Montana Field Guide

This is a large, swimming, wetland and slow current mayfly with a minnow-like body and large gills along the abdomen. These could be predaceous mayflies given the modified structures of the labial palps (almost raptorial). They hatch during early spring (snow -melt) from dormant eggs laid the previous spring, and have a brief, rapid growing nymphal period until adults hatch in late-spring early summer
(Edmunds 1957).

Labial palps of the larvae with pincer-like ends; gills on all abdominal segments are heart-shaped and single, other members of this family can have double gills; abdominal segments with prominent posterolateral projections (see figure).

Larvae are found in temporary ponds and fringe wetlands on the edges of lakes in association with heavy growth of broad-leaved sedges (Carex spp.). The habitat and biology of this species has been well documented (Edmunds 1957). Ironically, the species appears to be extirpated in the high-mountain Carex-wetland area of Utah where the species was studied in detail. Records from the 1960s exist for Idaho but intensive surveys recently found no specimens, and older historical records exist for British Columbia and Wyoming. The current global ranking appears warranted at this time. In Washington, it potentially could occur in Stevens Co. in Chamokane Creek because it is known from adjacent British Columbia (Meyer and McCafferty 2007). The larvae are often concentrated where a slight current exists (Edmunds 1957). In addition to lakes and ponds, this species occurs at the slack-water edges of moderately flowing rivers and streams (Jensen 1966).

These could be predaceous mayflies given the modified structures of the labial palps allowing them to prey on other wetland invertebrates.

Merritt and Cummins (1996) consider larvae to be swimmers and climbers. These could be predaceous mayflies given the modified structures of the labial palps. Larvae are found in ponds and fringe wetlands on the edges of lakes in association with heavy growth of broad-leaved sedges (Carex spp.). The habitat and biology of this species has been well documented (Edmunds 1957). Ironically, the species appears to be extirpated in the high-mountain Carex-wetland area of Utah where the species was studied in detail. Records from the 1960s exist for Idaho but intensive surveys recently found no specimens, and older historical records exist for British Columbia and Wyoming. The current global ranking appears warranted at this time. The larvae are often concentrated where a slight current exists (Edmunds 1957). In addition to lakes and ponds, this species occurs at the slack-water edges of moderately flowing rivers and streams (Jensen 1966). Males were observed swarming high in the air over a small glacial stream with females flying over the water (McDunnough 1938).

Eggs are deposited by females in wetlands and pools in mid-June. Eggs remain dormant during the summer and winter and “hatch within one day after the snow melts the next May.” Larvae have an extremely short development period compared to other mayfly species. Larvae crawl “out of the water one or two inches onto a Carex leaf, and the subimago emerges and flies high into a tree” (Edmunds 1957). Larvae that were wild-caught and reared in the laboratory developed into subimagoes in early to mid-June. The larval stage was less than 2 weeks (Edmunds 1957). Males were observed swarming high in the air over a small glacial stream with females flying over the water (McDunnough 1938).

Insignificant threats to the Glacier Park populations. Essentially no reduction or degradation due to threats, outside the park, wetland degradation and draining would be significant threats.