42 HISTORY OF INSECTS. 



Although the hillock when complete appears but a care- 

 less heap, it is in reality a most ingenious device for keep- 

 ing out water, for evading the effects of wind, and the 

 attacks of enemies, and yet more especially for receiving 

 and husbanding the heat of the sun. The exterior of the 

 hillock always presents the appearance of a dome ; the base 

 being covered with earth and minute pebbles, the struc- 

 ture is completely hidden from us. From the summit of 

 the hillock, avenues carefully excavated like tunnels lead 

 downwards into the interior, and the number of these ave- 

 nues depends entirely on the population and extent of the 

 nest : the external apertures of these avenues are of varied 

 size ; there is sometimes a principal one at the top ; but 

 usually there are several somewhat unequal ones, and 

 around each are passages symmetrically arranged. These 

 apertures are required to permit free egress to the mul- 

 titudes of labourers of which the commonwealth is com- 

 posed : not only do the needful labours of the commu- 

 nity continually call them abroad, but they seem to prefer 

 labouring in the open air, and, moreover, appear perfectly 

 unconcerned at the presence of an observer ; in this the 

 yellow ants differ from most other species, which often use 

 their habitation as a protection from the sun. 



In the habitations of several species of ants, we never 

 find an aperture of sufficient size to allow the entrance of 

 enemies, or permit rain-water to penetrate. The dome, 

 commonly of earth, is closed on every side, and has no 

 aperture unless near the base, and not unfrequently the 

 ants approach the nest by a serpentine gallery, many feet 

 in extent. The yellow ants standing in crowds on their 

 nest during the day, are quite fearless of any disturbance 

 to the interior ; but at night when retired to the bottom of 

 their habitation, they cannot perceive what is passing on 

 the exterior : how then are they protected from the acci- 



