THE SOCIAL INSECTS 



when they breed in the spring. This illustrates a difficulty 

 in adjusting reproduction to social life more fundamental 

 than the mere avoidance of over-eating the food supply. 

 Sexual reproduction tends to have a disruptive effect on social 

 organisation. In solitary bees and wasps one can often see 

 the nest-building females being pestered by ardent males 

 which still attempt to pair though the busy females no longer 

 need their attentions. Man is almost the only social animal 

 in which nearly all the adults of the right age are capable of 

 breeding at any season of the year. Probably all the other 

 social vertebrates, such as deer or beavers, have a relatively 

 short breeding season, outside which the relations of the 

 sexes are platonic. The majority of birds and mammals also 

 have some sort of territorial system. The male robin, for 

 example, at the beginning of the nesting season, occupies a 

 territory out of which other males are driven. His song 

 advertises his presence to unpaired females and also warns off 

 other members of the species. In this way he claims an area 

 of about the right size to supply one pair and their young 

 with food. In most seasons, some of the males fail to obtain 

 a territory and do not breed. Social insects, though they may, 

 as in ants, only forage in a limited area, defend the territory 

 only in the immediate neighbourhood of the nest. 



The problem of too rapid multiplication in the social 

 insects has been met in a different way. One of the first steps 

 in the evolution of their social life was to establish a sterile 

 caste which either did not breed at all or did so only to a 

 limited extent and under certain conditions. They established 

 a distinction between egg-laying to produce workers and 

 egg-laying to produce sexual forms ; only the second process 

 needs severe regulation. In the less advanced societies, such 

 as those of the common wasps, the production of sexual forms 

 leads to the break up of the colony. This does not seem to be 



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