THE COMPOl'XD NESTS. 



4 2 5 



which two different Colombian ants (Cremastogaster parabiotica and 

 Dolichodcrus dcbilis) were living together amicably, though keeping 

 their broods separate. The workers were seen leaving the nest in a 

 common file, which, however, eventually bifurcated, each species pro- 

 ceeding to its own feeding ground. This case, as Forel remarks, bears 

 some resemblance to the joint flocks of certain birds, like those of the 

 European Cori'iis corni.v and C. coronc. I nder the term parabiosis 

 may also be included the friendly or indifferent relations existing 

 between certain species of ants which I found inhabiting the epiphytic 







FIG. 255. Mound of Pogonomyrmex occidentalis showing at (a) a crater of Dory- 



niyrnic.r pyraniicus. (Original.) 



Tillandsias (especially T. bentliainiana ) on trees in Mexico, Florida 

 and the West Indies. These plants often contain whole colonies of 

 ants, with their larvae and pupae snugly packed away like so many 

 anchovies in the spaces between the moist, overlapping leaves. The 

 ants gnaw little holes through the leaves to serve as entrances to the 

 interfoliar chambers, and these holes often perforate several leaves 

 and extend to the very core of the bud-like plant. Sometimes a single 

 colony is divided up into companies, each occupying the space under a 

 leaf, but not infrequently two or even three flourishing colonies of as 

 many species may live in a single Tillandsia, the whole habitable por- 



