246 THE BIOLOGY OF INSECTS 



workers that share in the labours of the captors. According 

 to Wheeler's observ^ation a young scmguinea queen is in- 

 capable of establishing a nest of her own ; she therefore 

 enters a fusca nest, and seizes a number of worker-pupae, 

 killing any fusca workers that seek to interfere with her. 

 The gang of workers she has annexed begin as soon as they 

 have emerged to feed her and tend the grubs hatched from 

 her eggs. The sanguinea workers reared from these have 

 the inherited instinct to raid nests of fusca and capture 

 larvae and pupae ; thus a mixed community is formed, the 

 workers of the two species sharing in the common labour. 



Communities of Formica fusca suffer also from raids by 

 '' Amazon Ants " (Polyergus), oppressors more formidable 

 than F. sanguinea. There are several species of Polyergus, 

 most of them, like the well-known P. rufescens, bright red 

 in colour, provided with sharp, slender curved mandibles 

 " perfectly adapted for fighting but of no use for digging 

 in the earth or capturing food." The main facts about the 

 behaviour of these slave-making ants were described more 

 than a century ago by P. Huber (1810), who bestowed on 

 them the suggestive title of '' Amazon." Extensive observa- 

 tions on the European forms were subsequently made by 

 Forel (1874), while C. Emery (191 1) has given an account 

 of the foundation of a community by the young queen 

 Polyergus. She invades a weak nest of Formica fusca, kills 

 its queen by biting into her head, and then is adopted by 

 the fusca workers, which tend and feed the grubs hatched 

 from the amazon's eggs. The Polyergus workers which 

 develop from these have neither the structure nor the 

 instincts to enable them to do the work of the nest or to 

 procure food. Their part is to make raids on other fusca 

 nests, where they kill the adults so far as may be necessary 

 for their purpose of carrying off the fusca larvae and cocoons 

 to their own nest, the " slave " population of which is thus 

 kept up to the necessar}- level. The Amazons are, as has 

 frequently been remarked, '' absolutely dependent on their 

 slaves " for the maintenance of the community and the 

 survival of the race. Wheeler comments on their " two 



