Scientific Name: Prophysaon coeruleum
Other/Previous Names: Blue-grey Taildropper Slug
Taxonomy Group: Molluscs
COSEWIC Range: British Columbia
COSEWIC Assessment Date and Status Change: April 2016
COSEWIC Status: Threatened
COSEWIC Status Criteria: B1ab(iii)+2ab(iii)
COSEWIC Reason for Designation: This small, slender blue-coloured slug is only found in western North America where it lives in the moist layer of fallen leaves and mosses in mixed-wood forest. In Canada, it is confined to the southeastern tip of Vancouver Island within the Coastal Douglas-fir biogeoclimatic zone and where it transitions into the Coastal Western Hemlock biogeoclimatic zone. These habitats are declining in extent and what remains is becoming increasingly fragmented. Fifteen subpopulations are currently known, an increase that has resulted in a change of status. A continuing decline in habitat quality is expected due to natural ecosystem modification and competition with invasive species as well as droughts and severe weather events from climate change.
COSEWIC History of Status Designation: Designated Endangered in April 2006. Status re-examined and designated Threatened April 2016.
SARA Status: Schedule 1, Threatened
Date of Listing (yyyy-mm-dd): 2007-12-13
Please note that this information is provided for general information purposes only. For the most up to date and accurate list of species listed under the Species at Risk Act, please see the Justice Laws Website.
Blue-grey Taildropper (Prophysaon coeruleum) is a small slender slug (Arionidae: Anadeninae) with adults measuring between 20 – 40 mm in length. Distinguishing features include solid blue-grey colour without stripes and distinct, parallel grooves and ridges on the back and sides of the tail. As in other taildroppers (genus Prophysaon), a thin, oblique constriction or impressed line is usually visible on the tail at the site where autotomy (self-amputation) takes place, if the slug is attacked by a predator. Blue-grey Taildropper may act as a dispersal agent for spores of fungi that form symbiotic associations with tree roots, thereby performing an important ecological function. (Updated 2016/12/15)
Distribution and Population
Blue-grey Taildropper is endemic to western North America, where it occurs from southwestern British Columbia south through the Puget Lowlands and Cascade Range of Washington State into Oregon and northern California; a disjunct population exists in northern Idaho. In Canada, Blue-grey Taildropper is documented only from southern Vancouver Island, where 15 subpopulations are known. All but two records are from within the Capital Regional District. In 2013, the species was found in the North Cowichan District, approximately 28 km north of the nearest record, followed by a second observation in the general area in 2015. The estimated range (extent of occurrence) of Blue-grey Taildropper in Canada has increased from 150 km² to 658 km² since the previous status report, reflecting increased search effort over the past decade. Undocumented localities probably exist, but it is highly unlikely that there would be large additions to their range given the extensive search effort on southern Vancouver Island; hundreds of localities have been searched for terrestrial gastropods on Vancouver Island and the adjacent coastal mainland of British Columbia. (Updated 2016/12/15)
Blue-grey Taildropper inhabits low-elevation (less than 250 m above sea level) mature or maturing second growth mixed-wood forest (greater than 60 years old) on the drier southeastern tip of Vancouver Island within the Coastal Douglas-fir biogeoclimatic zone and where it transitions into the Coastal Western Hemlock biogeoclimatic zone. These habitats are declining rapidly in extent and becoming seriously fragmented due to urban and rural development. The Coastal Douglas-fir biogeoclimatic zone is one of the most disturbed ecosystems of British Columbia. This zone contains several rare and provincially listed Douglas-fir, Garry Oak and Arbutus ecosystems, where Blue-grey Taildropper has been found, although it is not restricted to these habitats. The slugs are patchily distributed within the landscape. Small forest gaps and woodland habitats may be favoured over deeper forest at the northern limits of the species’ distribution, as they capture the sun and provide relatively warm forest floor conditions. Availability of suitable moist refuges, such as provided by abundant coarse woody debris and/or a deep moss layer, is thought to be important. (Updated 2016/12/15)
Blue-grey Taildropper appears to have an annual life cycle, maturing and reproducing within one year and overwintering as eggs. In British Columbia, juveniles have been observed in April – June, while almost all adults have been found in September – December; one adult was found in March, indicating successful overwintering by at least some adults. Blue-grey Taildropper feeds extensively on fungi. A variety of vertebrate and invertebrate predators, native and introduced, prey on slugs and probably also on this species. Blue-grey Taildropper is capable of self-amputation of the tail, an adaptation that is an effective anti-predation mechanism against some predators. Blue-grey Taildroppers are thought to have very limited dispersal capabilities, in the order of tens to hundreds of metres per generation. (Updated 2016/12/15)
Blue-grey Taildropper exists at the northern extremity of its geographic range in southwestern British Columbia. Low dispersal ability and requirements for moist habitats limit the speed with which the slugs can colonize new habitats or habitat patches from which they have become extirpated. Main threats to Blue-grey Taildropper are from natural ecosystem modification by non-native invasive plants, competition and predation by introduced invertebrates, and from droughts associated with climate change and severe weather. Introduced invasive plants are prevalent at many Blue-grey Taildropper sites on Vancouver Island and deteriorate habitat quality by displacing native plants and altering the microclimate and possibly food supply for slugs. Non-native gastropods and other invertebrates, such as ground beetles (Coleoptera: Carabidae) pose a threat through predation and through competition for food and shelter. Prolonged and more frequent droughts are expected to reduce survivorship and length of time available for foraging and growth. Such effects can be expected to be particularly severe in degraded habitat patches that may lack microhabitats suitable for refuges. Other widespread threats include recreational activities and expanding housing and urban developments that contribute to habitat loss and degradation. (Updated 2016/12/15)
The Blue-grey Taildropper 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.
Provincial and Territorial Protection
Status of Recovery Planning
Recovery Strategies :
Name Recovery Strategy for the Blue-grey Taildropper (Prophysaon coeruleum) in Canada
Status Final posting on SAR registry
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.
14 record(s) found.
- COSEWIC Status Reports (1 record(s) found.)
- Response Statements (2 record(s) found.)
- Recovery Strategies (1 record(s) found.)
- Orders (4 record(s) found.)
- COSEWIC Annual Reports (2 record(s) found.)
- Consultation Documents (2 record(s) found.)
- Related Information (1 record(s) found.)
- Recovery Document Posting Plans (1 record(s) found.)
COSEWIC Status Reports
Response Statement - Blue-grey Taildropper (2017-01-11)This small, slender blue-coloured slug is only found in western North America where it lives in the moist layer of fallen leaves and mosses in mixed-wood forest. In Canada, it is confined to the southeastern tip of Vancouver Island within the Coastal Douglas-fir biogeoclimatic zone and where it transitions into the Coastal Western Hemlock biogeoclimatic zone. These habitats are declining in extent and what remains is becoming increasingly fragmented. Fifteen subpopulations are currently known, an increase that has resulted in a change of status. A continuing decline in habitat quality is expected due to natural ecosystem modification and competition with invasive species as well as droughts and severe weather events from climate change.
Response Statements - Blue-grey Taildropper Slug (2006-11-29)This species has a very small extent of occurrence (~ 150 km2) and area of occupancy (< 5 km2), and a continuing decline is projected in quality of habitat. It is found in remnant patches of older forest with a deciduous component. It is currently known from only 5 locations on southern Vancouver Island. Threats at these locations include heavy recreational use and the impacts of introduced plants and animals, including introduced invasive slugs and snails.
COSEWIC Annual Reports
COSEWIC Annual Report - 2006 (2006-08-30)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.
COSEWIC Annual Report - 2015-2016 (2016-10-13)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.