CHAPTER XXV. 



Till-: SAXGflXARY ANTS, OR FACULTATIVE SLAVE-MAKERS. 



" I shall next bring forward a scene still more astonishing, which at first, 

 perhaps, you will be disposed to regard as the mere illusion of a lively imagina- 

 tion. What will you say when I tell you that certain ants are affirmed to sally 

 forth from their nests on predatory expeditions, for the singular purpose of pro- 

 curing slvi'cs to employ in their domestic business; and that these ants are 

 usually a ruddy race, while their slaves themselves are black." Kirby & Spence, 

 " Entomology," 6th ed., 1846. 



" Cc fait choquant et hideux, tachons du moins de le comprendre. II est 



propre a quelques especes ; il est un incident particulier, mi cas exceptionnel, 



mais rentrant an total dans une loi generale de la vie des fourmis." Michelet, 

 "L'Insecte," 1884. 



The mixed colonies described in the last chapter are transitory 

 consociations of two species merely formed as a means of establishing 

 colonies, which, in their adult stages, are able to hold their own unaided 

 in the struggle for existence. The cases to be described in this and 

 the following chapters are more permanent symbiotic alliances, though 

 they differ so much among themselves that it is difficult to include them 

 in a single definition. With one or two exceptions, to be described in 

 their proper places, these mixed colonies may be said to be formed by 

 dulosis, or slavery, and this peculiar phenomenon may be defined as 

 the habit of making periodical raids on particular alien species, seizing 

 their worker larvse and pupae and rearing and adopting a portion of 

 these. But neither the periodical raid nor the rearing of the alien 

 ants alone constitutes slavery. Many of the species of Eciton make 

 such raids on other ants and pillage their nests, but they attack any 

 terrestrial ants indiscriminately and the young are all devoured. And 

 even if some of these were permitted to hatch, a mixed colony would 

 not result, because the Ecitons have no fixed home, but wander from 

 place to place. Moreover, although the mixed dulotic colony certainly 

 owes its origin to the rearing and adopting of the alien young, many 

 nondulotic ants will do this if such young are placed in or near their 

 nests. Forel (1874) long ago formed mixed colonies in this way, 

 and more recently Miss Fielde ( i9O3f ) has shown the extreme to 

 which this experiment can be carried. She succeeded in making 

 triple and quadruple mixed colonies of ants belonging not only to 

 different genera, but also to different subfamilies (Fig. 266). One 



