Species Profile

Sheathed Slug

Scientific Name: Zacoleus idahoensis
Taxonomy Group: Molluscs
Range: British Columbia
Last COSEWIC Assessment: April 2016
Last COSEWIC Designation: Special Concern
SARA Status: No schedule, No Status

Individuals of this species may be protected under Schedule 1 under another name; for more information see Schedule 1, the A-Z Species List, or if applicable, the Related Species table below.

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

Image of Sheathed Slug


Sheathed Slug is a small (20 – 24 mm long), slender slug with a keeled tail and longitudinal and oblique grooves on the sides and tail. The colour is solid grey or brownish grey. Small light flecks on the mantle and tail give the slug a bluish tint. Sheathed Slug is a regional endemic to moist forests of the northern Columbia Basin, an area that contains many unique plants and animals. (Updated 2017/01/24)


Distribution and Population

The global distribution of Sheathed Slug includes northern Idaho, northwestern Montana, and southeastern British Columbia. In British Columbia, Sheathed Slug occurs in scattered localities in the Kootenay region, south of 49°22’N within approximately 25 km of the Canada-United States border. Since the early 1990s, over 700 sites have been surveyed for terrestrial gastropods in the Kootenay region; recent surveys specifically targeted this species and other native slugs. There are records for the species from nine sites. The estimated range (extent of occurrence) of the species in Canada is 1,892 km2 based on these occurrences. (Updated 2017/01/24)



In British Columbia, Sheathed Slug has been found in mainly coniferous forest stands of varying ages, ranging from 40 – 50 years to old growth (>200 years old); most records are from shady, older forests. The slugs often inhabit riparian areas and gullies associated with small, fast-flowing tributary streams, seepage areas, or other very moist microsites. Moist microhabitats and refuges provided by decaying logs appear to be important. (Updated 2017/01/24)



The natural history of Sheathed Slug is poorly known. It is hermaphroditic (possessing both male and female reproductive organs) and lays eggs. Juveniles presumably overwinter, but the proportion of adults that do so is unknown. The generation time is probably 1 year or slightly more, based on the small body size of the adults and relatively short life spans of arionid slugs in general. The slugs feed on fungi and liverworts, and probably also on other live and decaying vegetation. Movement capabilities of Sheathed Slug are presumed to be low. Slugs in general are poor dispersers if not aided by humans, wind or water; no such passive means of dispersal are known for this species, exacerbating the effects of habitat fragmentation on its distribution within the landscape. (Updated 2017/01/24)



The greatest threats to Sheathed Slug populations in British Columbia are deemed to be logging, which continues to alter and fragment habitats, and droughts and flood events, the frequency and severity of which are predicted to continue to increase under climate change scenarios. Other threats include introduced invasive species, fire and fire suppression, roads, and livestock farming and ranching. Climate change and severe weather, fire and fire suppression, and forestry are likely to interact in a cumulative manner. Increased frequency and severity of prolonged summer droughts is expected to exacerbate the effects of logging (both recent and planned) and wildfires on the slug’s habitat, resulting in declines in both quantity and quality of habitat. (Updated 2017/01/24)



Federal Protection

Provincial and Territorial Protection

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



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.

4 record(s) found.

COSEWIC Status Reports

  • COSEWIC assessment and status report on the Sheathed Slug Zacoleus idahoensis in Canada (2017)

    Sheathed Slug is a small (20 - 24 mm long), slender slug with a keeled tail and longitudinal and oblique grooves on the sides and tail. The colour is solid grey or brownish grey. Small light flecks on the mantle and tail give the slug a bluish tint. Sheathed Slug is a regional endemic to moist forests of the northern Columbia Basin, an area that contains many unique plants and animals

Response Statements

  • Response Statement - Sheathed Slug (2017)

    In Canada, this slug is confined to a small area in the Kootenay region of southeastern British Columbia, generally within 25 km of the Canada-U.S. border. Most records are from older shady coniferous forest stands ranging from approximately 50 to >200 years. The species often inhabits riparian areas and other very moist microsites. Threats include logging and wood harvesting, and projected consequences of climate change including an increase in drought condition and wildfires. A decline is projected in the area, extent, and quality of habitat. The low number of scattered subpopulations makes the species vulnerable to both natural and human disturbances.

COSEWIC Annual Reports

  • COSEWIC Annual Report - 2015-2016 (2016)

    Over the past year COSEWIC re-examined the status of 25 wildlife species; of these, the majority (68%) were re-assessed at the same or lower level of risk. Of a total of 45 species assessed, seven were assigned a status of Not at Risk (two re-assessments and five new assessments). To date, and with the submission of this report, COSEWIC’s assessments now include 724 wildlife species in various risk categories, including 320 Endangered, 172 Threatened, 209 Special Concern, and 23 Extirpated (i.e., no longer found in the wild in Canada). In addition, 15 wildlife species have been assessed as Extinct, 54 wildlife species have been designated as Data Deficient, and 177 have been assessed and assigned Not at Risk status.

Consultation Documents

  • Consultation on Amending the List of Species under the Species at Risk Act: Terrestrial Species - January 2017 (2017)

    The Government of Canada is committed to preventing the disappearance of wildlife species at risk from our lands. As part of its strategy for realizing that commitment, on June 5, 2003, the Government of Canada proclaimed the Species at Risk Act (SARA). Attached to the Act is Schedule 1, the list of the species provided for under SARA, also called the List of Wildlife Species at Risk. Extirpated, Endangered and Threatened species on Schedule 1 benefit from the protection afforded by the prohibitions and from recovery planning requirements under SARA. Special Concern species benefit from its management planning requirements. Schedule 1 has grown from the original 233 to 521 wildlife species at risk. In 2016, on the recommendation of the Minister of the Environment, the Governor in Council approved listing proposals for 44 wildlife species. It is proposed that 23 species be added to Schedule 1, 18 be reclassified or have a change made to how they are defined (two wildlife species are being split into four), one species  be removed from Schedule 1, and another two species not be added. Listing proposals were published in Canada Gazette, part I for a 30-day public comment period and final listing decisions for all 44 species are expected in the first half of 2017.Please submit your comments byMay 11, 2017, for terrestrial species undergoing normal consultationsand byOctober 11, 2017, for terrestrial species undergoing extended consultations.For a description of the consultation paths these species will undergo, please see:Species at Risk Public Registry website The COSEWIC Summaries of Terrestrial Species Eligible for Addition or Reclassification on Schedule 1 - January 2017