354 SEXUAL SELECTION. [Part II. 



which had formerly belonged to the same community, 

 they mutually recognized 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 confu* 

 sion sometimes attack each other, but they soon perceive 

 their mistake, and the one ant soothes the other. 66 



In this order slight differences in color, according to 

 sex, are common, but conspicuous differences are rare ex- 

 cept in the family of Bees ; yet both sexes of certain 

 groups are so brilliantly colored — for instance, in Chrysis, 

 in which vermilion and metallic greens prevail — that we 

 are tempted to attribute the result to sexual selection. In 

 the Ichneumonidae, according to Mr. Walsh, 66 the males 

 are almost universally lighter colored than the females. 

 On the other hand, in the Tenthredinidse the males are 

 generally darker than the females. In the Siricidae the 

 sexes frequently differ : thus the male of Sirexjuvencus is 

 banded with orange, while the female is dark purple ; but 

 it is difficult to say which sex is the most ornamented. 

 In Tremex colwmboe the female is much brighter colored 

 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 

 the solitary species, as I hear from the same distinguished 

 entomologist, the sexes often differ in color. The males 

 are generally the brightest, and, in Bombus as well as in 

 Apathus, much more variable in color than the females. 

 In Anthophora retusa the male is of a rich fulvous brown, 

 while the female is quite black : so are the females of sev- 

 eral species of Xylocopa, the males being bright yellow. 

 In an Australian bee (Lestis bombylans), the female is of 



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

 150, 165. 



M 'Proc. Entomolog. Soc. of Philadelphia,' 1866, pp. 238, 239. 



