THOMAS SAY FOUNDATION 



BIOLOGY. 



Stoneflies in their immature stage are all inhabitants 

 of running water, and so are to be sought as adults in 

 the vicinity of streams. There is hardly a better way of 

 obtaining the smaller and less active species than the old- 

 fashioned entomologists' method of beating the bushes 

 over an inverted umbrella, or sweeping the streamside 

 vegetation with a heavy beating net. Many of the larger 

 Perlidae are attracted to lights at night and may be 

 sought about the street lamps near streams. The senior 

 author once found the stout-bodied stonefiy Acroneuria pa- 

 ct ilea, clinging in numbers to young pine trees on the steep 

 slopes of the Yellowstone Canyon, and obtained specimens 

 very easily by shaking the trees, dashing the stoneflies to 

 the ground, and picking them up before they had run to 

 cover. 



Only a few forms, mostly the greenish ones, are active 

 by day, and run about over foliage. For the most part 

 they do not take flight quickly, but many of them run 

 rapidly and slip into hiding places most adroitly. Adult 

 stoneflies may be collected even in northern latitudes 

 every month in the year. The small black Capniidae are 

 the winter forms. These are usually seen on warm days 

 in winter on fresh banks of snow, where their color makes 

 them conspicuous. A number of dusky-winged Nemou- 

 ridae next follow in early spring. The big Pteronarcidae 

 come next, and the Perlidae fill out the season. Most 

 characteristic of midsummer are the greenish, diurnal 

 foliage-inhabiting stoneflies of the genera Isoperla, Al- 

 loperla, and Chloroperla. 



The immature stage (larva, nymph or naiad) re- 

 sembles, in general, the adult, but the wings are lacking 

 and they always occur in water, either under stones or 

 under drifted leaves, debris, etc. The mouthparts are of 

 the biting type and are well developed. As far as we 

 know, all nymphs possess long filamentous, many-seg- 

 mented cerci. Tracheal gills are present in most genera 

 and are mostly of the filamentous type. The gills may 

 occur in tufts, or as single filaments and are placed on the 

 sides of the thorax, on the sides and tip of the abdomen 

 or in the cervical region. In Taeniopteryx they consist 

 of three-segmented filaments attached to the coxae. The 

 gills persist in some of the adults, but are non-functional. 



Comparatively little work has been done on the biology 

 of stoneflies. At least one year seems to be required 



