CDC Logo

BC Conservation Data Centre: Species Summary


Prophysaon coeruleum
Blue-grey Taildropper

 
Scientific Name: Prophysaon coeruleum Cockerell, 1890
English Name: Blue-grey Taildropper
 
Classification / Taxonomy
Scientific Name - Concept Reference: Turgeon, D. D., J. F. Quinn, Jr., A. E. Bogan, E. V. Coan, F. G. Hochberg, W. G. Lyons, P. M. Mikkelsen, R. J. Neves, C. F. E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F. G. Thompson, M. Vecchione, and J. D. Williams. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society Special Publication 26, Bethesda, Maryland. 526 pp.
Classification Level: Species
Species Group: Invertebrate Animal
Species Code: MO-PROCOE
Kingdom Phylum Class Order Family
Animalia Mollusca Gastropoda Stylommatophora Arionidae
   
Conservation Status / Legal Designation
Global Status: G3G4 (Apr 2010)
Provincial Status: S2S3 (Feb 2024)
BC List: Blue
Provincial FRPA list:   
Provincial Wildlife Act:
COSEWIC Status: Threatened (Apr 2016)
SARA Schedule: 1  -  Threatened (Feb 2019)
General Status Canada:
   
Ecology & Life History
General Description:
Subspecies Comments: No subspecies are currently recognized, but genetic studies indicate both deep and shallow phylogenetic divisions across the species' range in western North America (Wilke and Duncan 2004). The BC population belongs to one of three major clades, the range of which extends from Vancouver Island south through the Cascade Mountains to south-central Oregon.
Identification Comments: Small, slender slug, with adult length up to 45 mm when extended in movement (Forsyth 2004). Distinguishing features include solid, blue or bluish-grey colouration, often with lighter flecking, and longitudinal, parallel grooves and ridges on the tail. The tone and brightness of the colour is variable. A thin, oblique constriction line is usually visible on the tail where self-amputation takes place, as also in other members of the genus Prophysaon.
Provincial Reproduction Comments: This species is oviparous and hermaphroditic (each individual possessing both male and female reproductive organs). Details of reproductive biology are unknown. No eggs or young have been found in BC to date.
Provincial Ecology Comments: The species exists at the northern extremity of its distribution in BC, and its northward and altitudinal range expansion may be limited by climatic factors. The species has been found only at low (less than 150 m asl) elevations in BC and seems to be restricted to coastal areas, whereas it occurs at higher elevations (up to 1650 m asl) farther south, in Oregon. Populations at the limits of a species' range may become important for the survival of the species under large-scale perturbations, such as climate change.
Migration Characteristics:
(Global / Provincial)		 
    Nonmigrant:
    Local Migrant:
    Distant Migrant:
    Within Borders Migrant: 		N / Y
N / N
N / N
na / N
Global Migration Comments: Dispersal abilities very limited, tens of hundreds of meters per generation (Wilke and Duncan, 2004).
Provincial Mobility & Migration Comments: Thought to be relatively sedentary with poor dispersal abilities (Wilke and Duncan 2004).
Habitats:
(Type / Subtype / Dependence) 		Forest / Conifer Forest - Moist/wet / Obligate
Forest / Mixed Forest (deciduous/coniferous mix) / Obligate
Global Habitat Comments: It inhabits moist, coniferous or mixed-wood forests of varying age classes (Wilke and Duncan, 2004; Kelley et al., 2009). All records from British Columbia are from within the Coastal Douglas fir biogeoclimatic zone while in Washington, it is often associated with older forests and required microhabitat features include abundant coarse woody debris or other cover, a deep forest litter layer, and shaded, moist forest floor conditions (COSEWIC, 2006).
Provincial Habitat Comments: Mature or maturing (>50 year old) mixed-wood forests with semi-open canopy that may contain Douglas-fir, Grand Fir, Western Red-cedar, and a deciduous component of Arbutus, Garry Oak, Bigleaf Maple, and/or Trembling Aspen (COSEWIC 2006, 2016r; Ovaska and Sopuck 2007d,e; ECCC 2018). Microhabitat features include abundant coarse woody debris, pockets of deep forest duff or moss, and moist forest-floor conditions.
Food Habits:
Global Food Habits Comments: Fungi found to be most common (90%) among food items (including fungi, vascular plant material, lichens, and imperfect fungi) although more plant material ingested in spring than in fall (McGraw et al., 2002).
Provincial Food Habits Comments: The slugs feed on fungi and plant material, but details of food habits of the BC population are lacking. Fungi form a major part of the diet, especially in the autumn, based on studies in Oregon (McGraw et al. 2002).
Global Phenology:
Provincial Phenology:
(1st half of month/
2nd half of month)
Provincial Phenology Comments: The slugs might be annual and over-winter as eggs, but little is known of the phenology of this species in BC or elsewhere (COSEWIC 2006). Presumably, eggs are laid in the autumn and hatch the following spring; young likely reach sexual maturity by the following autumn. All BC records represent observations of adult-sized slugs from October to early December (Ovaska and Sopuck 2007d,e).
Colonial Breeder: N
Length(cm)/width(cm)/Weight(g): / /
Elevation (m) (min / max): Global: 
Provincial:  25 / 120
   
 
Distribution
Endemic: N
Global Range Comment: It ranges from southern British Columbia south to Puget Lowlands in Washington and through the Cascade Range into Oregon and northern California (COSEWIC, 2006). This includes the Coast Range, Oregon and Washington Cascades, Puget Trough, Klamath Mountains of southwestern Oregon and northern California, western Idaho and southern Vancouver Island, British Columbia (Wilke and Duncan, 2004).
 
Authors / Contributors
Global Information Author: Cordeiro, J.
Last Updated: Apr 21, 2010
Provincial Information Author: Kristiina Ovaska
Last Updated: Jan 01, 2008
   
References and Related Literature
B.C. Ministry of Environment. Recovery Planning in BC. B.C. Minist. Environ. Victoria, BC.
COSEWIC 2006. COSEWIC assessment and status report on the Blue-grey Taildropper slug Prophysaon coeruleum in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 27 pp.
Forsyth, R.G. 2005. Comments on provisional ranks of British Columbia terrestrial molluscs. Unpubl. rep. submitted to the B.C. Minist. Sustainable Resour. Manage., Conservation Data Centre, Victoria, BC. 18pp.
McGraw, R., N. Duncan, and E. Cazares. 2002. Fungi and other items consumed by the blue-gray taildropper slug (Prophysaon coeruleum) and the papillose taildropper slug (Prophysaon dubium). The Veliger 45: 261-264 (Article not seen, citation from Forsyth, R.G. 2004. Land snails of British Columbia. University of British Columbia Press. Vancouver. 176pp.)
Ovaska, K. and L. Sopuck. 2008b. Surveys for the Blue-grey Taildropper and other gastropods at risk within the CRD Parks and Trails System in 2008. Report prepared for Capital Regional District (CRD) Parks, Victoria, BC. 70pp.
Ovaska, K. and L. Sopuck. 2007d. Surveys for the Blue-grey Taildropper within CRD parks and trails system in 2007. Progress report prepared for CRD parks. Victoria, BC. 14pp.
Ovaska, K. and L. Sopuck. 2007e. Surveys for the Blue-grey Taildropper slug (Prophysaon coeruleum) on federal lands on southern Vancouver Island, BC, fall 2007. Report Prepared by Biolinx Environmental Research Ltd. for CFS/CFB Esquimalt Natural Resources Program, Victoria, BC.
Wilke, T. and N. Duncan. 2004. Phylogeographical patterns in the American Pacific Northwest: lessons from the arionid slug Prophysaon coeruleum. Molecular Ecology 13: 2303-2315.
 

Please visit the website Conservation Status Ranks for definitions of the data fields used in this summary report.

Suggested Citation:

B.C. Conservation Data Centre. 2010. Species Summary: Prophysaon coeruleum. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 17, 2026).