BUGS WITH OVERLAPPING WINGS 



41 



than six million dollars' worth of grain in only thirteen 

 counties in Illinois (see Fig. 62). 



Water Bugs. In almost every pond and stream, not only 

 in the United States but almost anywhere on the earth, are 

 to be found oval gray and black insects, usually a little 

 over a centimeter long (about half an inch). These are 

 water boatmen (Corix'a, Fig. 25, B). They have a long beak. 

 With this they suck the 

 body fluids of other water 

 creatures. They are adapted 

 to rapid locomotion in the 

 water by means of the length- 

 ened and fringed middle and 

 hind legs. They breathe a 

 thin film of air, which is 

 caught in the fine hairs which 

 cover the body, making them 

 look as if incased in polished 

 metal. Slight movements of 

 the legs cause currents of 

 water to pass over this air 

 film, helping to purify it, 



Fig. 25. Water bugs. (All slightly 

 enlarged) 



and making frequent Visits ^back swimmer, ventral view; A' back 

 & ^ swimmer, dorsal view; B, water boatman 



to the surface unnecessary. 



When the boatman is at the surface, air is taken into a 

 cavity under the wings, where the spiracles are placed, so 

 that quite a supply is on hand at all times. While these 

 insects are thus adapted to water life, at the same time 

 they can fly ; and they often leave their native element, espe- 

 cially if it is in danger of becoming dry. 



Another widely distributed group of insects resembling 

 the foregoing are the back swimmers (Notonec'ta, Fig. 25, A, 

 A'), which have the curious habit of swimming on their 

 backs, as their common and scientific names denote. A favor- 



