoogleEarth image showing the location of a Nuttall's Sheep Moth record east of Vaseux Lake and the vineyards, aggregate extraction, and residential development surrounding the remaining Antelop-brush habitat.

Climate Change and Severe Weather (unknown impact) (11)

Droughts (11.2)

Climate change, particularly an increase in the frequency and intensity of extreme and periodic climatic events such as droughts, could be a long-term threat to Canadian populations of Nuttall’s Sheep Moth. Decreased precipitation and increased mean annual temperatures associated with climate change might reduce host plant fitness and abundance in the short-term, but might also lead to an eventual northward range extension of Antelope-brush.

Climate change is a potential but poorly understood threat to Nuttall’s Sheep Moth in the south Okanagan, primarily due to potential impacts on Antelope-brush habitats. In particular, an increase in the frequency and intensity of summer drought could result in premature senescence of larval host plants, or may change rain patterns during the larval period, potentially reducing juvenile survival. Although climate suitability for Antelope-brush grasslands in Canada could potentially increase as a result of climate change (Wilson and Hebda 2008), range expansion is unlikely given the current rates of habitat loss and low rates of dispersal for both Antelope-brush and Nuttall’s Sheep Moth.

Storms and flooding (11.4)

Small, isolated populations of Nuttall’s Sheep Moth are likely vulnerable to stochastic events and could be threatened by hailstorms or severe frost, particularly if the frequency and intensity of severe weather events increases due to climate change.

Limiting Factors

Canadian populations of Nuttall’s Sheep Moth are vulnerable due to their small population size, short adult life span, non-feeding adult life stage, host plant specificity, and specific Antelope-brush plant community habitat requirements.

Number of Locations

Three locations are proposed for Nuttall’s Sheep Moth in Canada based on a combination of threats and land tenure: (i) The Vaseux Lake area has areas that are protected (e.g., The Nature Trust of B.C., Vaseux Bighorn National Wildlife Area) but there could be potential effects from wildfire and the overgrazing of livestock on other Crown and private properties; (ii) The Oliver area is perceived to be at greater risk of residential and agricultural (e.g., vineyard) development; and (iii) the Osoyoos area has some substantial Antelope-brush communities on First Nation lands and the smaller Haynes’ Lease Ecological Reserve, but other areas have been heavily developed. Haynes’ Lease Ecological Reserve is threatened by wildfire.

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Protection, Status and Ranks

Legal Protection and Status

The Nuttall’s Sheep Moth is not protected under the federal Species at Risk Act or British Columbia’s Wildlife Act. It is not listed under the US Endangered Species Act or the Convention on International Trade in Endangered Species of Wild Fauna and Flora.

Non-Legal Status and Ranks

Global status rank:
G5 (Secure; NatureServe 2014).
Canada national status rank:
Not ranked.
British Columbia status rank:
Not ranked. United States, state ranks: Colorado S4 (Apparently Secure); Not ranked in the other nine states where it occurs.
General status rank:
May be at Risk in the WildSpecies (2010) report (CESCC 2011).

Habitat Protection and Ownership

The most recent Nuttall’s Sheep Moth observations have been from protected areas. The 1975-76 and 2002 records from the Vaseux Lake area are on The Nature Trust of B.C. properties and the 1986 Osoyoos record was from Haynes’ Lease Ecological Reserve (BC Parks). The precise localities of other historical collections from Osoyoos and Oliver are unknown, but given current land tenure, there is a high probability they are on either private or First Nation land.

About 17% of the remaining Antelope-Brush / Needle-and-Thread Grass vegetation community is protected by the Canadian Wildlife Service National Wildlife Areas (3%), provincial Protected Areas (6%), and private conservation lands (8%) (Iverson 2012). The remaining 83% occurs in unprotected lands on Indian Reserves (56%), private land (20%), and provincial crown land (6%).

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Acknowledgements and Authorities Contacted

Brian Ratcliff ably assisted with 2014 fieldwork in the Okanagan Valley. Special thanks to Jennifer Heron (BC Ministry of Environment) and Orville Dyer (BC Ministry of Forests, Lands and Natural Resource Operations), who were once again invaluable for contacts, spatial data, reports, and Okanagan experience. Thank you to Sara Bunge and Mark Weston (BC Parks) for access to parks and protected areas in the region. Cris Guppy, Dennis St. John and Steve Ife generously shared their past observations of and insights about the species. Nicholas Burdock (The Nature Trust of B.C.), Denise Eastlick (Osoyoos Desert Society) and other land managers graciously granted permission to access their properties. Nicky Davis, Steve Ife, and Merrill A. Peterson generously provided photographs of the species. Angele Cyr (COSEWIC Secretariat) is thanked for her assistance in contract management, as is the Arthropods Species Specialist Subcommittee for document review and threats assessment (Chris Schmidt, Syd Cannings, Rob Cannings, Cory Sheffield and Paul Grant). Front cover photograph by Merrill A. Peterson.

Authorities Contacted

Acord, Brian. Lead Zoologist, California Natural Diversity Database (CNDDB), California Dept of Fish & Game, Sacramento, CA.

Anweiler, Gary.C. Associate, Strickland Museum, University of Alberta, Edmonton, AB.

Bunge, Sara. BC Parks and Protected Areas, Penticton, BC

Chaney, Allison. Biologist, Nevada Natural Heritage Program, Department of Conservation & Natural Resources, Carson City, NV.

Davis, Nicky. Member, Utah Lepidopterists’ Society, Salt Lake City, Utah.

Desjardins, Sylvie. Professor, UBC Okanagan, Kelowna, BC.

Dyer, Orville. Ecosystems Biologist, Ministry of Forests, Lands and Natural Resource Operations, Penticton, BC.

Fleckenstein, John. Zoologist, Washington Natural Heritage Program, Department of Natural Resources, Olympia, WA.

Gaines, Eleanor. Zoology Project Manager, Oregon Natural Heritage Information Center/Information Office of the Oregon Natural Resources Institute, Portland.

Guppy, Crispin. Senior Biologist, Ecofor Consulting Ltd., Whitehorse, YT.

Heron, Jennifer. Invertebrate Conservation Specialist. BC Ministry of Environment, Vancouver, BC.

Ife, Steve. Amateur entomologist, Vancouver BC.

Jones, Neil. Scientific Project Officer & ATK Coordinator, COSEWIC Secretariat, Environment Canada, Gatineau QC.

Kohler, Steve. Forest Entomologist, Montana Department of Natural Resources, (retired), Missoula, MT.

Kondla, Norbert G. Lepidopterist, Calgary, AB.

LaBar, Caitlin. Amateur Entomologist, Kelso, WA.

Lafontaine, Don, Entomologist, Canadian National Collection of Insects, Arachnids and Nematodes, Agriculture and Agri-Food Canada, Ottawa, ON.

Maxell, Bryce A. Senior Zoologist, Montana Natural Heritage Program, Helena, MT.

McIntyre, Patrick. Lead Scientist, California Natural Diversity Database, California Department of Fish and Wildlife, Sacramento, CA.

Oliver, George. Research Zoologist, Utah Natural Heritage Program, Utah Division of Wildlife Resources, Salt Lake City, UT.

Pelham, Jonathan P. Curator of Butterflies, Washington State Burke Memorial Museum, University of Washington, Seattle, WA.

Ross, Dana. Consulting Entomologist, Portland, OR.

Sovell, John. Invertebrate Zoologist and Ecologist, Colorado Natural Heritage Program, Colorado State University, Fort Collins, CO.

St. John, Dennis. Consulting Entomologist, Okanagan Falls, BC.

Stout, Todd. Member, Utah Lepidopterists’ Society, Salt Lake City, UT.

Sutter, Ben. Database Zoologist, Utah Natural Heritage Program, Salt Lake City, UT.

Tronstad, Lusha. Invertebrate Zoologist, Wyoming Natural Diversity Database, University of Wyoming, Laramie, WY.

Weston, Mark. BC Parks and Protected Areas, Penticton, BC

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Biographical Summary of Report Writers

Robert Foster is co-founder and principal of Northern Bioscience, an ecological consulting firm offering professional consulting services supporting ecosystem management, planning, and research. Dr. Foster has a B.Sc. in Biology from Lakehead University and a D. Phil in Zoology from the University of Oxford. Rob has worked as an ecologist in Ontario for over 20 years, and has authored or coauthored COSEWIC status reports on the Bogbean Buckmoth, Mormon Metalmark, Weidemeyer’s Admiral, Powesheik Skipperling, Lake Huron Grasshopper, Riverine Clubtail, Laura’s Clubtail, Rapids Clubtail, Gibson’s Big Sand Tiger Beetle, Northern Barrens Tiger Beetle, Hop-tree Borer, Georgia Basin Bog Spider, Broad-banded Forestsnail, Nahanni Aster, Crooked-stem Aster, Bluehearts, and Drooping Trillium, as well as recovery plans for rare plants, lichens, and odonates. Rob has conducted numerous odonate and other insect surveys for protected areas planning and environmental assessments in Ontario, as well as Manitoba, Minnesota, Quebec, and British Columbia.

Allan Harris is a biologist with over 25 years’ experience in northern Ontario. He has a B.Sc. in Wildlife Biology from the University of Guelph and an M.Sc. in Biology from Lakehead University. After spending seven years as a biologist with the Ontario Ministry of Natural Resources, he co-founded Northern Bioscience, an ecological consulting company based in Thunder Bay, Ontario. Al has authored or coauthored dozens of scientific papers, technical reports, and popular articles, including COSEWIC status reports for Lake Huron Grasshopper, Riverine Clubtail, Laura’s Clubtail, Rapids Clubtail, Gibson’s Big Sand Tiger Beetle, Northern Barrens Tiger Beetle, Powesheik Skipperling, Mormon Metalmark, Weidemeyer’s Admiral, Bogbean Buckmoth, Hop-tree Borer, Georgia Basin Bog Spider, Broad-banded Forestsnail, Nahanni Aster, Crooked-stem Aster, Bluehearts, Drooping Trillium and Small-flowered Lipocarpha. Al also authored the Ontario provincial status report for woodland caribou, and has authored or coauthored national and provincial recovery strategies for vascular plants and birds.

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Collections Examined

The following collections were searched for Canadian specimens of Nuttall’s Sheep Moth:

Canadian National Collection of Insects, Arachnids and Nematodes, Ottawa, ON (Owen Lonsdale)

Chicago Field Museum, Chicago, IL. (on-line search)

E.H. Strickland Entomological Museum, University of Alberta, Edmonton, AB (on-line search)

J.B. Wallis Museum, University of Manitoba, Winnipeg, MB. (Barb Sharanowski)

Royal Alberta Museum, Edmonton, AB. (Matthias Buck)

Royal British Columbia Museum, Victoria, BC. (Claudia Copley)

Royal Saskatchewan Museum, Regina, SK. (Cory Sheffield)

Spencer Entomological Collection, Beaty Biodiversity Museum, University of British Columbia, Vancouver BC (Karen Needham)

Yale Peabody Museum of Natural History, New Haven, CT (on-line search)

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