MOUNTAIN ANTS OF NORTH AMERICA. 459 



ants are therefore usually observed to return in great numbers to the 

 ground at no great distance from their parental nests. 



The height to which ants are able to ascend on their nuptial flights 

 will be ascertained only when some of our young myrraecologists 

 become aviators. We know that winged ants are often carried to high 

 mountain peaks. Forel (1874) records the occurrence of males and 

 females of Formica rvfa and -pratensis on the perpetual snows of Alpine 

 glaciers, and Mrs. Slosson sent me several male and female ants of 

 different genera from the summit of Mt. Washington, N. H. (Wheeler 

 1905). I have myself taken similar specimens on the summits of 

 other peaks in the White Mountains. But, as Forel has shown, female 

 ants never succeed in establishing colonies at these altitudes. They 

 are merely transported to the summits by the air-currents which are 

 known to ascend mountain slopes during the day-time and to carry up 

 great numbers of insects of all orders. Unless, therefore, such females 

 were able to descend on the opposite slopes, — and this is probably of 

 very rare occurrence — high mountain ranges must constitute barriers 

 as effective as are considerable bodies of water or deserts to the dis- 

 tribution of most ants. I am convinced that the Sierra Nevada in 

 California is such a barrier to many forms common on the Pacific 

 Coast and in Europe the Alps certainly act as a similar barrier to many 

 species common in Italy and Central Europe. 



For the purpose of bringing before the reader as clearly as possible 

 the results of my study of the ants of the Transition and Canadian 

 Zones, I have cited the various species, subspecies and varieties from 

 the Coast Range of California, the Sierra-Cascade Ranges, the Rocky 

 Mountains and the portion of North America east of these ranges in 

 four columns in the accompanying Tables I to IX (pp. 464 to 481). 

 As might be expected, the great ranges of the Rocky Mountains, 

 from British America to Mexico, show the greatest number and 

 diversity of forms. The Eastern portion of North America has, with 

 the exception of a certain number of holarctic and neotropical species, 

 a fauna peculiar to itself, and the Sierras and Californian Coast each 

 possesses peculiar elements, though also possessing many forms in com- 

 mon with the Rocky Mountains. One is struck in the tables by the 

 meagerness of the two Californian mountain faunas. This might be 

 attributed to their much smaller territory, but such can hardly be a 

 complete explanation, for ant-colonies in California, even those of the 

 more dominant species, are much less numerous than they are in the 

 Rocky Mountains and Eastern States. I believe that the difference 

 is due to the peculiar annual distribution of temperature and mois- 



