THE SAXGi'IXARY ANTS. 457 



that the colony has acquired a knowledge of the precise location of 

 the various nests of the slave species within an area of a hundred 

 meters or more of its own nest. This knowledge is probably acquired 

 by scouts leaving the nest singly and from time to time for a period of 

 several weeks, and these scouts must be sufficiently numerous to deter- 

 mine the movements of the whole worker body when it leaves the nest. 

 This presupposes not only a high development of memory, but some 

 form of communication, for the nest attacked is usually one of main- 

 lying in different directions from the sangninca nest. 



When the first workers arrive at the nest to be pillaged, they do not 

 enter it at once, but surround it and wait till the other detachments 

 arrive. In the meantime the fusca or rnfibarbis scent their approach- 

 ing foes and either prepare to defend their nest or seize their young 

 and try to break through the cordon of sangninca and escape. They 

 scramble up the grass-blades with their larvae and pupae in their jaws 

 or make off over the ground. The sanguinary ants, however, intercept 

 them, snatch away their charges and begin to pour into the entrances 

 of the nest. Soon they issue forth one by one with the remaining 

 larvae and pupae and start for home. They turn and kill the workers 

 of the slave-species only when these offer hostile resistance. The troop 

 of cocoon-laden sanguined straggle back to their nest, while the bereft 

 ants slowly enter their pillaged formicary and take up the nurture of 

 the few remaining young or await the appearance of future broods. 



Forel is of the opinion that many of the young brought home by the 

 sanguined are eaten, for the number of those which eventually hatch 

 and become auxiliaries is very small compared with the number pillaged 

 during the course of the summer. Wasmann believes, however, that the 

 forays take place for the specific purpose of obtaining young to rear. 

 This seems to be disproved by the fact that even small san guinea colo- 

 nies are quite able to get along without slaves and by the insignificant 

 number of these individuals in many nests. Darwin has interpreted 

 the surviving and adopted workers as a kind of by-product, or as rep- 

 resenting food which the ants failed to eat at the proper time, and such 

 they would appear to be in the adult colony, though, as we shall see, 

 they have an additional significance as the result of an instinct inherited 

 by the sanguinea workers from their queen. That the foray is, to 

 some extent at least, due to the promptings of hunger, seems to be 

 shown by the fact that sanguinea sometimes plunders the nests of ants 

 which it could not adopt as slaves. Thus Forel and others have 

 described forays of sanguinea on Lasius mgcr and ftavus. 



Not only are the forays of sangninca very similar to those of the 

 nest-pillaging Ecitons, but the former ant also resembles the rapacious 



