1951 ] 
Creighton — Arizona Ants 
93 
lower slopes of Carr Peak. In this same area were taken 
representatives of typically northern ant groups (Polyer- 
gus, Myrmica, Raptiformica, Camponotus sen. str., Stenam- 
ma, etc.). Since the Sonoran elements of the evergreen 
oak belt are absent at these elevations, the ant fauna above 
the 7000 foot level has an entirely different character from 
that of the 6000 foot level. Its affinities are Transitional 
or Canadian and the presence of huachucana in this associa- 
tion offers a good demonstration that this insect belongs 
with the northern elements of the biota. It may be added 
that all the nests of huachucana, including the type nest, 
were situated on steep slopes. They were placed in shady 
aspen groves, in the lighter shade of pine groves or in full 
sun. Some were built in the soil under a covering stone, 
others in the soil which had accumulated between the stones 
in a rock slide. In view of the fact that texana is quite 
fussy about its nest sites, the greater tolerance of huachu- 
cana in this respect is surprising. 
What is even more surprising is that the range of these 
two species should be so clearly separated by so small an 
amount of space. It should be plain from the discussion 
just presented that there is an elevational gap of some five 
hundred feet between the lower edge of the range of 
huachucana and the upper edge of the range of texana. 
The distance involved is such a minor one that it could 
not conceivably be a direct barrier to movement in either 
direction, particularly to winged females. We must sup- 
pose, therefore, that the gap between the ranges exists 
not because either species is unable to enter it but because, 
when they have done so, each species finds the area un- 
suitable as a situation for a successful nest. Both huachu- 
cana and texana (at least that part of its population which 
occurs in the Huachucas) have developed a degree of en- 
vironmental restriction which isolates the two species as 
effectively as though their ranges were separated by 
hundreds of miles. In view of the actual proximity of the 
ranges one may inquire how this isolation can be main- 
tained. There is every reason to believe that at the time 
of nuptial flight, many males and females of each species 
reach the range of the other species. If the nuptial flight 
