MOUNTAIN ANTS OF NORTH AMERICA. 401 



This preference of our northern ants for eastern and southern slopes 

 is further confirmed by the shape of the nest and the position of the 

 nest-entrance of certain species. This matter was considered in my 

 ant-book (1910, p. 205) in the following passage: "I have already 

 called attention to the constant position of the nest opening at the 

 base of the southern or eastern slope of the mounds of Pogonomyrmex 

 occidentalis. Huber says that the yellow ants {Lasius flavus) of 

 Switzerland "serve as compasses to the mountaineers when they are 

 enveloped in dense fogs or have lost their way at night; for the reason 

 that the nests, which in the mountains are much more numerous and 

 higher than elsewhere, take on an elongated, almost regular form. 

 Their direction is constantly from east to west. Their summits and 

 more precipitous slopes are turned towards the winter sunrise, their 

 longer slopes in the opposite direction." These remarks of Huber 

 have been recently confirmed by Tissot (Wasmann 1907) and Linder 

 (1908). The latter has shown that the elongate shape of the mounds 

 is due to the fact that the ants keep extending them in an easterly 

 direction in such a manner that only the extreme easterly, highest and 

 most precipitous portions are inhabited by the insects. I have 

 observed a similar and equally striking orientation of the mounds of 

 Formica argentata [fusca var. argtmtea] in the subalpine meadows of 

 Colorado." In the southern hemisphere, as we should expect, the 

 ants prefer the northern and eastern slopes of the mountains. I found 

 many striking instances of this preference while collecting in the moun- 

 tains of New Zealand, New South Wales and Queensland. 



Merriam and his collaborators in their studies of the floras and 

 faunas of the mountains of western North America have published 

 interesting observations which deserve consideration since they have a 

 bearing on the distribution of the Formicidae though they show that 

 these insects would hardly suffice to determine the boundaries of the 

 various life-zones on mountain slopes. In his work on Mt. Shasta, 

 Merrian (1899) says: "The influence of slope exposure on the faunas 

 and floras of mountain regions is profound. Measured by a scale of 

 altitudes it amounts on ordinary slopes to nearly a thousand feet and 

 on steep slopes is still more marked. Thus on mountains it is usual 

 for plants and animals of particular species to occur on warm south- 

 westerly slopes at elevations 800 to 1000 feet higher than on cool 

 northeasterly slopes — similarly on north and south ridges, the fauna 

 and floras of the warm west slopes often belong to lower zones than 

 those of equal elevations on the cool east slopes." Merriam had pre- 

 viously shown the existence of very similar conditions in a very differ- 



