The Biology of the Lined Shore Crab, 
Pachygrapsus erassipes Randall 
Robert W. Hiatt 1 
INTRODUCTION 
The conspicuous lack of knowledge of the 
natural history of littoral Brachyura (true crabs) 
of the west coast of North America has for a 
long time indicated the necessity for an investi¬ 
gation into the biology of a common and well- 
known decapod, such as the subject of this 
study, Pachygrapsus eras sipes Randall (Frontis¬ 
piece). This investigation has been designed 
to fulfill this need in part and has been pursued 
primarily from the ecologic and behavioristic 
points of view. A considerable portion of this 
paper has been devoted to the description of 
the molt and intermolt cycle of P. crassipes. 
Some recent data which have appeared in the 
literature have dealt with the extremely sig¬ 
nificant molt and intermolt cycles of the can¬ 
croid and oxyrhynchoid crabs, but the grapsoid 
group, to which P. crassipes belongs, has been 
neglected. Therefore, the present study, which 
includes comparable work on this grapsoid crab, 
materially extends the knowledge of these sub¬ 
jects within the group Brachyura. Included here, 
also, is a brief discussion treating the problem 
of the transition in the Brachyura from a 
marine habitat to a semi-terrestrial or amphib¬ 
ious existence. Among littoral Brachyura on 
the northern California coast, P. crassipes ranges 
highest along the shore and exhibits certain 
patterns both physiologically and behavioris- 
tically illustrative of this significant landward 
movement. 
A primary aim has involved recording of 
field observations which have logically pre¬ 
1 Department of Zoology and Entomology, Univer¬ 
sity of Hawaii. Manuscript received October 1, 1947. 
ceded laboratory investigations. Such field ob¬ 
servations have provided the natural basis for 
the present laboratory studies, making the latter 
far more interesting and significant. On the 
other hand, clues to certain behavior patterns 
were exhibited among the captive crabs prior 
to their observation in the natural environment. 
In addition, the correlation of laboratory data 
with field observations has helped to illuminate 
certain behavior patterns, not only of P. cras¬ 
sipes, but of Brachyura in general, which have 
heretofore been incompletely known. It has 
not been the intention of the author to study 
exhaustively the multitude of morphological 
and behavioristic phenomena associated with 
this species. Rather, an attempt was made to 
become better acquainted with the behavior 
of the crab in question, with the underlying 
phenomena involved, and thus with the Brachy¬ 
ura in general. 
Most of the knowledge of the natural history 
of decapod crustaceans stems from a series of 
studies upon those with economic value, 
although for diverse reasons these studies have 
subordinated natural history data in favor of 
securing information on life histories. The early 
literature is filled with abbreviated note-type 
accounts, but the more extensive investigations 
of H. C. Williamson on Cancer pagurus Linne, 
reported at the turn of the century (1899), 
were the first to provide substantial knowledge 
concerning any one decapod crustacean. Shortly 
thereafter Hay (1905) published "The Life 
History of the Blue Crab,” in which he con¬ 
tributed much to the natural history of this 
species. Pearson (1908), in addition to his 
own investigations on C. pagurus, included 
