232 



PSYCHE. 



[August, 1901 



makes large, elevated conical mounds of 

 earth in the forests. I visited two of 

 these colonies in the vicinity of Worces- 

 ter and of Black Mountain. The nests 

 open by holes situated at the base and 

 about the periphery. The workers do 

 not make excavated roads like our rufa 

 of Europe. 



Besides these, Formica fitsca, r. stih- 

 scricca and paUidcfulva rarely make 

 small mounds. As for snbscricia, so 

 common everywhere, I have seen its 

 mounds only at Niagara, at the side of 

 the fall. 



After mature reflection I have come 

 to the conclusion that this singular fact 

 does not seriously weaken my theory of 

 the domes, but rather confirms it. In 

 my " Fourmis de la Suisse," I have 

 shown that the elevated dome is used by 

 our ants to collect and concentrate on 

 their larvae the radiant solar heat which 

 they so much need, and I cited a num- 

 ber of facts in support of this view. But 

 the climate of North America is entirely 

 different from ours. Extremely cold in 

 winter, it is burning in summer; there 

 are extremes of which we in Europe 

 have no idea. The ants consequently 

 have quite enougli heat and sunlight 

 for their larvae. The dome is superflu- 

 ous. What they do need is protection 

 from extreme temperatures. For this 

 purpose it is necessary either to mine 

 deeply or to_ locate themselves in the 

 shade and in the decaying trunks of 

 forest trees. And that is what they do. 

 At least it is in this way that I explain 

 most readily this fact, so surprising by 

 its generality. 



Another fact to which Blochmann first 

 called attention in Europe in connection 

 with Camponotus ligniperdus is the follow- 

 ing : The nests of ants abound above all 

 on hill-slopes facing the east. I have con- 

 firmed this statement since then many a 

 time, and here in America again. In 

 this case also the explanation seems 

 simple : The morning sun awakens the 

 ants and urges them to work. After 

 noon it is warm enough, they no longer 

 need the sunshine. Hence the advan- 

 tage of an easterly exposure which pro- 

 vides for a large amount of daily activity. 

 Toward the west, on the contrary, they 

 would lose the first hours of the morning, 

 would be unable to work on account of 

 the heat after noon in summer, and 

 could do next to nothing in the evening 

 to make up for it, once the night was 

 come. Moreover, the night equalizes 

 very quickly the eastern and western 

 exposures, so that the latter do not even 

 prolong the afternoon's activity among 

 those species which work at night. 

 Ants, then, have every advantage in 

 securing sunshine in the morning and 

 shade in the afternoon — in America as 

 in Europe. 



Let us pass on to some particular 

 cases. 



The species of Fonniia of Europe have 

 American representatives. To F. rufa, 

 prafensis, truncicola and exsecta of Europe 

 correspond integra, ohscurifer, ahsairii'eii- 

 tris and cxsecioidcs of America. We 

 have seen that exsedoides is the only ant 

 of eastern America which makes large 

 domes. It lives in colonies of five to 

 twenty nests. McCook has seen 1500 



