Chap. VII. SLAVE-MAKING INSTINCT. 223 



perched motionless with its own pupa in its mouth on 

 the top of a spray of heath over its ravaged home. 



Such are the facts, though they did not need confirma- 

 tion by me, in regard to the wonderful instinct of 

 making slaves. Let it be observed what a contrast the 

 instinctive habits of F. sanguinea present with those of 

 the F. rufescens. The latter does not build its own nest, 

 does not determine its own migrations, does not collect 

 food for itself or its young, and cannot even feed 

 itself : it is absolutely dependent on its numerous slaves. 

 Formica sanguinea, on the other hand, possesses much 

 fewer slaves, and in the early part of the summer ex- 

 tremely few. The masters determine when and where 

 a new nest shall be formed, and when they migrate, the 

 masters carry the slaves. Both in Switzerland and 

 England the slaves seem to have the exclusive care of 

 the larvse, and the masters alone go on slave-making 

 expeditions. In Switzerland the slaves and masters 

 work together, making and bringing materials for the 

 nest : both, but chiefly the slaves, tend, and milk as it 

 may be called, their aphides ; and thus both collect food 

 for the community. In England the masters alone 

 usually leave the nest to collect building materials and 

 food for themselves, their slaves and larvae. So that the 

 masters in this country receive much less service from 

 their slaves than they do in Switzerland. 



By what steps the instinct of F. sanguinea originated 

 I will not pretend to conjecture. But as ants, which are 

 not slave-makers, will, as I have seen, carry off pupae of 

 other species, if scattered near their nests, it is possible 

 that pupae originally stored as food might become de- 

 veloped ; and the ants thus unintentionally reared would 

 then follow their proper instincts, and do what work 

 they could. If their presence proved useful to the 

 species which had seized them — if it were more advan- 



