Economic Importance of Animals 571 



on different kinds of plants are produced by specific kinds of insects. 

 The crane flies resemble large mosquitoes, and the midges resemble small 

 mosquitoes, for which they are both commonly mistaken. 



Order 21 — Siphonaptera: Fleas live among the feathers of birds and 

 the hair of wild or domestic mammals. The human flea and the chigoe 

 are important enemies of man. The latter burrows in the skin and is 

 not the common chigger which is a mite belonging to the class Arach- 

 noidea. The dog and cat flea is quite common and attacks dogs, cats, 

 and human beings (Fig. 304). They most frequently breed in the dirt 

 and filth, although they have recently been encountered in large quan- 

 tities in the grass and weeds out of doors. The rat flea transmits the 

 bacterium which causes bubonic plague from rats and ground squirrels 

 to man. The larvae of fleas feed on decaying plant and animal matter 

 so these should be destroyed in our attempt to eliminate the adult fleas. 



s?fe 



adult male 



pupa 



Fig. 305. — Development of the black ant (Monomorium sp.) of the order Hymen- 

 opt era. (Copyright by General Biological Supply House, Inc., Chicago.) 



Order 22 — Hymenopetra: Honeybees (Figs. 195 to 200) collect 

 nectar from flowers which is changed chemically, dehydrated, and made 

 into honey which is sealed in the wax "cells" of the honeycomb. Honey- 

 bees also pollinate certain types of .flowers which they visit. Beeswax 

 is secreted by glands on the underside of the abdomen. Bees have been 

 studied extensively as representatives of social life among the animals. 

 The so-called mud-daubing wasps construct nests of mud and catch 

 other insects which are placed in these nests for food for the young 

 wasps after they hatch. Other species of wasps excavate tunnels in the 

 earth or dig cavities in wood. Yellow jackets build nests consisting of 

 a series of combs surrounded by a paperlike covering. Bumblebees live 

 in colonies in the summer and assist in pollination of clovers for seed 

 production. Ants (Fig. 305) are colonial insects whose social life has 

 been studied extensively. A colony, as in the case of social bees and 

 wasps, contains different types of individuals (workers, males, female 



