Agapetus Caddisfly larva

Description:

Agapetus montanus is a caddisfly in the family Glossosomatidae (saddle case or tortoise case-makers). Larva can reach up to 6 mm and construct a case from small fragments of rock and sand grains that resemble a tortoise shell. The case has a rounded top and a "strap" beneath that creates two openings on the ventral surface through which the larva carries the case. At each successive larval instar a new, larger case is formed until finally the case is removed, attached to the substrate, and pupation occurs within it. Larvae of A. montanus generally construct cases that have larger rocks along the edge.

Habitat:

Found in Iowa, Montana, and Manitoba. The larvae of A. montanus occur on the upper surfaces and sides of rocks and boulders in moderate gradient, fast flowing, foothill to mountain streams. The riparian canopy of the streams where the larvae can be found are predominantly open and exposed to sunlight. They are easily spotted in a clear stream as they go about grazing on algae and diatoms from the surfaces of the nearby rocks. A. montanus is the only known species in this genus to be found in Montana.

Notes:

A. montanus has no federal status at present but is listed as a US Forest Service Species of Concern (SOC) in the Bitterroot, Flathead, and Lolo National Forests in Montana, and is listed as endangered in Idaho and vulnerable to extirpation in Montana.