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Montana Field Guide

Montana Field Guides

Rocky Mountain Duskysnail - Colligyrus greggi

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Species of Concern
Native Species

Global Rank: G4
State Rank: S1
(see State Rank Reason below)

Agency Status

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State Rank Reason (see State Rank above)
Due to this restricted distribution and few known occurrences, this species has been placed on the MT Species of Concern list as S1, critically imperiled and extremely vulnerable to extirpation in the state. Only a few occurrences known despite extensive sampling in its preferred habitats in the past few years; restrictive spring-influenced habitats.
General Description
A very small, cold-water Hydrobiid snail restricted to cold freshwater streams and springs. Both known localities for this species in Utah are rheocrenes, springs flowing from the ground as streams. The Montana sites are small forested streams with extensive groundwater/spring inputs.

Diagnostic Characteristics
This is a small, moderately high conic snail (Frest and Johannes 1995) and is the only Hydrobiid in the western cold water streams in Montana.

Species Range
Montana Range


Range Comments
Limited to far western and southwestern MT. Known from western Montana, southeastern Idaho, and western Wyoming in the Snake River, Bear River, and Clark Fork River drainages (Frest and Johannes 1995). This is similar to Burch's (1989) assessment of Cliff Creed Canyon, 30 miles south of Jackson, Wyoming (Snake River drainage), and western Montana and southeastern Idaho.

Observations in Montana Natural Heritage Program Database
Number of Observations: 4

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)


Inhabits cold freshwater streams and springs. Both known localities for this species in Utah are rheocrenes, springs flowing from the ground as streams. The temperature at one of the springs was 5 C. At the other locality, the temperature was 8 C and the conductivity was 290 micromhos/cm (Hershler 1999). The reported streams in Montana are cold (8-12 C), forested, 2-3m wetted width, and moderate gradient sites in the Pacific refugium part of the state.

Food Habits
Like most Hydrobiid snails, they are likely scrapers and eaters of algae and diatoms.

Colligyrus greggi are cold water stenotherms and do not tolerate warm water temperatures (greater than 12 degrees C as the maximum annual temperature).

This species is quite rare in WY and MT, but may be relatively more common in southeastern ID. Other factors include loss of historic sites, specialized habitat, modification and loss of that habitat, and occurrence on public lands (Frest and Johannes 1995).

Threats or Limiting Factors
Threats to this species would be the increasing water temperatures brought on by forest harvesting too close to the riparian areas of the streams they inhabit. Many occupied sites are threatened at the local level by agricultural run-off, small dams, and campgrounds (Frest and Johannes 1995).

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Citation for data on this website:
Rocky Mountain Duskysnail — Colligyrus greggi.  Montana Field Guide.  .  Retrieved on , from