-I -'I ANTS. 



together in a single nc-t and bring up their young in common. Although 

 each of these categoric.- comprises a number of dissimilar types of social 

 symbiosis, and although it is possible, under certain circumstances, as 

 will IK- shown in the sequel, to convert a compound nest into a mixed 

 colony, the distinction is nevertheless fundamental. It must be admitted, 

 however, that both types depend in last analysis on the dependent, 

 adoption-seeking instincts of the queen ant and on the remarkable 

 plasticity which enables allied species and genera to live in very close 

 proximity to one another. By a strange paradox these peculiarities 

 have been produced in the struggle for existence, although this struggle 

 is severer among different species of ants than between ants and other 

 organisms. As Forel says: "The greatest enemies of ants are other 

 ants, just as the greatest enemies of men are other men." And just 

 as the homo homini lupus may wear many a pleasing disguise, so the 

 formica funnicfc lnf>a may secure the aid or protection of another spe- 

 cies of ant by exhibiting an engaging demeanor. This will be more 

 apparent when we come to the cases of the mixed colonies. In the 

 present chapter my remarks will be confined to the compound nests, 

 with a brief consideration of the various known cases. 



A. Plesiobiosis. I have given this name (igoic) to the cases in 

 which two or more colonies of different species of ants or of ants and 

 termites establish their nests in contiguity or very close proximity, as 

 often happens under the same stone. These are the double, triple, 

 etc., nests of Forel (1874) and represent the most rudimental form of 

 social symbiosis. The species nesting in this manner are either 

 indifferent or hostile to one another, as may be readily observed 

 by their behavior when the stone is removed and the walls between 

 the nests broken asunder so that the insects can meet face to face, 

 or one of the species is timid or hypogaeic in its habits. Two or 

 more aggressive species can hardly live under the same stone, as 

 their nest entrances would be necessarily so close together that the 

 insects would be apt to encounter one another continually while enter- 

 ing or leaving the nest. I have never found two well-developed colo- 

 nies of the same species under the same stone. Indeed, such a condition 

 could hardly be maintained for 'any length of time, since the colonies 

 would in all probability either become friendly and fuse into one, or 

 would fight till one was compelled to seek quarters elsewhere. The 

 fact that different species are able to live in plesiobiosis is probably 

 due to differences of habit of sufficient magnitude to diminish or temper 

 somewhat the struggle for existence. 



B. Parabiosis. This term was introduced by Forel (18986) to des- 

 ignate a peculiar type of compound nest with inosculating galleries in 



