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Montana Field Guide

Montana Field Guides

A Rhyacophilan Caddisfly - Rhyacophila potteri

Species of Concern
Native Species

Global Rank: G3
State Rank: S2
(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 "S2" Species of Concern in MT and at risk because of very limited and/or potentially declining population numbers, range and/or habitat, making it vulnerable to extirpation in the state. Limited sites with small populations, and the species is difficult to identify without adult specimens.
  • Details on Status Ranking and Review
    A Rhyacophilan Caddisfly (Rhyacophila potteri) Conservation Status Review
    Review Date = 09/18/2008
    View State Conservation Rank Criteria
    Population Size

    ScoreU - Unknown


    Range Extent

    ScoreD - 1,000-5,000 km squared (about 400-2,000 square miles)

    Comment200-1000 km (125-620 miles) linear river

    Area of Occupancy

    Comment200-1000 km (125-620 miles) linear river

    Length of Occupancy

    ScoreLD - 200-1,000 km (about 125-620 miles)

    Long-term Trend

    ScoreE - Relatively Stable (±25% change)

    CommentSiltation and stream temperature increases with loss of riparian shading and lower snowpack probably contributed to some decline

    Short-term Trend

    ScoreE - Stable. Population, range, area occupied, and/or number or condition of occurrences unchanged or remaining within ±10% fluctuation


    ScoreG - Slightly threatened. Threats, while recognizable, are of low severity, or affecting only a small portion of the population or area.

    CommentClimate Change, increasing stream temperatures and lower snowpack could seriously impact the habitat that this speces exists in

    SeverityLow - Low but nontrivial reduction of species population or reversible degradation or reduction of habitat in area affected, with recovery expected in 10-50 years.

    ScopeLow - 5-20% of total population or area affected

    ImmediacyLow - Threat is likely to be operational within 5-20 years.

    CommentThreat is not fully operational now, but some areas have been lost.

    Intrinsic Vulnerability

    ScoreB - Moderately Vulnerable. Species exhibits moderate age of maturity, frequency of reproduction, and/or fecundity such that populations generally tend to recover from decreases in abundance over a period of several years (on the order of 5-20 years or 2-5 generations); or species has moderate dispersal capability such that extirpated populations generally become reestablished through natural recolonization (unaided by humans).

    Environmental Specificity

    ScoreC - Moderate. Generalist. Broad-scale or diverse (general) habitat(s) or other abiotic and/or biotic factors are used or required by the species but some key requirements are scarce in the generalized range of the species within the area of interest.

    CommentCold water stenotherm, cannot survive increases in water temperatures or will have to migrart to cooler temps

General Description
Rhyacophila potteri is a caddisfly that may have evolved from an isolated population of the R. verrula group along the Montana/Idaho border and southern British Columbia and Alberta. Perhaps because of ecological constraints such as temperature, R. potteri could have been confined to its present distribution in cold, mossy springs and seeps after glaciation.

Species Range
Montana Range


Range Comments
Known from Idaho, and recently Montana (Giersch 2002, Stagliano et al. 2007). Distribution data for U.S. states and Canadian provinces is known to be incomplete or has not been reviewed. It is likely that R. potteri has a continuous distribution along the Montana-Idaho border north to British Columbia and Alberta.

Observations in Montana Natural Heritage Program Database
Number of Observations: 14

(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)

Larval drift and adult movements not studied in Montana.

Collections of R. potteri have occurred at four localities in Montana, all of which are small streams or seeps with abundant mosses. This species is associated with moderate gradient, perennially flowing headwater springs and streams (Wiggins 1996).

Food Habits
The larva of this caddisfly are free-living, do not build a protective case and move actively to hunt for food, until just before pupation. The trophic relationship of Rhyachophila is usually predatory on other insects, especially chironomids (midge larvae) and simulids (blackfly larvae) (Merritt and Cummins 1996).

Not studied in Montana (but see Habitat comments).

Reproductive Characteristics
Not studied in Montana.

Limited data and the inability to identify larval collections has lead to a low global rank and a status of at risk (S2) in Montana. Distribution data for U.S. states and Canadian provinces is known to be incomplete or has not been reviewed for this taxon.

Threats or Limiting Factors
In general, cold-stenothermic. Cold-water specialist invertebrate populations are affected by changes to aquatic habitat, such as alteration of flow patterns, streambed substrate, thermal characteristics, and water quality. Alteration and degradation of riparian and aquatic habitat is the primary concern for Montana populations. Specific threats to Montana populations of R. potteri are primarily related to mismanagement of forested riparian areas especially during road-building and timber harvest activities, which can result in sediment and temperature increases.

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