ANTS' HABITATIONS 



137 



number of subterranean chambers, often under the shelter of a 

 stone, and connected by galleries. It is of course very difficult to 

 trace exactly the details of such a work, because when excavations 

 are made for the purposes of examination, the construction becomes 

 destroyed ; it is known, however, that some of these systems 

 extend to a considerable depth in the earth, it is said to as much 

 as nine feet, and it is thought the object of this is to have access 

 to sufficiently moist earth, for ants are most sensitive to variations 

 in the amount of moisture ; 



a quite dry atmosphere is in ^"^teSi -. c?^, f 



the case of many species very 

 speedily fatal. This system 

 of underground labyrinths 

 is sometimes accompanied by 

 above-ground buildings con- 

 sisting of earth more or less 

 firmly cemented together by 

 the ants ; this sort of dwell- 

 ing is inOSt frequently adopted FlG . 58. Portion of combined nest of For- 



mica fusca and Solenopsis fugax. (After 

 Forel.) x|. /,/', Chambers of Formica, 

 recognisable by the coarser shading ; 

 s, s' t chambers of the Solenopsis (with 

 finer shading) ; s", opening in one of the 

 chambers, the entrance to one of the 

 galleries that connects the chambers of the 

 Solenopsis; w, walls forming the founda- 

 tions of the nest and the limits of the 

 chambers. 



when the soil in which the 

 nests are placed is sandy ; it 

 is probable that the earth is 

 in such cases fastened together 

 by means of a cement pro- 

 duced by the salivary glands 

 of the ants, but this has not 

 been determined with certainty ; vaulted galleries or tunnels of 

 this kind are constructed by many species of ants in order to 

 enable them to approach desired objects. 



In South America Camponotus ruftpes and other species that 

 habitually dwell in stumps, in certain districts where they are 

 liable to inundations, build also nests of a different nature on 

 trees for refuge during the floods. In Europe, a little robber-ant, 

 Solenopsis fugax, constructs its dwelling in combination with that 

 of Formica fusca (Fig. 58), in such a manner that its chambers 

 cannot, on account of the small size of the orifices, be entered by 

 the much larger Formica. Hence the robber obtains an easy 

 living at the expense of the larger species. The Sauba or Sauva 

 ants of South America (the genus Atta of some, Oecodoma of 

 other authors) appear to be most proficient in the art of sub- 



