THE SOCIAL INSECTS 



A number of beetles, for instance, have tufts of yellow hairs 

 which produce some aromatic substance to which ants are 

 strongly attracted. The ants lick the hairs and take as much 

 care of the beetles as they do of their own brood. Yet often 

 the beetles feed on the ant-grubs and are dangerous parasites 

 of the colony. The caterpillars of some of the blue butterflies 

 have a gland which produces a sweet secretion which ants 

 eagerly lick up. Some of the caterpillars are carried into the 

 nest by the ants and carefully tended. And yet the food of 

 the caterpillars is either the aphid ant-cows, or else the brood 

 of the ants themselves. Other insects, like the flies observed 

 by Farquharson in Africa, while not parasites of the colony, 

 have evolved a way of soliciting a meal from the foraging 

 workers so that they can obtain a share of the food intended 

 for the grubs. 



SOCIAL PARASITES 



All these insects are parasites of social insects, but are not 

 themselves social. But there is another group of parasites 

 whose behaviour is more like that of the cuckoo who lays 

 her eggs in the nests of other birds. These are the real social 

 parasites : species of wasps, bees and ants, mostly without 

 a worker caste of their own, which lay their eggs in the nest 

 of some other species of their own group. This behaviour 

 is evidently not so much a response to the direct struggle for 

 food and shelter as to the difficulties and dangers of founding 

 a new colony. Amongst the social wasps certain species both 

 of Vespula and of Polistes have become social parasites of this 

 type. The cuckoo Vespula, of which there are three in 

 western Europe and one, V. austriaca, in England, can be 

 recognised in the queen by slight differences in the shape of 

 various parts of the head. The differences are not very pro- 

 nounced, but have been supposed to be advantageous in 



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