THE SOCIAL INSECTS 



proportion is lower in tropical regions, and it is possible 

 that the difficulties of colony foundation in a temperate 

 climate have favoured the development of such parasites. 



It is a curious point that slavery and parasitism of this type 

 do not seem to occur in the termites. A few cases of com- 

 pound nests, rather like those of Formicoxenus and Formica, 

 are the nearest approach to it. It is not clear why termites 

 have not shown this type of evolution. It may be partly 

 because in them the queen is always attended by a male and 

 mating has often to be repeated. The invasion of a strange 

 nest by the two sexes together might be more difficult. 

 Another possibility is that it would be harder to eliminate the 

 reproduction of the host species, since when the original 

 queen is killed alternative queens can readily be produced. 

 A similar argument might be applied to the honey bee and 

 its allies, since these are not subject to attacks by cuckoo 

 species. Such suggestions, however, are at the best very 

 tentative, and there is still much in the evolution of the 

 parasites which we do not understand. 



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