182 
Psyche 
[June 
Figure 1 . Frequency distribution of forager head width. The solid line is of 154 
foragers with dark thoraxes; the dotted line is of 126 foragers with red thoraxes. The 
population appears to be dimorphic for both color and size. 
of size classes. These are shown in Figure 1. A total of 280 indi- 
viduals are represented, with 154 dark and 126 red. Mean head 
width of the dark forms is 0.944 ± 0.067; of the red forms, 1.111 ± 
0.065 mm. A t-test of the two means indicates the differences are 
highly significant (p < 0.005); the population is dimorphic for 
both color and size. 
The mean head width for each sample of 20 individuals was 
calculated and tested for degree of correlation with foraging height 
at which the sample was collected and time of day. No significant 
correlations were found to exist between foraging height and head 
width. There was, however, a significant positive correlation be- 
tween mean head width and the time of day that the sample was 
collected. This relationship is shown in Figure 2. The correlation 
coefficient, 0.848, is significant at p < 0.005. 
