Chap. X. HYMENOPTERA. 365 



mind that insects belonging to this Order have the 

 power of recognising each other after long intervals of 

 time, and are deeply attached. For instance, Pierre 

 Huber, whose accuracy no one doubts, separated some 

 ants, and when after an interval of four months they 

 met others which had formerly belonged to the same 

 community, they mutually recognised and caressed each 

 other with their antennae. Had they been strangers 

 they would have fought together. Again, when two 

 communities engage in a battle, the ants on the same 

 side in the general confusion sometimes attack each 

 other, but they soon perceive their mistake, and the 

 one ant soothes the other. 55 



In this Order slight differences in colour, according 

 to sex, are common, but conspicuous differences are 

 rare except in the family of Bees; yet both sexes of 

 certain groups are so brilliantly coloured — for instance 

 in Chrysis, in which vermilion and metallic greens 

 prevail — that we are tempted to attribute the result 

 to sexual selection. In the Ichneumonidaa, according to 

 Mr. Walsh, 56 the males are almost universally lighter 

 coloured than the females. On the other hand, in the 

 Tenthredinidse the males are generally darker than the 

 females. In the Siricidse the sexes frequently differ; 

 thus the male of Sirex juvencus is banded with orange, 

 whilst the female is dark purple ; but it is difficult to 

 say which sex is the most ornamented. In Tremex 

 columbte the female is much brighter coloured than the 

 male. With ants, as I am informed by Mr. F. Smith, 

 the males of several species are black, the females 

 being testaceous. In the family Of Bees, especially in 



55 P. Huber, ' Recherches sur les Moeurs des Fourmis,' 1810, p. 150, 

 165. 



56 ' Pi-oc. Eutomolog. Soc. of Philadelphia,' I860, p. 238-239. 



