272 A BOOK OF INSECTS 



As might be expected, the parental instincts of insects 

 are most strongly marked among the social groups. In- 

 deed, in the case of the Hymenoptera, at least, we shall 

 see that they constitute the foundation upon which the 

 whole superstructure of insect communism is based ; for 

 a bee-hive or an ants' nest is neither more nor less than 

 a vast co-operative nursing establishment. The extra- 

 ordinary caste system has been evolved in order that a 

 few individuals may devote their energies exclusively to 

 procreation, while a vast army of helpers is at hand to 

 care for the enormous and ever-growing family. With 

 these matters we shall deal more fully in the next chapter. 



Among insects in general the male is exempt from 

 family cares ; but there are several interesting exceptions. 

 Certain bark-beetles {Scolytidce) are polygamous, and in 

 these species the male exerts himself to form a circular 

 excavation beneath the bark, wherein he receives the 

 members of his harem. The females, however, construct 

 their respective brood-galleries, which radiate from the 

 nuptial chamber. We have already seen that sexton 

 beetles (Necrophorus) of both sexes labour in company 

 to bury the carcass in which the eggs are to be laid. 

 A similar co-operation seems to occur among some of the 

 scavenger beetles, although in other species, according to 

 Fabre, the female receives no assistance from her mate. 

 Among the large water-bugs of the genus Zaitha, the 

 eggs are carried on the back of the adult insect, and until 

 recently the female was assumed to be the bearer. But 

 observations made by an American lady, Miss Slater, 

 have established the remarkable fact that the female 

 actually captures a male and deliberately glues her eggs 

 to his back. " That the male chafes under the burden is 

 unmistakable ; in fact my suspicions as to the sex of the 

 egg- carrier were first aroused by watching one in an 



