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Montana Field Guide

Montana Field Guides

Western Glacier Stonefly - Zapada glacier

Species of Concern
Native Species

Global Rank: G1
State Rank: S1
(see State Rank Reason below)

Agency Status


External Links

State Rank Reason (see State Rank above)
The Western Glacier Stonefly is currently ranked "S1" in Montana because it is thought to be at high risk due to very limited and/or potentially declining population numbers, range and/or habitat, making it extremely vulnerable to extirpation in the state. This species is particularly vulnerable due to it's very restricted habitat and cold water temperature requirements.
General Description
The Western Glacier Stonefly is a small, dark colored stonefly reported only within the habitats of glacial-fed streams in Glacier National Park, south to the Beartooth Mountains, and Teton National Park (Hotaling et al. 2017). This species is one of 7 species of globally-rare insects within Glacier National Park that may be adversely affected when the glaciers have completely melted.

In Montana, the adults have been collected in July (Baumann et al. 1977), and the larvae probably require at least 1 year to develop.

Diagnostic Characteristics
Larvae have not been associated with the adults or distinguished from other Z. oregonensis group species, although they share the typical characters of the group: cervical gills simple, unbranched and not constricted past the base (see photo of full view larva). Thus, this species would not be identified to species and left within this species group level by taxonomy labs identifying bioassesment samples. Adults described in Baumann and Gaufin (1971) (see photo of adult).

Species Range
Montana Range


Range Comments
Rangewide, Zapada glacier has been found in Glacier National Park, the Beartooth Mountains of southcentral Montana, and Teton National Park in Wyoming (Hotaling et al. 2017). It may also occur in Waterton Park, Alberta, but this has not yet been confirmed. Distribution of this species may be wider than currently known as it difficult to collect as it is found in glacier-fed streams at high elevations.

Observations in Montana Natural Heritage Program Database
Number of Observations: 42

(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)

This species occurs in steep (precipitous) glacial-influenced streams (Baumann et al. 1977).

Food Habits
The morphology of the mouthparts suggests that Zapada glacier is well-suited for shredding plant materials, thus trophic relationships would include being shredders and collectors-gatherers (detritus, CPOM) (Merritt and Cummins 1996).

Reproductive Characteristics
In Montana, the adults have been collected in July (Baumann et al. 1977).

On October 4, 2016 the U.S. Fish and Wildlife Service proposed listing the Western Glacier Stonefly under the Endangered Species Act due to primary threats to the habitat and range of this species including climate change, loss of glaciers and permanent snowfields, and changes in stream flow and water temperature. On November 21, 2019 a notice was published in the Federal Register that the species' status was determined to be Threatened. Further information on status can be found on the U.S. Fish and Wildlife Service's Species Account

Threats or Limiting Factors
With the increased evidence of global warming and melting glaicers in GNP, this species could be considered a candidate for the USFWS Threatened and Endangered species list.

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Citation for data on this website:
Western Glacier Stonefly — Zapada glacier.  Montana Field Guide.  .  Retrieved on , from