PERFECT SOCIETIES OF INSECTS. 91 



the inhabitants of neighbouring formicaries, as is some- 

 times the case, attempt to make them their prey ; and car- 

 rying them about in their mouths to change their pasture, 

 or for some other purpose. When you consider that 

 from them they receive almost the whole nutriment both 

 of themselves and larvae, you will not wonder at their 

 anxiety about them, since the wealth and prosperity of 

 the community is in proportion to the number of their 

 cattle. Several other species keep Aphides in their nests, 

 but none in such numbers as those of which I am speak- 

 ing *. 



When the population exceeds the produce of a coun- 

 try, or its inhabitants suffer oppression, or aie not com- 

 fortable in it, emigrations frequently take place, and co- 

 lonies issue forth to settle in other parts of the globe ; and 

 sometimes whole nations leave their own country, either 

 driven to this step by their enemies, or excited by cupi- 

 dity to take possession of what appears to them a more 

 desirable residence. These motives operate strongly on 

 some insects of the social tribes. — Bees and ants are par- 

 ticularly influenced by them. The former, confined in a 

 narrow hive, when their society becomes too numerous to 

 be contained conveniently in it, must necessarily send forth 

 the redundant part of their population to seek for new 

 quarters; and the latter — though they usually can enlarge 

 their dwelling to any dimensions which their numbers 

 may require, and therefore do not send forth colonies, un- 

 less we may distinguish by that name the departure of the 



* See Huber, chap. vi. I have found Aphides in the nest of Myr- 

 mica rubra. Boisier de Sauvages speaks of ants keeping their own 

 Aphides, and gives an interesting account of them, Journ. de Phy- 

 iiqiie, i. lt)o. 



