AQUATIC INSECTS OF FRESHWATER 



though there is often more than one summer brood, and many remain 

 more than a year in the larval state. A further provision of nature is the 

 enormous number of eggs produced. 



No insect is so completely aquatic as to pass its entire existence in 

 the water, yet the final perfect stage and the acquisition of wings is usually 

 a brief one; its purpose being principally the mating of the sexes and the 

 distribution of the eggs over a wider area, where the chances of survival 

 are improved. Fig. 195 shows the external anatomy of a beetle. 



Insect Enemies. The following are the principal insect enemies of 

 the freshwater fishes. 



Order Hemiptera. This order includes three sub-orders, the 

 Heteroptera, Parasitica and Homoptera; the aquatic and semi-aquatic 

 bugs belonging to the first named. They have four membranous wings, 

 the first pair partly overlapping the others. The mouth parts are devel- 

 oped for piercing and sucking. Many families are comprised in this 

 sub-order including the Water-boatmen or Corisidae; the Backswimmers 

 or Notonectidae; the Water-scorpions or Nepidae; the Giant Water-bugs 

 or Belostomidas; and the Creeping Water-bugs or Naucoridas. Those 

 which live near the water and are semi-aquatic are the Toad-bugs or Gal- 

 gulidae; the Broad-shouldered Water-striders or Valiidae; the Water- 

 striders or Hydrobatidae; and the Marsh-treaders or Limnobatidae: all of 

 which will be described in this order. 



Water-Boatmen belong to the family of Corisidae and about 

 forty North American species to the genus Corisa. They are of oval 

 form, flattened on the back and below, of mottled grey and black color, 

 about 34 inch long, eyes small and inconspicuous, 

 and the body covered with fine hairs, which, in 

 the water, cause an almost complete envelopment /j^^ I 

 in air like a glittering armor, and enables the /^ ^t 

 bug to descend below the surface for considerable ' ^ ^ 

 periods, where it attaches itself by its anterior 

 legs. The posterior legs are more largely devel- 

 oped and oar-Hke, covered with swimming bristles. „,^ , „ 



__, r I . ^"' '9°' Water-boatman, 



1 he rour membranous wmgs lie on the back, the (^'"''"' '"'enpta. Enlarged.* 

 first pair of thicker structure, the hind wings very delicate, white and lace- 

 like. It swims with the back upwards and in cold weather buries itself in 

 the mud and lies dormant until spring. The eggs are attached to the stems 

 of plants under the water and the larval stage is brief. All the genera are 

 predatory, the food consisting of insects and other aquatic animals, and the 

 strong and sharp beak inflicting severe bites. They are destructive to 



*The line at the right of the figures indicate the natural size. 



252 



