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Montana Field Guide

Montana Field Guides

Cascades Stripetail - Cascadoperla trictura

Native Species

Global Rank: G3G4
State Rank: SNR

Agency Status


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General Description
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Diagnostic Characteristics
Adult male morphology: Body length is 8-9 mm. Macropterous , having forewing length 8-9.5 mm. General body color is yellow to light brown. A round black spot covers the interocellar area of head and continues to the anterior margin of frons. Pronotum is light yellow with a median light stripe bordered by 2 longitudinal dark brown bands containing vermiform rugosities. Wings are hyaline with veins medium brown. Abdominal terga have 3 longitudinal dark brown stripes and 8 rows of longitudinal dots (Szczytko and Stewart 1979).

Mature larval morphology (reared larvae): Length of mature male is 9.1-10.3 mm; length of mature female larva is 10.2-12.6 mm. Interocellar area of head is medium brown, wide, with a dark brown pigment band extending across the frons; the anterior margin has a narrow light, transverse band and a row of small, stout spinulae on the occipital ridge. The pronotal margin is fringed with small, stout hairs and with numerous long hairs irregularly placed at the upper and lower angles and posterior margin. Pronotum has a medial light yellow stripe bordered by 2 wide, medium brown longitudinal bands; rugosities absent; light narrow band on the lateral and posterior margins (Szczytko and Stewart 1979).

Range Comments
The distribution includes British Columbia, Washington, Oregon, California, Idaho, and Montana (Szczytko and Stewart 1979). In Idaho, the species is known from one collection site: Coeur d’Alene River, Kingston, Shoshone County (Baumann personal communication 2005). In Montana, this species is known from one stream in 2 collections, Ninemile Creek, Missoula County (Stagliano, this study 2006).

Observations in Montana Natural Heritage Program Database
Number of Observations: 2

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Relative Density



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

Found in creeks and rivers (Baumann et al. 1977; Szczytko and Stewart 1979). Merritt and Cummins (1996) report the habit of this species as “clingers and crawlers" and like most Perlodidae are predators, consuming other insects, especially midges and blackflies.

Food Habits
Merritt and Cummins (1996) report that members of the families, Perlidae and Perlodidae, are largely predators eating other aquatic invertrebrates, especially Diptera (Chironomidae and Simuliidae, midges and blackflies) and Mayflies.

Reproductive Characteristics
Based on material examined by Szczytko and Stewart (1979), emergence occurs from mid-May until July in creeks and rivers. Baumann, Gaufin, and Surdick (1977) report that adults emerge from April to July.

The species is known from a single collection in Idaho (Baumann personal communication 2005, Szczytko and Stewart 1979) and a single stream in Montana (Stagliano, this study 2006).

Threats or Limiting Factors
Specific threats to MT/ID populations of C. trictura have not been identified. In general, stonefly populations are affected by alterations of aquatic habitat such as changes of flow patterns, streambed substrate, thermal characteristics, and water quality. Degradation of aquatic habitat is the primary concern for any population.

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Citation for data on this website:
Cascades Stripetail — Cascadoperla trictura.  Montana Field Guide.  .  Retrieved on , from