
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. 
Orver 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 Coriside; the Backswimmers 
or Notonectide; the Water-scorpions or Nepidz; the Giant Water-bugs 
or Belostomide; and the Creeping Water-bugs or Naucoride. Those 
which live near the water and are semi-aquatic are the Toad-bugs or Gal- 
gulide; the Broad-shouldered Water-striders or Valiide; the Water- 
striders or Hydrobatide; and the Marsh-treaders or Limnobatide: all of 
which will be described in this order. 
Warer-Boatmen belong to the family of Coriside 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 3¢ inch long, eyes small and inconspicuous, ie 
and the body covered with fine hairs, which, in 
the water, cause an almost complete envelopment 
in air like a glittering armor, and enables the 
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-like, covered with swimming bristles. RIG! 166) Wien 
The four membranous wings lie on the back, the Corisa interupta. 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 
