Behaviour of the Soldier Crab — Cameron 
BEHAVIOUR 
Numerous environmental factors such as tide, 
temperature, solar radiation, precipitation, and 
wind are generally considered to influence the 
activities of mobile intertidal animals and of 
shore crabs in particular (Crane, 1958). Soldier 
crabs are usually active for several hours before 
and after low water, although they are more 
active on warm sunny days than in cold over- 
cast conditions. They were observed to be ac- 
tive at night, but their nocturnal behaviour was 
not studied. In daylight hours, cessation of ac- 
tivity and retreat below the surface were fre- 
quently observed in response to apparently 
unfavourable conditions, such as the onset of 
rain. Such periods of retreat ranged from a few 
minutes to the remainder of an intertidal period. 
A pattern of activities is followed by undis- 
turbed populations of M. longicarpus during 
the intertidal period. This pattern will be de- 
scribed as a series of phases of activity, each of 
which merges with the one following but is 
nevertheless generally well defined. Variations 
in the sequence and in the duration of each 
phase occur, and the pattern may be interrupted 
or terminated by unfavourable environmental 
conditions. 
1 . Subterranean Phase 
Activities performed below the surface were 
not studied, but indications of subterranean ac- 
Fig. 1. Adult male M. longicarpus. (Photograph 
by S. Breeden.) 
225 
Fig. 2. Section of an army of M. longicarpus . 
(Photograph by B. Morgan.) 
tivity become obvious some time before the 
crabs make their appearance. On the surface of 
the previously smooth sand small hummocks 
appear and increase in dimensions (Fig. 4). 
These hummocks are always made prior to the 
crabs’ emergence but their formation does not 
necessarily imply that the crabs will emerge. 
Hummock building lasts from 10-30 minutes. 
Just prior to the second phase of activity the 
summits of the hummocks are broken open 
(Fig. 5). 
2. Emergence Phase 
A population may emerge in less than five 
minutes, or the period may be protracted for as 
long as one hour. Generally adults emerge be- 
fore the juveniles. Takahasi’s (1935) statement 
that ”Mictyris never comes out to the surface’" 
is inexplicable. It was ascertained by digging 
that many individuals remain beneath the sur- 
face for an entire intertidal period. Thus, the 
emerged population does not represent the total 
population of the area. Further, the proportion 
of the population which does emerge varies on 
subsequent days. At any locality the emerged 
population may be nearly all adult males on one 
day, and a mixture of all sizes and both sexes 
on the following day. McNeill (1926) thought 
that female M. longicarpus do not congregate 
on the surface to the same extent as do the 
males. This was verified in the present study. 
Upon reaching the surface individuals per- 
form a routine of body care, in which they re- 
move adhering sand grains from the eyes, 
mouthparts, and carapace. They clean the eye- 
