202 SPECIAL INSTINCTS. [CHAP. VHL 



insects) are likewise parasitic ; and M. Fabre has lately shown 

 good reason for believing that, although the Tachytes nigra 

 generally makes its own burrow and stores it with paralysed prey 

 for its own larvae, yet that, when this insect finds a burrow already 

 made and stored by another sphex, it takes advantage of the 

 prize, and becomes for the occasion parasitic. In this case, as 

 with that of the Molothrus or cuckoo, I can see no difficulty in 

 natural selection making an occasional habit permanent, if of 

 advantage to the species, and if the insect whose nest and stored 

 food are feloniously appropriated, be not thus exterminated. 



Slave-making instinct. This remarkable instinct was first dis- 

 covered in the Formica (Polyerges) rufescens by Pierre Huber, a 

 better observer even than his celebrated father. This ant is 

 absolutely dependent on its slaves ; without their aid, the species 

 would certainly become extinct in a single year. The males and 

 fertile females do no work of any kind, and the workers or sterile 

 females, though most energetic and courageous in capturing slaves, 

 do no other work. They are incapable of making their own nests, 

 or of feeding their own larvae. When the old nest is found incon- 

 venient, and they have to migrate, it is the slaves which determine 

 the migration, and actually carry their masters in their jaws. So 

 utterly helpless are the masters, that when Huber shut up thirty 

 of them without a slave, but with plenty of the food which they like 

 best, and with their own larvse and pupse to stimulate them to 

 work, they did nothing ; they could not even feed themselves, and 

 many perished of hunger. Huber then introduced a single slave 

 (F. fusca), and she instantly set to work, fed and saved the 

 survivors ; made some cells and tended the larvae, and put all to 

 rights. What can be more extraordinary than these well-ascer- 

 tained facts 1 If we had not known of any other slave-making ant, 

 it would have been hopeless to speculate how so wonderful an 

 instinct could have been perfected. 



Another species, Fonnica sanguinea, was likewise first discovered 

 by P. Huber to be a slave-making ant. This species is found in 

 the southern parts of England, and its habits have been attended 

 to by Mr. F. Smith, of the British Museum^ to whom I am much 

 indebted for information on this and other subjects. Although 

 fully trusting to the statements of Huber and Mr. Smith, I tried 

 to approach the subject in a sceptical frame of mind, as any one 

 may well be excused for doubting the existence of so extraordinary 

 an instinct as that of making slaves. Hence, I will give the obser- 

 vations which I made in some little detail. I opened fourteen 

 nests of F. sanguinea, and found a few slaves in all. Males and 

 fertile females of the slave species (F. fusca) are found only in their 

 own proper communities, and have never been observed in the 

 nests of F. sanguinea. The slaves are black and not above half 



