Great Basin Naturalist


During an investigation of some of the stoneflies (Plecoptera) of Mill Creek, Wasatch Mountains, Utah, Megarcys signata, a large omnivorous stonefly, was found to have a univoltine life history and a slow seasonal life cycle.

Temperature appears to affect the growth rate of Megarcys signata. Warmer stream temperatures accompany the acceleration of the growth rate, whereas cooler stream temperatures apparently retard the growth rate.

Periods of maximum absolute growth rate correspond with maximum carnivorous feeding from August to September and March to April. Chironomidae, Ephemeroptera, and Plecoptera, in that order, were the most abundant prey in the foreguts. Young nymphs ingested considerable amounts of diatoms, filamentous algae, and detritus but not as much animal matter as did older nymphs.

Megarcys signata was uniformly distributed throughout Mill Creek, except at the lowest station, where few nymphs were found.

Emergence occurred in May and June, the peak occurring in June. The mean size of females and males decreased as emergence progressed.