154 HYMENOPTERA CHAP. 



selves thus assaulted and besieged, communicated in some way, 

 information of the fact to the neighbouring colonies, and Forel 

 soon saw large columns of the black creatures issuing from the 

 trees near by and coming with their measured paces to the 

 assistance of their confreres, so that the invaders were soon dis- 

 comfited and destroyed. Although the European and North 

 American representatives of the sub-family Camponotides live 

 together in assemblies comprising as a rule a great number of 

 individuals, and although the separate nests or formicaries which 

 have their origin from the natural increase of a single original 

 nest keep up by some means a connection between the members, 

 and so form a colony of nests whose inhabitants live together on 

 amicable terms, yet there is no definite information as to how 

 long such association lasts, as to what is the nature of the ties 

 that connect the members of the different nests, nor as to the 

 means by which the colonies become dissociated. It is known that 

 individual nests last a long time. Charles Darwin has mentioned 

 in a letter to Forel that an old man of eighty told him he had 

 noticed one very large nest of Formica rufa in the same place 

 ever since he was a boy. But what period they usually endure 

 is not known, and all these points probably vary greatly according 

 to the species concerned. It has been well ascertained that when 

 some ants find their nests, for some unknown reason, to be unsuit- 

 able the inhabitants leave their abodes, carrying with them their 

 young and immature forms, and being accompanied or followed by 

 the various parasites or commensals that are living with them. 

 Wasmann and other entomologists have observed that the ants 

 carry bodily some of their favourite beetle-companions, as well 

 as members of their own species. Forel observed that after 

 a nest of Formica pratensis had been separated into two nests 

 placed at a considerable distance from one another so as to have 

 no intercommunication, the members yet recognised one another 

 as parts of the same family after the lapse of more than a month ; 

 but another observation showed that after some years of separation 

 they were no longer so recognised. 



Although it is now well ascertained that ants are able to 

 distinguish the individuals belonging to their own nests and 

 colonies from those that, though of their own species, are not so 

 related to them, yet it is not known by what means the recogni- 

 tion is effected ; there is, however, some reason to suppose that it 



