1981] Mac Kay — Nest Phenologies of Pogonomyrmex 
37 
remain pale for about three weeks. Thus, development from the egg 
through the larval instars requires about three weeks, the pupal 
stage 2 3 weeks, and the callow stage three weeks. 
Most of the eggs are laid in the spring as large amounts are found 
early in the season. The amounts found in later excavations decrease 
and eggs are rarely found after the pupae begin to appear in the nest. 
The larval population reaches a maximum in late July in P. 
montanus, and mid August in P. subnitidus and P. rugosus. The 
pupal population reaches a maximum in mid August in P. 
montanus and late August in P. subnitidus and P. rugosus. The 
callow population reaches a maximum in early to mid September in 
all three species. The callows are easy to distinguish from adult 
workers in P. montanus as they remain pale for at least three weeks 
(based on laboratory observations). The callows of P. rugosus and 
P. subnitidus are much more difficult to distinguish from the adult 
workers. Pogonomyrmex rugosus callows darken to a color indis- 
tinguishable from mature workers within five days. Pogonomyrmex 
subnitidus mature workers are pale making it difficult to distinguish 
them from the callows, even if the callows remain pale for many 
days. 
As the majority of the first individuals produced are sexuals, most 
of the larvae and pupae formed in the first part of the season 
become reproductives. Workers are also produced early in the 
season, especially in P. rugosus. All of the later brood become 
workers as was also found in P. owyheei (Willard and Crowell 
1965). The reproductives remain in the nest only until late August or 
early September. In P. owyheei they remain in the nests until mid 
December (Willard and Crowell 1965). 
The first winged reproductives appear in the nests in late June (P. 
rugosus ) or late July ( P . montanus and P. subnitidus ). The mating 
flights are completed by the first part of September. The highest 
sexual populations occur in mid August. Therefore the colony 
begins production of reproductives early in the year and allows 
them to remain in the nest for extensive periods of time, even 
though they are consuming food. This is true to a lesser extent in P. 
subnitidus, where the reproductives appear in the nest in late July 
and most have left the nest by mid August (Figure 5). 
There are several interesting points in Figs. 4 & 5. Although P. 
rugosus begins production earlier in the year than do the other two 
species, the populations of brood in the nest reach peaks later in the 
