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Montana Field Guide

Montana Field Guides

A Rhyacophilan Caddisfly - Rhyacophila ebria

Species of Concern

Global Rank: G2G3
State Rank: S1
* (see State Rank Reason below)

Agency Status
USFWS:
USFS:
BLM:


 

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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 high risk of extirpation in the state because of very limited and/or potentially declining population numbers, range and/or habitat. Limited sites with small populations, but these insects are also difficult to identify without adult specimens.
 
General Description
These caddisfly larvae are free-living forms that move actively around cobbles and boulders searching for food (predatory) without a case, until just before pupation. R. ebria is restricted to the northern Rocky Mountains, where it lives in cold alpine streams fed by permanent snowmelt, glaciers or icefields. Nimmo (1971) reported this species from small, turbulent creeks to tiny alpine trickles. Along with R. glaciera, this species occurs in the highest, coldest streams in Glacier National Park. Joe Giersch (personal observation) has collected R. glaciera pupating and emerging simultaneously with R. alberta. The trophic relationships of larvae of Rhyachophila are predatory on other insects, especially chironomid midges and simulidae (blackfly larvae) (Merritt and Cummins 1996).

Diagnostic Characteristics
See Denning 1949 for detailed adult description. Mature larval length is 10-11 mm. Head widest medially; as long as wide. Frontoclypeus with dark shading posteriorly, separate muscle scars distinct; maxillary palpus stout. Mandibles with a single apical tooth and abdominal segments are without gills like other members of this species group (Giersch 2002).

Species Range
Montana Range

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Range Comments
Originally described from Glacier Park, Logan Pass, Montana (Denning 1949; Newell and Potter 1973), but subsequently found in Manitoba and British Columbia (Mt. Revelstoke National Park) (Nimmo and Scudder 1978; Scudder 1994).

Summary of Observations Submitted for Montana
Number of Observations: 2

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Relative Density

Recency

 

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



Habitat
R. ebria is restricted to the northern Rocky Mountains, where it lives in cold alpine streams fed by permanent snowmelt, glaciers or icefields. Nimmo (1971) reported this species from small, turbulent creeks to tiny alpine trickles. Along with R. glaciera Denning, this species occurs in the highest, coldest streams in Glacier National Park. Joe Giersch (personal observation) has collected R. glaciera pupating and emerging simultaneously with R. alberta. These caddisfly larvae are free-living forms that move actively searching for food (predatory) with no case, until just before pupation. The trophic relationships of larvae of Rhyachophila are predatory on other insects, especially chironomid midges and simulidae (blackfly larvae) (Merritt and Cummins 1996).

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

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

Management
R. ebria 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 and Waterton, Banff, and Jasper National Parks of Alberta and British Columbia. With the increased evidence 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. ebria 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 communication), 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.

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