44 
Psyche 
[Vol. 88 
area containing P. montanus, but the lower levels of the nest may 
also become flooded when the snow melts. Many of the larvae and 
pupae are found in the upper levels of the nest, but there is 
apparently a downward movement of the brood and callows in 
October and November. By December there is no brood in the nest. 
Most of the reproductives are found in the upper 30 cm of the nest 
(Fig. 7). 
The seasonal movements in P. rugosus nests are similar to the 
other two species (Figure 8). Most of the worker population is in the 
upper levels of the nest throughout the spring and summer. In 
September and October until December, the ants become distri- 
buted throughout the nest. The larvae are dispersed throughout the 
nest during most of the year, but appear to be moved into the deeper 
levels of the nest at the beginning of the winter. The pupae are 
located in the upper levels of the nest but also appear to be moved 
into the deeper regions of the nest in the fall. The callows also 
demonstrate a movement into the deeper nest levels in the fall. 
Again, it is difficult to make inferences concerning the sexuals as 
they are in the nest for a short period of time, but both sexes appear 
to be in the upper levels. 
In the winter the ants seem to be dispersed throughout the nest 
and do not avoid the lowest levels of the nest. There is no winter 
snow at Riverside and the temperatures are higher than those in the 
mountains (Figure 1), therefore the ants remain somewhat active 
throughout the year. 
The seasonal patterns of distribution within the nests are similar 
in all three species. The reproductives (when present) and workers 
are most abundant in the upper levels of the nest, except in the 
winter. The brood are in the deeper levels where the microclimate 
undergoes little change. The callows are in the lower levels of the 
nests in all three species and apparently care for the brood. This is 
common in ants in general (Wilson 1971) and in P. badius (Gentry 
1974). No callows were ever seen foraging. They do not quickly 
darken on exposure to sunlight. 
It is commonly stated that ants keep the larvae and pupae 
separate within the nest to take advantage of the optimal conditions 
for the development of each (Wheeler 1910; Protomastro 1973). In 
Pogonomyrmex, at least P. marcusi is reported to practice such 
behavior (Marcus and Marcus 1951). I have no evidence that the 
