1953] 
Creighton — Camponotus ulcerosus 
88 
from the aperture. In this respect it behaves essentially as 
does the major of Colobopsis. There are, however, a number 
of interesting differences in the process. When the head 
of the major of Colobopsis is serving in its phragmotic 
capacity, the only portions of it presented to the exterior 
are the jaws and the truncated anterior face. The antennae 
are folded back against the sides of the head and they are 
well removed from the exterior : it is difficult to see how they 
could receive tactile stimuli. This may be why Wheeler 
(Bull. Amer. Mus. Nat. Hist., Vol. 20, No. 10, p. 154, 1904) 
was unable to elicit any response when he attempted to 
cause the withdrawal of the Colobopsis major by touching 
the exposed portion of the head with a pin or straw. The 
head of the major of ulcerosus, when in the phragmotic 
position, can readily receive tactile stimuli with the an- 
tennae. For these parts are not concealed, but held so that 
each funiculus lies at one side of the aperture. The return- 
ing workers touch the exposed antennae of the occluding 
major with their own antennae to secure entry for, when 
thus stimulated, the major withdraws its head from the 
aperture. This same response can be elicited by touching 
the antennae of the occluding major with a bit of grass. 
The major of ulcerosus is capable of a rather surprising 
range of behavior when acting as a guard. As a general 
rule a strange ant can walk across the face of the ulcerosus 
major, when the latter has assumed the phragmotic position, 
without producing any visible response. Occasionally, how- 
ever, the major will seize the strange ant in its jaws and 
jerk it into the nest, where it is, presumably, killed. Further- 
more, the major of ulcerosus does not always take a position 
where its head blocks the entrance. During periods when 
little traffic is passing the “door”, the major on guard often 
remains well inside the carton, with only the tips of the 
antennae showing at the aperture. From this position it can 
pop into place instantaneously, which it does if a strange 
ant walks onto the shield. If foraging has ceased and there 
are no strange ants in the vicinity, the major may retreat 
so far from the aperture that it cannot be seen when a beam 
of light is thrown through that opening. It is of interest 
to note that the major of ulcerosus is not limited to serving 
