Capniidae - Description and Ecology

Description and Ecology

Adult Capniidae, as their common name implies, typically small Plecoptera; while most are less than 1 cm long with some measuring just 4 mm as adults, a few are as large as 25 mm (1 inch) at adulthood. The adults emerge from the water in winter and are often found walking around on the snow. Characteristic are the wings with at most one cubital crossvein, and the paraprocts (anal lobes) whose inner lobes form a tube closed on the underside by the outer lobes.

Nymphs of small winter stoneflies typically have a very elongated and slender body, similar to those of rolled-winged stoneflies (Leuctridae). However, the groove along the abdomen, from segment 1 to 9, is generally very pronounced.

The nymphs dwell in the hyporheic zone, the interface between stream water and groundwater. Only immediately before moulting into the adult form will the nymphs move out of the substrate and appear on the stream bed. Thus, although they may be plentiful in clean rivers and streams, they are seldom encountered in standard samples of benthos.