AQUATIC INSECTS IN THE ADIRONDACKS 4I3 



The nymphs of stone flies require well aerated water. They can not 

 live in a stagnant pool^, or in a foul stream. A large number of the 

 smaller species, including the two described below, are entirely destitute 

 of gills. With these the air supply is absorbed directly through the thin 

 skin of the ventral surface. At the ventral sutures one can readily see 

 that the skin is fully permeated by fine tracheal branches. Stone fly gills 

 at their best development are but small tufts of delicate respiratory fila- 

 ments attached to the ventral surface of the body, oftenest about the 

 bases of the legs, swished about by the motion of other parts, or depend- 

 ent on the motion of the water for the renewal of the oxygen supply. 

 Nymphs brought in from the brook and placed in a vessel of still water 

 will soon be seen with claws affixed vigorously swinging the body up and 

 down, trying to get a breath under the difficult conditions into which tuey 

 have been brought. 



In two important respects the nymphs of May flies and dragon flies 

 have surpassed those of stone flies in the development of aquatic respira- 

 tory apparatus : 



1 In developing flat, plate like gills, which offer greater surface for 

 contact with the water ; 



2 In developing special apparatus for the independent movement of the 

 gills, or for causing currents of water to flow over them. 



It is the smaller species that are gill-less. The extent of respiratory 

 surface is in a measure proportioned, i) to the size of the nymphs; 2) to 

 the condition of the water, whether well or poorly aerated. 



It is because of the limitations on the respiratory system of stone-fly 

 nymphs that they are so restricted in their aquatic habitat. 



As to the food of the stone flies there have been a number of guesses, 

 but apparently no careful and continuous observations recorded. It is 

 supposed that the nymphs of the larger species eat smaller May fly 

 nymphs, and soft-bodied dipterous larvae associated with them on the 

 rocks; but Benjamin D. Walsh has said that perlid nymphs eat decaying 

 vegetable matter, and that the images eat nothing.2 Here, then, is an 

 opportunity for some careful observer to replace inferences with facts. 



The adult stone flies may be collected at almost any season of the 

 year. The little black capnias emerge in winter. They live mainly in 

 small brooks, and are often found in transformation on the edge of the 

 ice. Through the -spring months the dusky and grayish little nemouras 



1 1 have bred a species of Acroneurla In some numbers from nymphs taken from rotting oak 

 leaves in the edge of an ice pond at Ithaca N. Y.; but the water about the bed of leaves was clear, 

 and could not be called stagnant, since the turbulent CascadlUa creek flows through the pond. 



2 Practical entomologist. 2:73. 



