Species Profile

Half-moon Hairstreak

Scientific Name: Satyrium semiluna
Taxonomy Group: Arthropods
Range: British Columbia, Alberta
Last COSEWIC Assessment: April 2006
Last COSEWIC Designation: Endangered
SARA Status: Schedule 1, Endangered

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Quick Links: | Taxonomy | Description | Habitat | Biology | Threats | Protection | Recovery Initiatives | Recovery Team | National Recovery Program | Documents

Image of Half-moon Hairstreak


The two Canadian populations may belong to separate subspecies, but at present these populations are not named at the subspecies level.



The Half-moon Hairstreak is a small, drab butterfly. The individuals of the two Canadian populations have several different physical characteristics. For instance, males of the British Columbia population have a wingspan of 30 mm or more and are conspicuously larger than their counterparts from Alberta, where males have a wingspan of 25 mm. Predominantly brown or blackish brown on the dorsal wing surfaces, with varying quantities of black spots, slightly edged with white scaling, the colour of Half-moon Hairstreak depends on sex, subspecies, amount of flight wear, and age of museum specimens. Unlike many other species of hairstreaks, the Half-moon Hairstreak has no “tail” on the hindwing. In both Alberta and British Columbia, females are larger and are paler and greyer on the ventral side than the males. The eggs are greenish white, but some are tan coloured, possibly as a consequence of age. The caterpillar has a light green ground colour with whitish lateral chevrons and a dark brown head. Adult Half-moon Hairstreaks can be confused with Boisduval’s blue, a related butterfly that flies in the same areas and overlaps in flight period. Male Boisduval’s blues are blue on the dorsal wing surface and the females also normally have at least some basal blue on the dorsal surfaces of the wings.


Distribution and Population

The range of the Half-moon Hairstreak extends from extreme southern interior British Columbia south to central California and east to eastern Wyoming and northern Texas. In Canada, the species, which is restricted to the southwestern part of the country, occurs as two disjunct populations. The British Columbia population is known from six locations in the southern Okanagan Valley, from the Canada-United States border north to White Lake. This population is contiguous with populations in Washington. On the east side of the Rocky Mountains, Alberta has one known population, in Waterton Lakes National Park of Canada. This population is disjunct from the nearest known populations in the United States. In 2003, the Alberta population of the Half-moon Hairstreak was thought to be anywhere from several thousand to fewer than 10 000 adults. In 2004, only 250 adults were observed in this population. The reasons for this dramatic population decline are unknown, but it may have been caused by an unusually late killing frost in the area in the spring of 2004. The size of the British Columbia population is unknown, but could include 5000 to 15 000 adults, although this is a very approximate estimate. Population trends are unknown. The likelihood of a rescue effect from the United States to the Alberta population is very low because there are no known locations nearby. However, there is a possibility of a rescue effect to the British Columbia population. There are Half-moon Hairstreak populations in Washington a short distance from the British Columbia population.



In British Columbia, populations of Half-moon Hairstreak have been found at elevations of 600 to 1100 m in sagebrush/bluebunch wheatgrass habitat where silky lupine is present. The butterflies were found in areas that had reduced relief in comparison to surrounding steeper areas. The single Alberta population is restricted to grassland habitat with abundant lupines at 1300 m elevation in Waterton Lakes National Park.



The food plants used by Half-moon Hairstreak caterpillars (larvae) have not been confirmed in Canada, but lupines are thought to be used because of the association of the butterfly with lupines at all known sites in Canada and the confirmed use of lupines as the host plant in the United States. This species has one annual brood. Eggs are laid on lupines or in the leaf litter at the base of the plants, and the species overwinters in this form. The larval stage therefore occurs in spring, and adults emerge in the late spring or early summer. Adults of the British Columbia population have been found from late May to early July, and adults have been found in Alberta mainly in the last two weeks of July. In both provinces, adults were active during much of the daylight period. The likely association of the caterpillars with ants may be a significant factor in the biology of this species. Many of the caterpillars in this family of butterflies secrete a nutritious liquid that is consumed by attendant ants. In return, the ants guard the caterpillars from attacks by predators and parasites. This mutual assistance relationship could be a decisive factor in the distribution of the species, and it may partially determine the butterfly’s habitat requirements, since ants have specific habitat requirements that may differ from the butterfly’s habitat requirements. Thus two interacting sets of requirements may determine the suitability of an area for the Half-moon Hairstreak.



Both of the Canadian populations of the Half-moon Hairstreak are threatened by habitat loss and degradation. In British Columbia, the species occurs in an area that is under severe development pressure. In fact, its populations are subject to a wide variety of human activities that could reduce or extirpate local populations. Intensive livestock grazing is one of the most serious threats, particularly on private land where there are no restrictions to prevent overgrazing. Conversion of sagebrush grasslands to agriculture and habitat loss to development are considered to be other serious threats to these populations. For example, the amount of habitat at one of the Richter Pass locations may be reduced in the future through the expansion of an aggregate pit. In addition, the human population is growing at a rapid rate in the area and this is expected to continue. In parallel with increases in the human population, residential housing and road construction continue to consume habitat on Anarchist Mountain and housing expansion is very much an ongoing threat in the south Okanagan area. Finally, native grassland habitat is also being converted to intensive agricultural uses, including vineyards, which are undergoing rapid expansion in the area. In Alberta, the population is located in a national park where human threats are limited. However, the population may be limited primarily by flooding and possibly by severe spring frosts. This population is also threatened by an invasion of spotted knapweed. Continuation of the spread of spotted knapweed will alter the habitat either directly through competition for resources or as a consequence of weed control measures. Invasive weeds also pose a threat in British Columbia.



Federal Protection

The Half-moon Hairstreak is protected under the federal Species at Risk Act (SARA). More information about SARA, including how it protects individual species, is available in the Species at Risk Act: A Guide.

The population of this species that occurs in Waterton Lakes National Park of Canada, in Alberta, is protected under the Canada National Parks Act. The British Colombia population is not protected by any provincial law in British Columbia.

Provincial and Territorial Protection

To know if this species is protected by provincial or territorial laws, consult the provinces' and territories' websites.


Recovery Initiatives

Status of Recovery Planning

Recovery Strategies :

Name Recovery Strategy for the Half-moon Hairstreak (Satyrium semiluna) in Canada
Status Final posting on SAR registry


Recovery Team

South Okanagan Invertebrates at Risk Recovery Team

  • Orville Dyer - Chair/Contact - Government of BC
    Phone: 250-490-8244  Send Email
  • Jennifer Heron - Chair/Contact - Government of BC
    Phone: 604-222-6759  Fax: 604-660-1849  Send Email



PLEASE NOTE: Not all COSEWIC reports are currently available on the SARA Public Registry. Most of the reports not yet available are status reports for species assessed by COSEWIC prior to May 2002. Other COSEWIC reports not yet available may include those species assessed as Extinct, Data Deficient or Not at Risk. In the meantime, they are available on request from the COSEWIC Secretariat.

11 record(s) found.

COSEWIC Status Reports

  • COSEWIC assessment and status report on the Half-moon Hairstreak Satyrium semiluna in Canada (2006)

    The Half-moon Hairstreak, named after its type locality at Half-Moon Ranch in Wyoming, is a small drab hairstreak butterfly in the family Lycaenidae. The adult butterflies are brown or blackish brown on the dorsal wing surfaces and grayish brown on the ventral wing surfaces with variable amounts of white and black maculation. There are two distinct populations in Canada, one in British Columbia and the other in Alberta, and these entities may represent different subspecies.

COSEWIC Assessments

Response Statements

  • Response Statements - Half-moon Hairstreak (2006)

    The butterfly occurs as disjunct populations in two small, restricted areas at the northern extreme of the species’ range.  The species’ population has likely declined in the past as a result of habitat loss.  Both populations continue to be threatened by habitat loss and degradation. In British Columbia the species occurs in an area under severe pressure for development. In both Alberta and British Columbia, invasive weeds also pose a serious threat.

Recovery Strategies

  • Recovery Strategy for the Half-moon Hairstreak (Satyrium semiluna) in Canada (2016)

    Under the Accord for the Protection of Species at Risk (1996), the federal, provincial, and territorial governments agreed to work together on legislation, programs, and policies to protect wildlife species at risk throughout Canada. In the spirit of cooperation of the Accord, the Government of British Columbia has given permission to the Government of Canada to adopt the “Recovery Strategy for the Half-moon Hairstreak (Satyrium semiluna) in British Columbia and Alberta” under Section 44 of the Species at Risk Act. Environment Canada has included an addition which completes the SARA requirements for this recovery strategy.

Action Plans

  • Multi-species Action Plan for Waterton Lakes National Park of Canada and Bar U Ranch National Historic Site of Canada (2017)

    The Multi-species Action Plan for Waterton Lakes National Park of Canada and the Bar U Ranch National Historic Site of Canada applies to lands and waters occurring within the boundaries of the two sites: Waterton Lakes National Park of Canada (WLNP) and the Bar U Ranch National Historic Site of Canada (BURNHS). The plan meets the requirements for action plans set out in the Species At Risk Act (SARA (s.47)) for species requiring an action plan and that regularly occur in these sites. Measures described in this plan will also provide benefits for other species of conservation concern that regularly occur at WLNP and at BURNHS.


  • Order Acknowledging Receipt of the Assessments Done Pursuant to Subsection 23(1) of the Act (2007) (2007)

    This Order acknowledges receipt by the Governor in Council of the assessments of the status of 40 species done pursuant to paragraph 15(1)(a) and in accordance with subsection 23(1) of the Species at Risk Act (SARA) by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). The purpose of SARA is to prevent wildlife species from being extirpated or becoming extinct, to provide for the recovery of wildlife species that are extirpated, endangered or threatened as a result of human activity and to manage species of special concern to prevent them from becoming endangered or threatened.
  • Order Amending Schedule 1 to the Species at Risk Act (2007)

    Her Excellency the Governor General in Council, on the recommendation of the Minister of the Environment, pursuant to section 27 of the Species at Risk Act, hereby makes the annexed Order Amending Schedules 1 to 3 to the Species at Risk Act.

COSEWIC Annual Reports

  • COSEWIC Annual Report - 2006 (2006)

    2006 Annual Report to the The Minister of the Environment and the Canadian Endangered Species Conservation Council (CESCC) from the Committee on the Status of Endangered Wildlife in Canada.

Consultation Documents

  • Consultation on Amending the List of Species under the Species at Risk Act Terrestrial Species: December 2006 (2006)

    The Government of Canada proclaimed the Species at Risk Act (SARA) on June 5, 2003 as part of its strategy for the protection of wildlife species at risk. Attached to the Act is Schedule 1, the list of the species that receive protection under SARA, hereinafter referred to as the 'SARA list'. Canadians are invited to comment on whether all or some of the species included in this document should be added to the SARA list. Please submit your comments by March 16, 2007 for species undergoing normal consultations and by March 14, 2008 for species undergoing extended consultations.

Critical Habitat Descriptions in the Canada Gazette

Recovery Document Posting Plans

  • Environment and Climate Change Canada's Three-Year Recovery Document Posting Plan (2016)

    Environment and Climate Change Canada’s Three-Year Recovery Document Posting Plan identifies the species for which recovery documents will be posted each fiscal year starting in 2014-2015. Posting this three year plan on the Species at Risk Public Registry is intended to provide transparency to partners, stakeholders, and the public about Environment and Climate Change Canada’s plan to develop and post these proposed recovery strategies and management plans. However, both the number of documents and the particular species that are posted in a given year may change slightly due to a variety of circumstances. Last update March 31, 2017