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
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.
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.
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.
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.
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.
Provincial and Territorial Protection
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 (1 record(s) found.)
- Response Statements (1 record(s) found.)
- COSEWIC Annual Reports (1 record(s) found.)
- Consultation Documents (1 record(s) found.)
COSEWIC Status Reports
COSEWIC Annual Reports
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