A \T-XESTS. 2or 



care. It is at once restored or rebuilt after destruction by rain or wind. 

 In sandy regions most ants carry out the sand-grains one by one and 

 deftly lay them on the walls of the crater. Among the Attii, however, 

 the excavated sand is moulded into large polygonal pellets of uniform 

 size in which the grains are agglutinated by moisture. 



What I have called small craters vary from a couple of centimeters 

 to 10 or 15 cm. in diameter. They are constructed by many of our 

 species of Phcidolc, Alyn/iica and Prenolepis, by Lasius aincricanns, 

 Dor\in\nnc.\' pyramicus, Monomorium minimum, Camponotus anieri- 

 caniis and by the smaller species of P.ogonomyrmex, Mynnccocystiis 

 (Fig. 107), etc. These craters vary greatly in size and shape, some be- 

 ing very flat and ring-like, with a clear space between the central open- 

 ing and the crater wall (Xylandcria arciiiz'a^a), others very high and 

 narrow, and almost chimney- or tower-shaped, with the opening on the 

 summit (Trach-\mynnc.\- turrifc.r, M ycctosoritis hartinani and Lasius 

 aincricanns}. In some species there are numerous craters corresponding 

 to as many nest entrances, and the walls of these craters may be strung 

 along in a series (Phcidolc rinclandica] or more or less fused with one 

 another (Ph. dcntata and inorrisi, Solcnopsis gcniinata}. 



Large craters, from 20-50 cm. or even more in diameter, are con- 

 structed by several of our North American ants, notably by Atta 

 tc.rana, Mccllcrius 1'crsicolor, Isclinoinyrinc.r cockcrclli (Fig. 156), ^les- 

 sor pergandci (Fig. 152), Poyonoinyrinc.v badius, comanchc and cali- 

 fornicus, Myrmccocystus inclli^cr and hortideorum, and several species 

 of Formica (F. schaufitssi, iinimla, snbpolita, etc.). These craters, 

 especially in Formica, may be multiple and fused with one another like 

 the small craters, and thus form extensive flattened elevations, perforated 

 with openings (F. subscricca, ncoclara. ueocincra, etc.) . It has been sug- 

 gested that the craters, though consisting of materials brought to the 

 surface and rejected during excavation, may nevertheless be of use to 

 the ants in protecting their nest entrances from the wind. Forel has 

 observed that the walls of the craters of certain desert ants, like Alessor 

 arcnarins of the Sahara, are raised to a greater height on the windward 

 side. 



Just as it is difficult to make anything more than a purely artificial 

 distinction between small and large crater nests, so it is by no means 

 easy to distinguish certain large craters from mound, or hill nests. The 

 latter are usually much larger than the craters, not because they repre- 

 sent more extensive excavation in the underlying soil, but because they 

 represent a large amount of material collected by the workers from the 

 territory surrounding the nest. This accumulation is perforated 

 throughout with ga 1 leries and chambers and consists of earth, small 



