48 
Psyche 
[Vol. 88 
Gentry 1964; Gentry 1974). MacKay (1981) presents data on the 
respiratory rates and fat contents of workers taken from the 
different levels of the nests of the three species. In winter, spring, 
and fall, there are significant differences between the levels with 
regard to both of these parameters. If mixing of the workers did 
occur between the different levels of the nest, we would not have 
found these consistent differences between workers taken from 
different levels. 
There is little evidence of seasonal movements of the nest queens 
(Figure 9). In the spring P. occidental is queens ascend into the 
upper levels from the lower levels (Lavigne 1969). The queens may 
be moved into the deeper regions during the winter for greater 
protection. In the spring, the soil begins to warm sooner in the 
superficial levels. The queen may be moved to the higher warmer 
levels in order to increase her metabolism for initiation of egg 
production. 
Guests. 
Many species of insects and spiders were collected within the ant 
nests. The occurrence of most of these species is probably accidental 
and individuals of most species were found only in small numbers 
(one or two individuals per nest). Those species most commonly 
found include: Orthoptera — Myrmecophila manni Schimmer, in the 
nests of all three species; Coleoptera — Echinocoleus setiger Horn, in 
P. montanus and P. subnitidus nests, Hetarius hirsutus Martin and 
H. sp.#l with P. montanus, H. morsus Leconte and H. sp.#2 with P. 
subnitidus, Cremastocheilus westwoodi Horn in the nests of P. 
subnitidus. There are at least two species of unidentified staphylin- 
ids that are common in P. subnitidus nests (more than 10 per nest). 
Hymenoptera — Solenopsis molesta (Say) is common in P. mon- 
tanus and P. subnitidus nests, Pheidole spp. in P. rugosus nests. Of 
the three harvester ant species, P. subnitidus has the greatest 
number of guests and diversity of species. 
Food input into nests. 
All three species demonstrate similar seasonal changes in their 
foraging patterns, with much activity in mid-summer and no activity 
in the winter and early spring (Figures 10 and 11). There are 
important differences between the three species. Foraging in P. 
rugosus begins earlier in the spring and extends later into the fall 
than in the other two species. Pogonomyrmex subnitidus has an 
