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Montana Field Guide

Montana Field Guides

Northern Rocky Mountains Refugium Caddisfly - Rossiana montana

Species of Concern
Native Species

Global Rank: G2G3
State Rank: S2
(see State Rank Reason below)

Agency Status

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State Rank Reason (see State Rank above)
This NRMR 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 specialized habitats. This species is a rare, endemic caddisfly only found in specific streams in the Pacific Influenced areas of Montana and Idaho (referred to as the Northern Rocky Mountian Refugium).
  • Details on Status Ranking and Review
    Northern Rocky Mountains Refugium Caddisfly (Rossiana montana) Conservation Status Review
    Review Date = 09/18/2008
    Population Size

    ScoreU - Unknown


    Range Extent

    ScoreB - 100-250 km squared (about 40-100 square miles)

    Comment<100-250 square km (less than about 40-100 square miles)

    Area of Occupancy

    Comment40-200 km (25-125 miles) linear river

    Length of Occupancy

    ScoreLC - 40-200 km (about 25-125 miles)

    Long-term Trend

    ScoreD - Moderate Decline (decline of 25-50%)

    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


    ScoreF - Widespread, low-severity threat. Threat is of low severity but affects (or would affect) most or a significant 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.

    ScopeModerate - 20-60% 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

    ScoreC - Not Intrinsically Vulnerable. Species matures quickly, reproduces frequently, and/or has high fecundity such that populations recover quickly (< 5 years or 2 generations) from decreases in abundance; or species has high dispersal capability such that extirpated populations soon become reestablished through natural recolonization (unaided by humans).

    Environmental Specificity

    ScoreB - Narrow. Specialist. Specific habitat(s) or other abiotic and/or biotic factors (see above) are used or required by the Element, but these key requirements are common and within 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
The larvae of the caddisfly Rossiana montana occurs in high-gradient, 1st or 2nd order, perennially flowing, forested springs and streams (especially in gravel under mossy areas) of the Rocky Mountain Refugium Area (ID/MT boundary area). The ecological system this species is most closely associated with is referred to as the Northern Rocky Mountain Refugium Headwater Forested Streams. The small rock larval case of Rossiana makes it somewhat distinctive compared to other caddisfly families and only another rare caddisfly, Goeoriella (Rossianidae) should be confused with it while sampling in these areas.

Pupae and late-instar larvae were collected in June, so adults may be flying from late-June to July.

Diagnostic Characteristics
Morphology of adults is described by Denning 1973. Larval body length up to 10 mm. They are unusual case-makers (see photo) and the posteriolateral margins of the head are extended as prominent flanges. The head and pronotal areas are brownish-red and coarsely pebbled. Mandibles have separate tooth-like points.

Species Range
Montana Range Range Descriptions


Range Comments
Rangewide, Rossiana montana is a regional endemic only known to occur in western Montana, Washington, and British Columbia (Wiggins 1996, NatureServe 2015). In Montana, Rossiana montana has been reported from streams in Missoula, Mineral and Sanders counties (Stagliano et al. 2007). Rossiana montana has not been reported in Idaho yet, but it is likely to be found in the NRMR area (Clearwater National Forest) near the MT border.

Observations in Montana Natural Heritage Program Database
Number of Observations: 11

(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.

This species is associated with high-gradient, 1st or 2nd order, perennially flowing springs and streams, especially in gravel under mossy areas (Wiggins 1996, Stagliano et al. 2007).

Food Habits
Not studied in Montana.

The trophic relationship of larvae of R. montana includes scrappers and shredders (eating detritus & larger plant materials) (Merritt and Cummins 1996, Wiggins 1996).

Reproductive Characteristics
Pupae and late-instar larvae were collected in June, so adults may be flying from late-June to July.

Rossiana montana has been described as a rare species due to habitat specificity and is never abundant when collected (Wiggins 1996, Stagliano et al. 2007). It has no USFWS status at the present time, although it is currently a USFS Species of Concern (SOC). It is ranked globally at risk/potentially at risk (G2G3) by Natureserve (2015), and at risk (S2) in Montana, although not yet reported for Idaho.

Threats or Limiting Factors
Specific threats to Montana populations of R. montana would include mismanagement of forested riparian areas, including sediment and temperature increases associated with road building and timber harvests not following BMPs. In general, cold-stenothermic (cold-water specialists) invertebrate populations can be affected by slight changes to the thermal characteristics of their aquatic habitats, such as alteration of flow patterns, increased sunlight exposure, streambed substrate and water quality. Alteration and degradation of riparian and aquatic habitat is the primary concern for these populations.

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Citation for data on this website:
Northern Rocky Mountains Refugium Caddisfly — Rossiana montana.  Montana Field Guide.  .  Retrieved on , from