62 
Psyche 
[June 
considerable number of these old plants and examined the 
soil beneath them. In no case did I find a nest of ulcerosus. 
But in fully half the cases the plant surmounted a flourish- 
ing colony of Pheidole vaslitti arizonica. 
By this time I was convinced that ulcerosus does not 
usually found its nests beneath agave plants but as to where 
to look for them I had no idea. Then, largely through luck, 
I stumbled on five colonies. Three of these were situated 
in open areas on the agave slope but at some distance from 
the nearest agave plant. The other two were placed at the 
edge of oak thickets on the opposite side of the ridge. In 
every case the nest was situated on a slope that faced south- 
east . I was able to excavate three of these nests completely. 
I might have done so with the other two had I not lost con- 
tact with the passages through over-hasty excavation. Each 
nest consisted of a rather obscure entrance between stones 
which were embedded in the soil. In two cases there was a 
thin disc of excavated soil spread around the entrance but 
this was not present in the other nests. From the entrance 
a single, tortuous passage twisted through the soil between 
and under stones at a depth which was seldom more than 
six inches below the surface. At intervals, usually beneath 
the lower surface of a stone, the passage widened into a 
small, irregular chamber. In each of these were major, me- 
dia and minor workers and some brood. The queen was 
usually taken in the last chamber at the inner end of the 
nest. As there was no telling which direction the passage 
would take, the soil had to be removed a bit at a time to 
avoid losing the passage altogether. However, the absence 
of any lateral passages considerably simplified matters. Be- 
cause the excavation had to be made slowly, there was 
ample opportunity to secure foraging workers as they re- 
turned to the nest. I believe, therefore, that the figures for 
the three colonies given below represent most of the popula- 
tion in each case. In the first colony there were one hun- 
Explanation of Plate 5 
Camponotus ( Myrmaphaenus ) ulcerosus Wheeler, Fig. 1. Ulcerate 
major worker. Fig. 2. Media worker. Fig. 3. Minor worker. Fig. 4. 
Female. Fig. 5. Non-ulcerate major worker. All figures to the same scale. 
