398 APPLIED BIOLOGY 



which infest rats in whose blood the germs occur. In fact, 

 any biting insect which gets an opportunity to bite any 

 person or animal whose blood contains disease germs may 

 become a carrier of the germs ; and any insect which comes 

 in contact with germs and later with human food may in- 

 directly cause disease. 



The above account suggests the general relations of 

 certain insects to human diseases. For more facts on this 

 very important subject read the pamphlets on " Mosquitoes " 

 and " Insects and Health " published by the United States 

 Department of Agriculture. 



332. Adaptations of Insects. No other group of animals 

 is so favorable as the insects for study of adaptations of 

 structures to special uses. 



Insect legs are adapted to running (cockroach), leaping 

 (grasshopper), walking (fly), grasping (mantis), burrowing 

 (mole-cricket), clinging (moths and butterflies), carrying 

 pollen (bees), and to still other special uses. However, in 

 all these cases the general plan of a leg is similar. 



The mouth-parts are adapted to various kinds of foods; 

 biting and chewing (grasshopper, beetles), piercing (mos- 

 quito, hemipterans, and some flies), licking (house-fly), 

 sucking (butterflies), and cutting (carpenter-bee). 



The wings are commonly well adapted to flying, but in 

 some species (e.g., fleas) wings would be worse than useless 

 organs and have become degenerate. The front wings of 

 beetles are thickened to -form shield-like covers for the pos- 

 terior wings. In protective "adaptation of some insects the 

 wings are remarkably leaf -like in appearance. 



The form of insect bodies is strikingly modified in many 

 species. Stick-insects (Phasmidse) are orthopterans in 

 which the body and legs are stick-like and easily mistaken 

 for sticks, twigs, straws, etc., near which these insects live. 



Some of the most remarkable adaptations are connected 

 with the larval stages. Larvae of May-flies and others 



