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Hooked Snowfly - Isocapnia crinita
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State Rank Reason (see State Rank above)
The Hooked 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 newly reported collections may warrant re-evaluating this SOC rank.
Details on Status Ranking and Review
Hooked Snowfly (Isocapnia crinita ) Conservation Status Review
Population Size
Score U - Unknown
Comment Unknown.
Range Extent
Score U - Unknown
Area of Occupancy
Comment LB = 4-40 km (about 2.5-25 miles)
Length of Occupancy
Score LB - 4-40 km (about 2.5-25 miles)
Long-term Trend
Score E - Relatively Stable (±25% change)
Short-term Trend
Score E - Stable. Population, range, area occupied, and/or number or condition of occurrences unchanged or remaining within ±10% fluctuation
Threats
Score F - Widespread, low-severity threat. Threat is of low severity but affects (or would affect) most or a significant portion of the population or area.
Severity Low - Low but nontrivial reduction of species population or reversible degradation or reduction of habitat in area affected, with recovery expected in 10-50 years.
Scope Moderate - 20-60% of total population or area affected
Immediacy Low - Threat is likely to be operational within 5-20 years.
Intrinsic Vulnerability
Score B - 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
Score A - 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).
Phenology
Adults are emerging in March-May.
Diagnostic Characteristics
Larvae cannot be identified to species and adults are rarely collected during summer sampling.
Species Range
Montana Range
Range Descriptions
Native
Range Comments
Rangewide, the species is known from Alaska (SNR), Montana (S2), Idaho, New Mexico (SNR), Colorado, Utah (S1S2), Manitoba (SNR), Saskatchewan (SNR), and the Yukon Territory (SNR).
Observations in Montana Natural Heritage Program Database
Number of Observations: 22
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Map Help and Descriptions
Relative Density
Recency
(Observations spanning multiple months or years are excluded from time charts)
Habitat
Very little information exists about the ecology of this species (Baumann et al. 1977). Merritt and Cummins (1996) report that members of the genus Isocapnia are found in both creeks and rivers and 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.
Ecology
These stoneflies are probably cold water stenotherms.
Reproductive Characteristics
Adults are emerging in March-May.
Management
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.
Stewardship Responsibility
Threats or Limiting Factors
Listed as a rare species when found; never abundant. Adults are rarely collected by biomonitoring agencies and few records exist.
References
Literature Cited AboveLegend: Plecoptera ) of the Rocky Mountains. American Entomological Society, Philadelphia.
Additional ReferencesLegend: Do you know of a citation we're missing? Isocapnia , with an emphasis on the North American fauna (Plecoptera: Capniidae). Monographs of the Western North American Naturalist 2(1):65-95.
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