32 
Psyche 
[Vol. 88 
Results 
Nest structure. 
The nest of P. montanus has numerous burrows in the upper 
levels (Figure 1). Below this, there is often only a single main tunnel 
to the bottom of the nest. Most of the ants are found in the burrows 
which branch from the main tunnel. The main tunnel contains few 
ants and is apparently used only for movement between the side 
burrows. In many cases there are two separate “major tunnels”, as is 
shown in Figure 1. In P. subnitidus the two major tunnels may be 
separated by more than 100 cm and may appear as two separate 
nests. One major tunnel may contain no brood and the other may 
contain all of the brood in the nest. The queen and brood are usually 
found in the major tunnel which goes to the deeper level. 
The structure of the nests of P. subnitidus and P. rugosus are not 
shown, but are similar except that they are larger and deeper, often 
extending to 300 or 400 cm deep. There was no relationship between 
the worker populations and the nest depth (for P. montanus r = 
0.16ns (65), for P. subnitidus r = 0.03ns (26), and for P. rugosus r = 
0.32ns (20)). 
Nest microclimatology: temperature. 
The seasonal changes in nest temperatures are similar for all three 
species (Figure 2). The nest warms rapidly in the spring and 
temperatures reach a maximum at the end of June or July. The soil 
temperature begins to drop in August and levels out during the 
winter months. As the species occur at different altitudes, the 
temperature ranges are different. The range of P. montanus extends 
from slightly below zero to 20° C, that of P. subnitidus from slightly 
above zero to 25° C, and that of P. rugosus from slightly below 10 
to 30° C. 
Only the changes at the 20 and 50 cm depths are shown in Figure 
2 as the other levels are similar. The differences between the levels 
deeper than 40 cm were generally not significant. The only 
important difference between the curves of the 20 cm level and 50 
cm level is that the shallow level warmed sooner in the spring and 
cooled sooner in the fall. 
Nest microclimatology: humidities. 
The seasonal changes in soil moisture are similar in the nests of all 
three species (Figure 3). Soil moistures are high in the winter and 
