Biology of Pachygrapsus crassipes —HIATT 
179 
tween widely separated populations. A single 
record of a most interesting behavior pattern 
was taken during observations on crabs in a 
tide pool at Moss Beach, California. The fol¬ 
lowing excerpt from my field notes serves to 
describe this activity. 
A large male walked slowly by a black turban 
(Tegula funebralis) in a forward direction; it 
stopped beside the turban, quickly side-stepped 
laterally and grasped the shell, overturned it, 
and seized the turban behind the operculum 
with a cheliped before it could withdraw. The 
crab held the turban for several minutes, making 
repeated attempts to pull it from its shell. After 
attempts to extricate the animal met with fail¬ 
ure, the free cheliped was employed to tear the 
flesh behind the operculum. A few seconds 
later the crab repeated its stalking behavior on 
a hermit crab in a black turban shell, but the 
hermit crab withdrew before the crab could 
grasp it. The opercular function of the hermit 
crabs large cheliped was dynamically illustrated. 
Observations made along the Monterey coast 
disclosed repeated attempts by P. crassipes to 
crush the shells of the littorines which are 
present in vast numbers in the high-tide pools. 
All attempts met with failure. Recently molted, 
partially devoured H. nudus were found in two 
tide pools at Monterey. Circumstantial evidence 
seemed to incriminate P. crassipes inasmuch as it 
was the predominant inhabitant of the pools, 
particularly since it is known that it is canni¬ 
balistic on recently molted individuals. 
Indisputable records of cannibalistic behavior 
in this species—17 in the laboratory and 3 in 
the field—were secured. The soft parts of the 
body are eaten; the pereiopods and branchial 
chambers are undisturbed. Without exception, 
the ravaged individuals were recently molted 
animals, no later than stage A x . Recently molted 
animals in the laboratory aquaria were invaria¬ 
bly victims, if hard crabs were present in the 
same aquarium. It was early discovered that 
molt and intermolt data had to be secured from 
isolated individuals in the laboratory. The lack 
of more frequent records of cannibalism is un¬ 
doubtedly correlated with nocturnal ecdysis and 
the rocky habitats with abundant refuges to 
which the crabs retire immediately after exu¬ 
viation. 
Stomach analyses were made on 50 specimens 
of this species collected early in the morning. 
The crabs were preserved in 10 per cent formalin 
and examined shortly thereafter. The major 
constituents detected in order of decreasing 
quantity were as follows: algal tissues, diatoms, 
and striated muscle fragments. The latter item 
was found in 17 stomachs; several partially 
devoured sardines left adjacent to the pool by 
fishermen were undoubtedly the source. Had 
the fish been absent, it is doubtful that any 
animal food would have been found in the 
stomachs. These data serve to substantiate the 
field observations presented above. Pearse 
(1931) cites food consumption figures of 51 
per cent flesh and 49 per cent plant material 
for P. crassipes in Japan. If these data are 
normal, the food habits of the Japanese repre¬ 
sentatives differ widely from those on the Amer¬ 
ican coast. 
P. crassipes along the central California coast 
may be designated as essentially an herbivore, 
ordinarily a grazing herbivore, less commonly a 
plant scavenger, while facultatively a carnivore, 
chiefly an animal scavenger, and less frequently 
a predator. An organism subscribing to such 
generalized food habits can easily withstand 
periodic deficiencies in one or more food 
sources; this, coupled with the fact that the 
high littoral zone offers an uncontested food 
supply, has been a major factor underlying the 
success of this species. 
Use of the Chelipeds 
The chelae are perhaps the most important 
and useful appendages of P. crassipes, and as 
such merit special consideration here. The sev¬ 
eral podomeres articulate at varying angles, 
enabling the crab to describe an extensive arc 
about itself. Sexual dimorphism with respect 
to the chelae is negligible, those of the male 
being only slightly larger. Although very few 
of the normal activities of this crab are ordina¬ 
rily undertaken without the use of the chelae, 
several crabs which had autotomized the chelae 
