254 



COLLEGE ZOOLOGY 



castes: (1) sexuals (kings and queens), (2) 

 workers, and (3) soldiers. The first type, the 

 reproductive individuals, may possess func- 

 tional wings, small nonfunctional wings, or 

 no wings. The winged kings (males) and 

 queens (females) leave the colony, mate, 

 lose their wings at a particular breaking 

 point, and start a new colony. 



The second caste consists of the male and 

 female workers, and the third caste of male 

 and female soldiers. They have no wings and 

 no functional sex organs. The workers are 

 more numerous than any other caste. They 

 care for the eggs and young, feed and tend 

 the queen, obtain food, cultivate fungus in 

 special chambers in certain species, excavate 

 tunnels and galleries, construct mounds, and 

 perform other duties. 



The soldiers are the most highly special- 

 ized. Two castes may be present: one has a 

 large body, strong head, and huge mandi- 



bles for driving away intruders; the other 

 carries on chemical warfare by means of a 

 pore in the head through which a repellent 

 fluid may be ejected. That the soldiers are 

 not very successful is indicated by the fact 

 that over 100 species of other insects, ara- 

 chnids, centipedes, and millipedes live regu- 

 larly as guests in the nests of termites. 



RELATIONS OF 

 INSECTS TO MAN 



Beneficial insects 



Insects of importance to human welfare 

 have been mentioned in the preceding 

 pages. Some of them are beneficial, but more 

 are injurious. Among the beneficial insects 

 are those that produce honey, wax, silk, lac, 

 and cochineal; those that cross-fertilize (pol- 



'f-vi.V';-:f:MiT.t 



Cocoon 



containing 



pupa 



Adult female 



Egg 



Figure 153. A beneficial insect, the silkworm. 



lenize) flowers; and those that destroy in- 

 jurous insects either by devouring or para- 

 sitizing them. Injurious insects include farm 

 and household pests, and species that trans- 

 mit disease agents. 

 The honey bee (Fig. 150) produces about 



250,000,000 pounds of honey in the United 

 States every year. We also use about 10 

 million pounds of beeswax annually. Silk- 

 worms (Fig. 153) spin about 1000 feet of 

 thread to make each cocoon, and about 

 25,000 cocoons are necessary to manufacture 



