200 



ANTS. 



to conceal tin- situation of their nests. The excavated soil pellets are 

 therefore carried sonic distance from the nest opening and scattered 

 about irregularly, and the entrance itself is often kept closed with a few 

 pebbles or so adroitly concealed in a tuft of grass or under a prostrate 

 leaf that it is impoible to find the nest without carefully following 

 some- worker that happens to be returning from a foraging excursion. 

 This habit of concealment is retained even by adult colonies of timid 

 species I /)ichotln -u.r and Lcptothoni.v ). Sometimes the earthen pel- 

 let- are scattered over a wide circular area so as to produce what may 



FIG. no. Formica nifa nest 2.15 meters high and 9.8 meters in diameter; pine 

 forests of Belgium. (Photograph by G. Severin.) 



be called a rudimental crater (Mynnecocystns mojare and Aphccno- 

 t/astcr trcattc. ) Another form of rudimental crater is seen in species 

 like Trach\ui\rme.\- septentrionalis, which dumps all the excavated soil 

 in an elliptical or crescentric heap at a distance of several inches from 

 the opening', and in Pogonomyrmex occidentals and calif oj-nicns, which, 

 on first establishing their nests, arrange the soil in a fan-shaped sector 

 at the opening (Fig. 165,^). In older nests of these ants the crater is 

 completed by the gradual enlargement of the sector along its radii and 

 arc till it becomes a circle (Fig. 165,5). The typical crater which is the 

 commonest form of ant-nests in regions devoid of stones and is best 

 developed in light soil or pure sand, is often constructed with exquisite 



