SLAVE-MAKING INSTINCT 275 



as yet been perfected; for a surprising number of eggs lie 

 strewed over the plains, so that in one day's hunting I picked 

 up no less than twenty lost and wasted eggs. 



Many bees are parasitic, and regularly lay their eggs in the 

 nests of other kinds of bees. This case is more remarkable 

 than that of the cuckoo; for these bees have not only had 

 their instincts but their structure modified in accordance with 

 their parasitic habits ; for they do not possess the pollen- 

 collecting apparatus which would have been indispensable if 

 they had stored up food for their own young. Some species 

 of Sphegidae (wasp-like 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 advanta;^e 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 selec- 

 tion 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 

 discovered 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 inconvenient, and they 

 have to migrate, it is the slaves which determine the migra- 

 tion, 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 

 Vv'hich they like best, and with their own larvae and pupre 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 



