358 ants' nests. 



4. — Combined Structures. 



The structures heretofore described are combined in a variety 

 of ways. 



For instance, the hollow stalk of a large Arcangelica is filled 

 from top to bottom with small earthen chambers by Lasius ?iiger 

 and occupied by them. Decayed trunks of trees are made use of 

 by ants which elsewhere build in the ground, excavated, and 

 worked up into nests by Lasius ?iiger, Lasius flavus, Formica fusca^ 

 Myr7?iica Icevinodis^ etc. Here wood dust and earth are used as 

 mortar in the construction of chambers and galleries. Formica 

 rufa, L., excavates the softer portions of the wood in half-decayed 

 trunks of trees, and build in them labyrinths which form a part of 

 its nests. 



Lasius brunneus, Latr., lives habitually in half-rotten trunks of 

 trees and beams, after excavating the moist, decayed wood. It 

 also lives in decayed woodwork in our houses, as do likewise fre- 

 quently Lasius umbratus, Ngl. 



The architecture of the group of forest ants — For7nica rufa, 

 L., prafensis, De Geer, truncicola, Nyl., exsecta, Ngl., and pressi- 

 labris, Nyl., as well as of their North American relatives, F. 

 exsecfoides, Forel, ititegra, Nyl., obscuripes, Forel, etc. — is, how- 

 ever, more imposing and more interesting. 



These ants mine the ground, but cover their nests with dry 

 vegetable matter of the most varied kinds — pine and fir cones, dry 

 leaves and pieces of wood, snail shells, little balls of rosin, blades 

 of grass ; in a word, with every kind of round and cylindrical 

 materials. With these they build the well-known immense 

 mounds, with their singular framework and the indescribable 

 interior labyrinth, the most thoroughly perforated part of which is 

 in the middle, at about the level of the ground. Earth serves 

 partially as cement. The openings of the nest are carefully closed 

 with small pieces of wood at night or when it is raining. They 

 are opened by the workers in the morning and generally in warm, 

 fine weather. 



The mound is gradually enlarged and strengthened by materials 

 dragged to it. It protects the interior perfectly against cold and 

 rain. 



