THE SOCIAL INSECTS 



of the argument is that the efficiency of this type of organi- 

 sation, measured by its rate of reproduction, increases 

 rapidly with time. In general, short-lived colonies are less 

 efficient than ones which last longer. Thus the winter rest 

 which is imposed by the temperate climates raises a very real 

 difficulty. It seems likely that this has been overcome in a 

 few species which have managed to evolve special modifica- 

 tions. The relatively large size of the queen in Vespula may 

 be one of these ; so also is their ability to lay up a large store 

 of internal fat which keeps them alive during hibernation. 



The probability that social wasps first arose in the tropics 

 is one reason why it is interesting to examine the Polybia 

 wasps, the largest tropical group of social species. Most of 

 them are found in Central and South America, but a few 

 also in tropical Africa and Asia. One or two penetrate a little 

 way into the United States. In 1937, my wife and I made a 

 special study of them in British Guiana, and much of what is 

 written below is based on personal observations. The general 

 picture of their biology was already known, especially from 

 the work of the von Iherings and of Ducke, but there were a 

 great many gaps to fill in matters of detail. 



With few exceptions these wasps found their colonies by 

 swarming. The swarms seem to consist of young fertilised 

 queens accompanied by a large group of workers. Since 

 males are never found in young nests, it is probable that they 

 die after fertilising the queens. Usually several egg-laying 

 queens are found in each nest ; the number varies a good 

 deal even in a single species and some colonies may have only 

 one queen. More often there are four to ten, and in some 

 species a hundred or more. It is hardly ever possible to tell 

 the workers from the queens at sight without dissecting them 

 to examine the ovaries. In some species, however, the 

 abdomen of the older queens becomes swollen after egg- 



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