THE CLASSIFICATION OF INSECTS 



169 



occur in North America. None of them is injurious. The 

 larvae of many species are eaten by fish. 



Order Coleoptera. The great order of Coleoptera, or bee- 

 tles, is the largest of all the insect groups, and many of its 

 members are among the most familiar of our insect friends and 

 enemies. More than 12,000 species are known in North 

 America north of Mexico. They represent nearly 2000 genera 

 grouped into 80 families. The classification of the Coleoptera 

 is one of the most difficult subjects in the 

 study of systematic entomology, and but 

 few entomologists know more than a few 

 score or few hundred of the commoner 

 kinds. The beetles are mostly readily dis- 

 tinguished by their horny fore wings, or 

 elytra, which serve as protecting covers for 



FIG. 79. Water- 

 tiger, the larva of the 

 predaceous water-bee- 

 tle, Dyttcus sp. (Nat- 

 ural size.) 



FIG. 80. The predaceous water-beetle, Dy- 

 ticus sp. pupa and adult. (Natural size.) 



the large membranous hind wings. They all have strong bit- 

 ing mouth-parts and a firm dark chitinized cuticle or outer 

 body-wall. The body is usually short and robust with its 

 segments well fused together. There is much variety in the 

 character of the antennas and feet, and these differences are 

 largely relied on in classifying beetles into different families. 

 The eggs are laid underground, or on leaves or twigs or in 

 branches or trunks of live trees, in fallen logs or in decaying 



