Montana Field Guide

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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).

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.

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.

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).

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.