SOCIAL PARASITES 



the workers ; these will later feed her and tend her brood. 

 The workers which she has taken over are afterwards 

 replaced by new slaves obtained by the raids of amazon 

 workers, so that the colony never becomes pure for one 

 species as in a temporary social parasite. 



PARASITISM AND DEGENERATION 



There are a great many more kinds of parasitic ants, and 

 they all have sickle-shaped mandibles and are in various 

 degrees incapable of maintaining the colony unaided. A few 

 seem to be slave-keepers rather after the pattern of the 

 amazons, with pugnacious workers. But many are more 

 degenerate and occupy a relatively subordinate position in 

 the host colony both as regards numbers and behaviour. 

 They have, in fact, become much more like true parasites, 

 and their chief effect in this case is to prevent normal repro- 

 duction by the host species. All the more degenerate 

 parasitic ants have lost the worker caste. Many of them 

 are found in only a few localities and are rarely seen. It 

 appears that such behaviour is not ultimately a reliable way 

 of perpetuating the species. Moreover, once a species has 

 reached the stage realised in the amazons, there is no 

 return. 



In Great Britain there are three species of ant which are 

 permanent social parasites and which, though not closely 

 related to one another, are examples of three stages in degen- 

 eration. Formicoxenus nitidulus lives exclusively in the nests 

 of the very much larger wood ant, Formica rufa, and some 

 other very similar species. It excayates small chambers in the 

 recesses of the nest and looks after its own brood. Owing to 

 its small size the galleries it uses are inaccessible to the workers 

 of its much larger host, but it is able to wander freely through- 

 out the Formica nest. Its natural food is unknown, but it will 



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