Big Golden Stones

Every angler who turns over a rock now and then is familiar with the flat bodied and hastily scurrying examples of the family Perlidae. It contains most of the large stonefly species common to freestone streams across the continent. There are fifteen genera of this large and abundant family currently recognized in North America. They are easy to tell from Pteronarcyidae species (Eastern Giant Black Stonefly, Salmonfly) by their lighter, patterned coloration. Their longer tails and large triangular heads are also easy to spot differences. The males are substantially smaller than the females.

Perlidae species are very similar in conformation and habits. With some exceptions, telling them apart is very difficult East of the Rockies where ten of the genera reside and more than 50 species are involved. They have a number of common names: Stonefly Creeper, Yellow Legged Stonefly, American Brown Stone, to name a few.

The nymphs range in coloration from dark brown, delicately patterned gold and amber, to a brilliant yellow and black striped pattern reminiscent of Bengal tigers. The latter description befits them in recognition of their predator status. Their rarely abundant populations and nocturnal habits make them limited in importance back East, but out West, the story is quite different.

In the Rocky Mountain and Pacific Coast States, perlids exist in tremendous numbers and perhaps more importantly, they are very active during daylight hours. Ironically, in spite of the large populations the entire family is represented by only five species and most of the activity involves only two, Calineuria californica and Hesperoperla pacifica. The entomologically astute angler can easily tell these western species apart in the hand by comparing head markings and gill location of the nymphs. The adults are easily sorted as well by knowing the different hammer (Hammer: A smooth clearly defined chitinous area on the ventral surface of the ninth abdominal segment of some male stoneflies used for drumming up mates.) shapes of the males and dorsal (Dorsal: Top.) markings of both sexes.

Anglers need to take note that taxonomic revisions have moved four of the five western species formerly classified under Acroneuria to new genera, though like the two already mentioned, they are easily recognized in the taxa lists by their retained species names. All remaining Acroneuria species are now east of the Rockies.