THE SOCIAL INSECTS 



than are the cuckoo Vespula. It is not even certain whether 

 one of them may not produce a few workers, for in this group 

 it is difficult to separate queens from workers unless the 

 wasps are dissected. 



The way in which the cuckoo queen establishes herself is 

 not known, but it seems that the host queen is somehow 

 eliminated, perhaps after a fight. The brood which is later 

 produced consists mainly of males and females of the cuckoo 

 species, with a few workers and males but no queens of the 

 host. Even the later host workers hatch only from cells 

 occupied before the cuckoo queen takes over. It seems 

 significant that in both these kinds of cuckoo wasp it is the 

 young queens of the host brood that are particularly elimin- 

 ated. This is not to the advantage of the parasite, since it 

 means that there will be fewer nests to invade in the following 

 year. It suggests rather that queens are, so to speak, " expen- 

 sive " for the colony to produce. It would then be difficult 

 either from the point of view of labour or of the supply of 

 some scarce food to produce queens of two kinds. 



The cuckoo humble bees of the queens Psithyrus are more 

 different from their hosts than are the cuckoo wasps. The 

 name of these bees means "whisperer", because the female in 

 flying makes a much less pronounced hum than does a true 

 Bombus ; but the most striking difference in this sex is the 

 loss of the pollen-collecting apparatus. There is no pollen- 

 basket on the hind leg and instead of a shining, rather con- 

 cave surface there is a convex, densely hairy one. The sting 

 is more powerful, and the whole skeleton is stronger and 

 more thoroughly articulated against attack. The worker 

 caste is absent. 



As in the ordinary humble bees, males and females are 

 produced in the autumn, and after fertilisation the females 

 hibernate in a shallow hole in a bank. When they come out 



i54 



