Giant Golden Stonefly nymphs are common in rivers and streams of the west. This particular one was found in Rock Creek near Clinton, Montana. They live among cobbles and boulders, capturing other aquatic insects to eat — especially midges, blackflies and small mayflies. After a series of molts and successfully avoiding the attention of hungry fish, they crawl out of the water and then molt one last time to emerge as adults. If you look carefully at the water’s edge you may find one of these “two-tailed” exoskeletons clinging to a rock, plant, or other object.
Adults are around 1 and a half inches long (with wings), weak fliers and are seldom found far from where they developed. They fly by day and are fairly short lived, rarely lasting more than a couple weeks and often living only for a few days. (Many species in the Perlidae family, called the Common Stoneflies, develop from egg to adult in a year, but large species may take up to four year to complete development.)
Photo by Heather McKee around 10/4/20 near Clinton, MT