AQUATIC INSECTS 903 



psychidae crawl beneath the water and spread their eggs in a 

 single layer over the lee side of stones in the gentler currents. 

 The big forms of Phryganea fasten their pretty green eggs in 

 a gelatinous ring (Fig. 1373) on the stem of some aquatic plant. 



AQUATIC MOTHS (Order Lepidoptera) 



Of this great order of insects, only a few moths of the family 

 Pyralidae are aquatic. Many moths live as larvae on plants by the 

 waterside, and a few burrow in the tissues of submerged aquatic 

 plants, obtaining their air from the airspaces of the plant stems. 

 The aquatic caterpillars, like their terrestrial relatives, are distin- 

 guished from larvae of other orders by the possession of a brown 

 chitinous shield covering the prothoracic segment, by bristle-bear- 

 ing tubercles regularly disposed over the body and by fleshy grasp- 

 ing prolegs beneath the abdomen. 



There are three types of aquatic larvae found commonly in our 

 fresh waters, two in ponds and one in rapid streams. 



The larvae of Nymphula (Hydrocampa) are destitute of gills, and 

 greatly resemble pale terrestrial caterpillars. They live in flat 

 cases composed of two pieces cut out from green leaves of river- 

 weed or water-lily, and fastened together and lined with silk. 

 They live near the surface of the water. During the pupal stage 

 the cases are often found floating. The eggs are laid on or under 

 floating leaves. 



The larvae of Paraponyx are provided with abundant branching 

 gills, which surround the body like a white fringe. These larvae live 

 in similar cases or between leaves in sheltering crevices that are 

 lined with silk. 



The larvae of Elophila fulicalis, as recently described by Lloyd 

 from Ithaca, N. Y., live on the stones in rapid streams, protected 

 by an irregular shelter of thin-spun silk. They are in form strongly 

 depressed, and have unbranched gills arranged in two longitudinal 

 lateral rows. They feed mainly on such green algae as grow near 

 at hand. Each larva when grown fashions a broadly dome-shaped 

 pupal shelter or half-cocoon under some portion of the larval 

 shelter, with a row of marginal openings at either side to permit 

 free circulation of water and air through it. 



