THE ANTS OR PISMIRES 



alien workers bring up the early broods of the intruding 

 queen, and as they die off and are not replaced the colony 

 gradually becomes a society of the intruding species only. 

 This type of behaviour seems to lead in the end to more and 

 more pronounced parasitism of the sort which will be 

 described in the next chapter. A well-known example of a 

 temporary social parasite is the British wood ant, Formica 

 rufa, which may found colonies by budding but whose 

 queens also invade the nests of another ant, Formica fusca. 



An entirely different method of solving this problem has 

 been evolved amongst the driver, legionary and a few other 

 kinds of ants. In them, the ant which lays all the eggs is 

 wingless, blind and has a thorax formed like a worker rather 

 than a queen. It is supposed that in these species the original 

 queen has entirely dropped out, and that her functions have 

 been taken over by a special type of egg-laying worker. 

 Since this acting queen has no wings she mates on the ground 

 and the species spreads only by the wanderings of the whole 

 colony. This arrangement is not found in many kinds of 

 ants, and probably has the same disadvantages as ordinary 

 budding, especially a loss of mobility for the species. 



THE CASTES OF ANTS 



As a rule, in any one species the male and female are rather 

 constant in form and colour, while the workers are much 

 more variable. In the common, yellow, mound-making ant, 

 the workers vary in size only to a moderate extent. In the 

 wood ant the variation in size is much greater, and there is 

 also a good range in the amount of black markings. 



In many non-British ants the variation or polymorphism 

 is much more marked. In driver ants or leaf-cutting ants the 

 biggest workers are many times the size of the smallest ones. 

 Moreover the shape of the mandibles, or of spines on the 



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