40 
Psyche 
[Vol. 88 
other males (See Figure 2 of Holldobler 1976b and Figure 4 of 
Markl et al. 1977). Prior to the mating flight, male respiratory rates 
doubled or tripled (MacKay 1981). The individuals with higher 
activity levels may be able to increase their fitness by excluding 
other males from a female or by capturing a female quickly and 
moving into the copulatory position before other males arrive. 
After the female has copulated for a short time, she bites the 
gaster of the male which is copulating with her. He usually 
relinquishes his position to another male. There is considerable 
fighting and tumbling so it is difficult to determine the numbers of 
times a female mates. Observations suggest that a single female 
mates at least 3 or 4 times. She may have mated previously with one 
or more of her brothers in the nest. I observed one mating within the 
nest of a laboratory colony of P. montanus. In all three species, the 
males attempt to mate with their sisters during emergence from the 
nest, although a complete copulation was never observed. 
After several copulations the females leave the mating swarm 
either by flying or walking away. The males no longer show interest 
in such females, as the females apparently stop releasing a phero- 
mone (Holldobler 1976b). Most females then fly away from the 
area. A few remain and within a few minutes begin excavating nests 
near the mating site. As the density of such nests is very high (more 
than 4 per square meter) the success rate is undoubtedly low. 
Several times I saw females near the mating area attempt to “steal” 
the excavation hole of another female, but were chased away by the 
resident female. Such attempts are common and are occasionally 
successful (Markl et al. 1977). 
Seasonal changes in the positions of inhabitants within the nests. 
The seasonal movements in the positions of the inhabitants of the 
nests depicted in Figures 6, 7 and 8 are similar to those described in 
P. owyheei (Willard and Crowell 1965) and P. occidentalis (Lavigne 
1969). The depths are not comparable between the three species as 
the nests of P. rugosus are deeper than those of P. subnitidus which 
are in turn deeper than those of P. montanus (Appendix 1). In most 
cases the time axis is expressed in months of the year with the 
exception of the sexuals in which only four months are shown. In all 
cases, the proportions represent means of all nests excavated. 
Most of the nest population of P. montanus, including the 
