Species Profile

Blue-grey Taildropper

Scientific Name: Prophysaon coeruleum
Other/Previous Names: Blue-grey Taildropper Slug
Taxonomy Group: Molluscs
Range: British Columbia
Last COSEWIC Assessment: April 2016
Last COSEWIC Designation: Threatened
SARA Status: Schedule 1, Endangered

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

Image of Blue-grey Taildropper


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)



Federal Protection

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

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 Blue-grey Taildropper (Prophysaon coeruleum) in Canada [Proposed]
Status First 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.

12 record(s) found.

COSEWIC Status Reports

  • COSEWIC assessment and status report on the Blue-grey Taildropper slug Prophysaon coeruleum in Canada (2016)

    The Blue-grey Taildropper is one of nine described species of taildropper slugs (genus Prophysaon) endemic to western North America. It is a small- to medium-sized slug (up to 45 mm long when extended) with a slender body. Distinguishing external features include blue-grey colour and parallel grooves and ridges on the back and sides of the tail. Internally, the slugs are distinguished from related species by features of reproductive anatomy.

COSEWIC Assessments

Response Statements

  • Response Statement - Blue-grey Taildropper (2017)

    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)

    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.

Recovery Strategies

  • Recovery Strategy for the Blue-grey Taildropper (Prophysaon coeruleum) in Canada [Proposed] (2016)

    The Minister of the Environment and Climate Change is the competent minister for the Blue-grey Taildropper and has prepared the federal component of this recovery strategy (Part 1), as per section 37 of SARA. It has been prepared in cooperation with the Province of British Columbia. SARA section 44 allows the Minister to adopt all or part of an existing plan for the species if it meets the requirements under SARA for content (sub-sections 41(1) or (2)). The British Columbia Ministry of the Environment led the development of the attached recovery plan for the Blue-grey Taildropper (Part 2) in cooperation with Environment and Climate Change Canada.


  • 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.
  • 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: 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.
  • 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

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