Chap. VIII.] SLAVE-MAKING- INSTINCT. 219 



burthened with booty, for about forty yards back, to a very thick 

 clump of heath, whence I saw the last individual of F. sanguinea 

 emerge, carrying a pupa ; but I was not able to find the desolated 

 nest in the thick heath. The nest, however, must have been close 

 at hand, for two or three individuals of F. fusca were rushing about 

 in the greatest agitation, and one was perched motionless with its 

 own pupa in its mouth on the top of a spray of heath, an image 

 of despair over its ravaged home. 



Such are the facts, though they did not need confirmation 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 continental F. vufcsccns. The latter does 

 not build its own nest, does not determine its own migrations, doe* 

 not collect food for itself or its young, and cannot even feed itself: 

 it is absolutely dependent on its numerous slaves. Formica san- 

 guinea, on the other hand, possesses much fewer slaves, and in the 

 early part of the summer extremely 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 larva?, 

 and the masters alone go on slave-making expeditions. In Switzer- 

 land 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 larva?. 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 the pupa? of other species, if scattered 

 near their nests, it is possible that such pupa? originally stored as 

 food might become developed ; and the foreign ants thus uninten- 

 tionally 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 advantageous to this 

 species to capture workers than to procreate them — the habit of 

 collecting pupa?, originally for food, might by natural selection be 

 strengthened and rendered permanent for the very different purpose 

 of raising slaves. When thi instinct was once acquired, if carried 

 out to a much less extent even than in our British F. sanguinea, 

 which, as we have seen, is less aided by its slaves than the same 

 • species in Switzerland, natural selection might increase and modify 



