AQUATIC INSECTS OF FRESHWATER 



and waterways. These attack, all winged insects, none seem too large to 

 escape their onslaughts; but their principal prey is the evening flying 

 Diptera and juicy, winged insects. The "Swift-flying dragon-flies" com- 

 prise the genera iEschnina, Gomphus, Anax, Cordulia, Tramea, Libellula, 

 Celithemis and Diplax; some of them nearly as swift of wing as ^schna 

 but not capable of as lofty and long-sustained flight. Dragon-flies are 

 local in their habits, rarely flying far from their accustomed haunts, except 

 in occasional cases of migration. Belostoma, Notonecta, Ranatra and 

 other predaceous insects prey on the younger Dragon-fly larvas, and frogs 

 will take the perfect insect, as will also some of the birds, notably the Fly- 

 catchers. It may be noted that Dragon-flies are most inveterate enemies 

 of the mosquito in all the stages of its development, attempts having been 

 made to introduce them extensively to aid in exterminating this pest. 

 The most common species of Dragon-flies in the Eastern and Middle 

 States are Gomphus exilis, Cordulegaster maculatus, Mschna heros, A. 

 clepsydra, Anax Junius, Tramea Carolina, Libellula pulchella, Celithemis 

 elisa, Diplax ribicunda, Calopteryx maculata, Lesles unguiculata, Epicordulia 

 princeps and Argia violacea. Fig. 216. Agrion is not found in the 

 Eastern section of the United States. 



Caddice-Flies or Caddice-Worms belong to the order of Trichop- 

 tera, signifying hair-winged. They are mothlike insects usually having 

 four membranous wings with numerous longitudinal veins, few cross veins 

 and more or less clothed with hairs, which, at rest, are folded against 

 the abdomen, the hind wings being usually the broader. They are com- 

 mon near ponds, streams and lakes and frequent shady places, resting on 

 leaves and twigs, rarely flying during the day. The eggs are laid in gela- 

 tinous masses attached to water plants. The larvae, known as Rock-worms, 

 are aquatic, elongate and cylindrical in form with a tough horny head and 

 thorax and a soft thin-skinned abdomen; which construct protective cases, 

 open at the ends, of any available materials, leaves, twigs, sand, shells and 

 small stones, all spun together by means of silk threads, to protect the 

 Caddice-worm from predatory insects and other natural enemies. They 

 breathe by tracheal gills at the side of the abdomen, and live several 

 months in the larval condition, passing the pupal stage in the cases, both 

 ends of which are then sealed with a silk netting. The final metamor- 

 phosis takes place above the water on plants or on the banks, the fly 

 emerging from the pupa fully developed and immediately takes to flight. 

 The food of the larvae is principally vegetal, but one family is carnivorous 

 and feeds upon small insect larvae. There are more than 150 North 

 American species, the more generally distributed of the Eastern and 

 Middle States being Phryganea interrupta. Fig. 213, Limnephilus rhombicus, 



263 



