204 



ANTS. 



fully 30 cm. in height and do cm. to i m. in diameter. In the Rocky 

 Mountain region large mound nests of Pogonomyrmex occiiientulis, 

 l-'onnica obscnrif>cs. opacivent'ris and uryciitata abound, and in these 

 regions they are much needed for maturing the brood, as the nights are 

 cold in the summer and the heat of the daylight hours must be utilized. 

 / : <iriiiicii (jlticiiiiis, one of the varieties of I', fiisca, in .Maine, makes 



FIG. 112. Nest of Formica Integra in a huge pine stump, showing vegetable de- 

 tritus accumulated by the workers in the crevices of the bark and about the roots. 

 (Original.) 



true masonry domes like the European ants, and in this region such 

 nests must be very useful as incubators since the summers are short and 

 comparatively cool. 



I am able to confirm Ford's statement that in hilly or mountainous 

 regions ant-nests are most abundant on the eastern and southern 

 slopes. He says : " I have observed this repeatedly and also more re- 

 cently here in America. Here, too, the same explanation applies : The 

 morning sun awakens and urges the ants to work. During the after- 

 noon it is sufficiently warm so that this stimulus is unnecessary. Hence 



