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Montana Field Guide

Montana Field Guides

A Rhyacophilan Caddisfly - Rhyacophila glaciera

Species of Concern

Global Rank: G3
State Rank: S1
(see State Rank Reason below)

Agency Status


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State Rank Reason (see State Rank above)
This Rhyacophilan Caddisfly is currently ranked a "S1" Species of Concern in MT and is at extreme risk of becoming extirpated in the state because of very limited and/or potentially declining population numbers, range and/or habitat. Limited sites with small populations, retreating glaciers and the difficultly of identifying this species without adult specimens all contribute to its state threatened status.
General Description
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Diagnostic Characteristics
Adult morphology: Forewing 8-9.5 mm, transparent yellowish with some cross-veins surrounded with smoky brown, giving them a gray speckled appearance on apical half. Head brown, setal warts lighter. Antennae brown. Legs yellowish brown, tibiae lighter apically (see Denning 1965 for detailed adult description).

Larval morphology: Mature larvae are ~10 mm. Posterior margin of frontoclypeus with dark pattern, obscuring distinct muscle scars. Head wedge shaped, narrowing in anterior half, light brown with darkened muscle scars, darker areas laterally; posterior margin of frontoclypeus with dark shading, separate muscle scars indistinct; maxillary palpus stout, second segment slightly longer than first; left mandible with single apical tooth, right mandible with three apical teeth, one small mesal tooth. Pronotum brown with several darkened muscle scars posteriorly (Giersch 2002).

Species Range
Montana Range

All Ranges
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Range Comments
R. glaciera is a regional endemic only known to occur in high alpine snowmelt and spring fed streams along the Rocky Mountain Cordillera in Glacier National Park of Montana, Waterton, Banff and Jasper National Parks of Alberta, and British Columbia (Wiggins 1996, NatureServe 2015). This distribution may be associated with a glacial refugium in the area. In Montana, R. glaciera is unlikely to occur outside of Glacier National Park (Glacier and Flathead Counties) and thus, has little management implications at the Northern Region 1 Forest Service level.

Observations in Montana Natural Heritage Program Database
Number of Observations: 20

(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)

R. glaciera is isolated to the northern Rocky Mountains, where it lives in cold alpine streams fed by permanent snowmelt or ice fields. Nimmo (1971) reported this species from small, turbulent creeks to tiny alpine trickles, Along with R. ebria Denning, this species occurs in the highest, coldest streams in Glacier National Park. This species has also been collected with R. glaciera pupating and emerging simultaneously with R. alberta (J. Giersch, personal observation).

Food Habits
Most Rhyacophila species are free-living predators feeding mostly on aquatic insects, especially midges and blackflies.

Reproductive Characteristics
In Montana, adults have been collected from mid-August through early October.

R. glaciera is a regional endemic only known to occur in high alpine snowmelt and spring fed streams along the Rocky Mountain Cordillera in Glacier National Park of Montana, Waterton, and Banff and Jasper National Parks of Alberta and British Columbia. With the increased advancement of global warming, this species could be considered a candidate for the USFWS Threatened and Endangered species list.

Threats or Limiting Factors
Specific threats to Montana populations of R. glaciera would include global warming and the melting of glaciers. If the existing glaciers disappear from Glacier National Park, as predicted in 25 years (2030-2040)(D. Fagre personal communnication), this species will likely be extirpated from the state and possibly extinct. In general, cold-stenothermic (cold-water specialists) invertebrate populations are affected by changes to aquatic habitat, such as alteration of flow patterns, streambed substrate, thermal characteristics, and water quality.

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Citation for data on this website:
A Rhyacophilan Caddisfly — Rhyacophila glaciera.  Montana Field Guide.  .  Retrieved on , from