The Solomon Islands and Their Natives

by H. B. Guppy

I kept the crab alive on board on a diet of cocoa-nuts for three weeks, when, one morning, to my great disappointment, I found it dead. Other foods, such as bananas, were offered to it but were left untouched, and its appetite for cocoa-nuts continued unimpaired to the last day of its life. Being desirous of observing the manner in which the husk was removed, I had a cocoa-nut with its husk placed in the coop in which the crab was kept. On one occasion the Birgus was surprised with the nut between its large claws; but, notwithstanding that no other food was offered to it for a day and a half, it did not attempt to strip off the husk. So the operation was done for it, and a small hole was knocked in the top of the shell. On the following day I found the shell—a young and somewhat thin one—broken irregularly across the middle, with the soft white kernel already removed and eaten. It was afterwards found necessary to break the nuts for its daily food.

In 1884, when the “Lark” was in Bougainville Straits, three of these crabs were kept on board with the intention of taking them down to Sydney. Mr. W. Isabell, leading-stoker of the ship, looked well after them, as he had also done in the case of the previous crab, but within three or four weeks they had all died. The cocoa-nuts had to be husked and broken for them, as they were in vain tempted to do it for themselves. One crab, however, was frequently observed clasping between its claws a full-grown unhusked nut, the upper end of which showed deep grooves and dents from the blows of its claws; and Mr. Isabell and I came to the conclusion that the coop, in which these crabs were placed, was too low to allow of the free play of the great claws.

My evidence alone would be sufficient to convict the Birgus of this offence: for an offender it would certainly be in the eyes of the owner of a plantation of cocoa-nut palms. I learned from Mr. Isabell that the first crab we had on board consumed, on the average, two cocoa-nuts in three days. A number of these crabs in a cocoa-nut plantation, might therefore prove a considerable pest: for, if this betokens the quantity of food which the Birgus consumes in a state of nature, a single crab in the course of twelve months would dispose of about 250 cocoa-nuts, which represent the annual production of three palms and between 20 and 30 quarts of oil.

As these crabs disliked observation, I was unable to gain much knowledge of their habits by watching. During the day-time they were sluggish, did not eat, and kept themselves in the further corner of the coop, as far from the light as possible. At night they moved about very actively and fed vigorously on the cocoa-nuts. The natives of the Shortlands, who were well-acquainted with the cocoa-nut eating habit of the Birgus, described to me the mode of husking and breaking the nut, just as Mr. Liesk described it to Mr. Darwin. They esteem as an especial luxury the fat which gives the chief bulk to the abdomen of the crab.

The habit of the Birgus, when surprised away from its burrow, is not to turn round and run away, but to retreat in an orderly manner with its front to the foe. Having reached some root or trunk of a tree which protects in the rear its less perfectly armoured abdomen, it makes a regular stand, waves one of the long second pair of claws in the air, and courageously awaits the attack. The attitude of defence is worthy of remark. The two large claws are held up close together to defend the mouth and eyes, but with the pincers pointing downward—the posture reminding me of the guard for the head and face in sword-exercise. One of the long second pair of claws is planted firmly on the ground to give the crab additional support; whilst the other claw is raised in the air and moved up and down in a sparring fashion. The whole attitude of the Birgus, when on the defensive, is one of dogged and determined resistance. The big pincers that point downward are ready to seize anything which touches the unprotected under surface of the abdomen; but on account of the position of these claws in front of the eyes, it can only foresee attacks from above, and it therefore cannot ward off a sudden thrust directed against the abdomen, although it may afterwards inflict severe injuries on the aggressor.

There seems to be some doubt whether the Birgus ascends the tree to get the cocoa-nuts or whether it contents itself with those that have fallen. Almost every author who refers to this crab alludes to its climbing the tree, and it is also said to climb the pandanus. The testimony in support of its climbing powers is almost conclusive, yet Mr. Darwin was informed by Mr. Liesk that in Keeling Atoll the Birgus lives only on the fallen cocoa-nuts, and Mr. H. O. Forbes,[456] who has recently visited this island, confirms this statement.

[456] “A Naturalist’s Wanderings,” etc.: London, 1885, p. 27.

My readers, after perusing the foregoing remarks, will agree with me that from the lack of actual observation on the part of the authors, who describe the cocoa-nut eating habit of this crab, there has been fair grounds for scepticism. Even now, we are but imperfectly acquainted with the mode of life of the Birgus, which is a subject I would commend to the attention of residents in the Indian and Pacific Oceans.

I may add that the Birgus is partial to other kinds of fruits beside cocoa-nuts. Different writers mention candle-nuts, nutmegs, figs, and other rich and oily nuts and fruits. In some islands it would seem that the Pandanus fruit is its only diet; and for breaking open these tough fruits, its heavy claws are well adapted, though from personal experience, I should remark that the crab would have its strength and ingenuity taxed almost as much as in the case of the cocoa-nut.