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Montana Field Guide

Montana Field Guides

Alberta Snowfly - Isocapnia integra

Species of Concern
Native Species

Global Rank: G4G5
State Rank: S2
(see State Rank Reason below)

Agency Status

External Links

State Rank Reason (see State Rank above)
The Alberta snowfly is currently ranked "S2" in Montana because it was thought to be at risk due to very limited and/or potentially declining population numbers, range and/or habitat, making it vulnerable to extirpation in the state. But, recent range extensions due to taxonomic changes may warrant re-evaluating this SOC rank.
  • Details on Status Ranking and Review
    Alberta Snowfly (Isocapnia integra) Conservation Status Review
    Review Date = 09/18/2008
    Population Size

    ScoreU - Unknown


    Range Extent

    ScoreU - Unknown

    Area of Occupancy

    CommentLB = 4-40 km (about 2.5-25 miles)

    Length of Occupancy

    ScoreLB - 4-40 km (about 2.5-25 miles)

    Long-term Trend

    ScoreE - Relatively Stable (±25% change)

    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.

    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.

    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

    ScoreA - Very Narrow. Specialist. Specific habitat(s), substrate(s), food type(s), hosts, breeding/nonbreeding microhabitats, or other abiotic and/or biotic factor(s) are used or required by the Element in the area of interest, with these habitat(s) and/or other requirements furthermore being scarce within the generalized range of the species within the area of interest, and, the population (or the number of breeding attempts) expected to decline significantly if any of these key requirements become unavailable.

General Description
Species within the Capniidae are small winter stoneflies. This family is one of the largest families in the order Plecoptera, containing some 300 species distributed throughout the Holarctic region, 25 species occur in Montana. As their name implies these species are generally cold-water stenotherms and hatch in late-winter through early spring. The adults emerging in the winter are often found walking around on the snow. Their closest relatives are the Rolled-winged Stoneflies (Leuctridae). Many species are endemic to small ranges, perhaps due to the family's tendency to evolve tolerance for cold (isolating populations in mountain valleys) and winglessness (inhibiting dispersal).

Adults are usually flying from late-April to May and into June.

Diagnostic Characteristics
Larvae cannot be identified to species and adults are rarely collected by summer sampling. Isocapnia fraseri and I. missourii are synonymized with I. integra (Zenger and Baumann 2004). Isocapnia missourii (taxon) has been removed from the central database and collection records are now displayed as I. intregra.

Species Range
Montana Range Range Descriptions


Range Comments
Rangewide, the species is found from the northern Rocky Mountains (extends north to the northeastern coast of Alaska, west into Alberta), and east to western South Dakota. While it once seemed restricted to the North Fork Flathead (MT) and Banff National Park, with the taxonomic revision to include Isocapnia missourii, it has expanded is range in Montana to the SW part of the state and the east side of the continental divide and over to the Black Hills of western SD.

Observations in Montana Natural Heritage Program Database
Number of Observations: 25

(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 is not known to migrate and in fact, the males are sometimes "apterous" or "micropterous" and cannot fly.

Very little information exists about the ecology of this species (Baumann et al. 1977). Collections have found this species in small streams and large rivers. Early records reported members of this species to be found in Banff National Park and North Fork Flathead River which are coldwater systems, but additional records have found them in transitional cold-cool water systems (Smith River, Missouri river). These stoneflies are trophically shredder-detritivores.

Food Habits
Merritt and Cummins (1996) report that members of this family are trophically shredder-detritivores; eating large particulate organic materials such as detritus, leaves and plants.

These stoneflies are probably cold water stenotherms.

Reproductive Characteristics
Adults are typically flying in May and June.

No management plan is in place, but more targeted sampling in early spring is recommended to fully understand this species' distribution, as it may be more widespread than previously thought.

Threats or Limiting Factors
Listed as a rare species when found, never abundant. Larvae cannot be identified to species and adults are rarely collected by biomonitoring agencies, thus few records exist.

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Citation for data on this website:
Alberta Snowfly — Isocapnia integra.  Montana Field Guide.  .  Retrieved on , from