ON THE ROBBER CRAB (bIRGUS LATRO). [DeC. 14, 



its habits described by numerous obsei'vers, there is still con- 

 siderable doubt and difterence of opinion concerning it. This 

 uncertainty^ probably arises from two causes — first, that the habits 

 of this animal do actually differ considerably in different localities, 

 and, second, that the unreliable reports of .natives have often been 

 accepted as authentic. The chief point on which observers differ 

 is wliether this Crustacean can or cannot climb ti'ees : thus Chun 

 (Aus den Tiefen des Weltmeeres (1900), p. 414) states that the 

 natives of Diego Garcia say they never have seen it do so, but 

 since on the same authority, it is stated that these crabs carry 

 coconut shells of sea-water with them into the woods, it does not 

 .seem necessary to attach much impoitance to their tales. On the 

 other hand, most observers agree that Birgu.s can and does climb 

 palm trees, and that this statement is correct is proved by the 

 photograph taken by me in Christmas Island, showing two crabs 

 actually on the trunk of the native Sago-pahn (Arenga listeri) : 

 the upper one is ascending and the lower descending. Numerous 

 other individuals are seen round the foot of the tree, taking 

 advantage of the fruit dropped by their more enterprising com- 

 panions which have ascended in search of it. 



In climbing, the large claws are scarcely used at all, the animal 

 clinging to the tree trunk by the sharp points of the walking- 

 legs ; by the same means neaily vei-tical faces of rock, where there 

 is apparently little foothold, can be ascended and descended. 



Although there is no doubt that these crabs can and do feed on 

 coconuts when they can get them, these are by no means their 

 only food as would seem to be implied by some accounts. In 

 Christmas Island during my first visit (1897-8) there were no 

 bearing coconut palms so far as I was aware, and though there 

 may have been a few on one small beach on the east coast, these 

 could only have supplied food for a few individuals. The ordinary 

 food included fruits of various kinds, particularly those of the 

 Sago-palm (A)'enga listeri) and of the Screw-pines (Fandamcs), 

 and carrion of all sorts, even the bodies of their own relations. 

 Their discrimination is not very keen, for they will drag away 

 almost anything that has been handled, such as cooking utensils, 

 bottles, geological hammers, and clothes. In one case I had a 

 geological hammer practically ruined by having its handle 

 splintered in the powerful claws of one of these creatures. 



It is usually stated that Birgus is noctunial in its habits, and 

 probably this is usually the case, but in Christmas Island they 

 move about the forest and feed even in the brightest daylight (as 

 is shown by the photograph). Formerly, when the native rats 

 swarmed in the forest after dark, the crabs moved about com- 

 paratively little at night, and might often be seen clinging to the 

 trunk of a tree two or three feet from the ground. Now, the rats 

 having become extinct, the crabs wander about at night and are 

 a great nuisance, dragging from the camp anything they can get 

 hold of that seems edible. On one occasion I saw a large in- 

 dividual carrying off a coconut from which the husk had been 



