33 2 ENTOMOLOGY 



Very many ants excavate their nests in the ground ; after 

 a rain these ants are especially industrious in the improvement 

 of the nest, pressing the wet earth into the walls of the gal- 

 leries and adding probably a secreted fluid which acts as a 

 cement; stones and sticks are often worked into the walls of 

 a nest and the mounds of ants are frequently fashioned about 

 blades of grass or growing herbage of whatever kind. The 

 subterranean galleries are often complex labyrinths ; frequently 

 there are long underground passages extending out in all direc- 

 tions, sometimes to aphid-infested roots of plants or, as in the 

 case of the leaf-cutting ants of the tropics, to trees which are 

 destined to be attacked; special chambers are set apart for the 

 storage of food and others for eggs, larvae or pupae. 



Often a nest is excavated under a stone. As Forel ob- 

 serves, the stone warms speedily under the rays of the sun, 

 and in damp or cool weather the ants are always in the highest 

 story of the nest as soon as the sun's warmth begins to pene- 

 trate the soil, while they go below as soon as the sun disap- 

 pears or when its heat becomes too strong. They select stones 

 that are neither too large nor too small to regulate the tem- 

 perature well, while other ants attain the same object by mak- 

 ing the nest under sheltering herbage or by making a mound 

 with a hard cemented roof. 



The well-known ant-hills may consist simply of excavated 

 particles of soil or else, as in the huge mounds of Formica 

 exscctoides, may contain labyrinthine passages in addition to 

 those underground. The mounds of this species are elaborate 

 structures which may last a man's lifetime at least. F. exsec- 

 toides is accustomed to form new colonies in connection with 

 the parent nest ; McCook found in the Alleghanies no less than 

 i, 600 nests, forming a single enormous community with hun- 

 dreds of millions of inhabitants, hostile to all other colonies of 

 ants, even those of the same species. This ant covers its 

 mound with twigs, dead leaves, grass and all sorts of foreign 

 material, and is said to close the exits of the nest with bits of 

 wood at night and in rainy weather, removing them in the 

 morning or when the weather becomes favorable. 



