Behaviour of the Soldier Crab — Cameron 
229 
tion. Furthermore, the faeces of the animals are 
devoid of sand grains. 
In discussing the feeding mechanism of Uca, 
Miller (1961) remarks that "the thoroughness 
with which the crabs are able to sort food ma- 
terial from the mineral fraction of the sub- 
stratum corresponds to the availability of the 
food material." He showed that the sandy beach- 
inhabiting U. pugilator ingests a minimal 
amount of sand, whereas for the marsh-inhabit- 
ing U. pugnax "food is more readily available 
because the silt with which it is generally as- 
sociated is of sufficiently fine texture to be in- 
gested.” Furthermore, in those ocypodid crabs 
which possess them, the spoon-tipped setae of 
the mouthparts are present in greater numbers 
and exhibit more elaborate spooning in species 
inhabiting sandy substrata than in species of 
muddy environments (Crane, 1941, 1943; Al- 
tevogt, 1957; Miller, 1961). Mictyris longicar- 
pus possesses large numbers of densely packed 
spooned setae. They are present on the inner 
surface of the third maxillipeds, the outer and 
inner surfaces of the second maxillipeds, the 
basipodite of the first maxillipeds, and the outer 
surface of the endite of the coxopodite of 
the first maxillipeds. There are four types of 
spooned seta, which are shown in Figure 7. 
6. Army Wandering Phase 
Soldier crab armies present a spectacular 
sight. They may cover vast areas of the beach 
and their tightly packed masses create a rustling 
noise audible at a considerable distance. The 
army wandering phase begins with the cessation 
of feeding. Sometimes the transition is sudden 
but usually it is gradual. Armies are generally 
composed of similarly sized individuals, usually 
adult males. Only rarely do females wander in 
armies, though mixed armies occur. In mixed 
armies, the largest crabs progress in the van- 
guard, probably because they walk faster than 
do the smaller ones. In no sense does any section 
of an aggregation lead the rest. The advancing 
front changes continuously, and the crabs often 
walk over each other, two and three deep, in the 
general scramble. Crowding may be even worse 
than this, especially when the advancing front 
reaches standing water and stops. Armies cover 
great distances during this phase. They com- 
monly walk as far as 500 yards, the rate of 
progression being about 10 yards per minute. 
Army wandering occupies from 30 minutes to 
2 hr. When emerged females are present but 
have not joined armies, their feeding activities 
Fig. 6. Feeding pellets deposited by soldier crabs. (The ruler is 15 inches long.) 
