1981] MacKay — Nest Phenologies of Pogonomyrmex 
57 
is similar in both species. Pogonomyrmex rugosus brings in more 
bird feces than mammal feces, P. montanus and P. subnitidus bring 
in more mammal feces than bird feces. A distinction was made 
between “hard” insects and “soft” insects. Hard insects included 
those heavily chitinized forms, especially the Coleoptera and certain 
Formicidae. Soft insects included Homoptera, most Hemiptera, 
most Diptera, larvae and pupae of most orders and a few non- 
insects such as spiders. It appears that the degree of chitinization 
may not be important as the proportions of hard and soft insects 
were similar. All three species have chitinase activity in their gasters 
(MacKay, unpub. data). 
Plant parts consist of pieces of leaves and flowers and in the case 
of P. montanus, pine resin. Flowers of Penstemon spp. and 
Arctostaphylos spp. are transported to the nest and placed around 
the brood, possibly to increase the humidity. Later the intact flowers 
are discarded at the nest surface. This indicates the flowers are not 
placed around the brood to protect them from predators. In the case 
of pieces of leaves, apparently they are eaten by the ants as they do 
not later appear on the nest surface. There is considerable seasonal 
change in the food composition of P. montanus and P. subnitidus 
(Figure 13). The percentages of insects brought into P. montanus 
nests changes little seasonally. There is a seasonal reduction in the 
percentage of utilization of insects in P. subnitidus. There is little 
seasonal change in the proportion of the food sources composed of 
feces in the two species, although a slight reduction may occur. In 
both species, especially P. montanus, there is a seasonal decrease in 
the proportion of plant parts brought to the nest. In both species, 
there is a dramatic increase in the utilization of seeds after July. This 
increase is probably related to a greater availability of seeds after the 
flowering period of annual plants. A similar comparison was not 
made in the case of P. rugosus as non-seed materials are a very small 
portion of their diet (Fig. 12). In P. rugosus, there was a seasonal 
drop in the proportion of the diet composed of Erodium eicutarium 
(L.) L’Her. seeds (May 90.3%, June 91.0%, July 88.9%, August 
89.7%, September 84.1%, and October 80.9%). Other seeds, espe- 
cially those of Pectocarya linearis DC and Festuca octoflora Walt., 
made up most of the difference. 
Caloric analysis of the food entering the nests of the three species 
indicates that a P. montanus colony receives an average of 166.6 
