The Malay archipelago : the land of the orang-utan ... - Wallace Online

sxxii.] ARU ISLANDS.—SECOND RESIDENCE AT DOBBO. 365well, and could resume my daily walks in the forest. I did not,however, find it so productive as when I had first arrived atDobbo. There was a damp stagnation about the paths, andinsects were very scarce. In some of my best collecting placesI now found a mass of rotting wood, mingled with young slioots,and overgrown with climbers, yet I always managed to addsomething daily to my extensive collections. I one day metwith a curious example of failure of instinct, which, by showingit to be fallible, renders it very doubtful whether it is anythingmore than hereditary habit, dependent on delicate modificationsof sensation. Some sailors cut down a good-sized tree, and, as isalways my practice, I visited it daily for some time in search ofinsects. Among other beetles came swarms of the little cylindricalwood-borers (Platypus, Tesserocerus, &c.), and commencedmaking holes in the bark. After a day or two I was surprisedto find hundreds of them sticking in the holes they had iDored,and on examination discovered that the milky sajD of the treewas of tlie nature of gutta-jDercha, hardening rapidly on exposureto the air, and gluing the little animals in self-duggraves. The habit of boring holes in trees in wliich to deposittheir eggs was not accompanied by a sufiicient instinctiveknowledge of which trees were suitable, and whicli destructiveto them. If, as is very probable, these trees have an attractiveodour to certain species of borers, it might very likely lead totheir becoming extinct ; while other species to whom the sameodour was disagreeable, and who therefore a\oided the dangeroustrees, would survive, and would be credited by us withan instinct, whereas they would really be guided bj^ a simplesensation.Those curious little beetles, the Brenthidse, were very abundantin Aru. The females have a jDointed rostrum, with whichthey bore deep holes in the bark of dead trees, often buryingthe rostrum up totlie eyes, and in these holes deposit their eggs.The males are larger, and have the rostrum dilated at tiie end,and sometimes terminating in a good-sized pair of jaws. I oncesaw two males fighting together ; each had a foi-e-leg laid acrossthe neck of the other, and the rostrum bent quite in an attitudeof defiance, and looking most ridiculous. Another time, twowere figliting for a female, who stood close by busy at herboring. They pushed at eacli other with their rostra, and clawedand thumped, apparently in the greatest rage, although theircoats of mail must have saved both from injury. The small one,however, soon ran away, acknowledging himself vanquished,In most Coleoptera the female is larger than the male, and it istherefore interesting, as bearing on the question of sexualselection, that in this case, as in the stag-beetles where themales fight togetlier, they should be not only better armed, butalso much larger than the females.Just as we were going away, a handsome tree, allied toErythrina, was in blossom, showing its masses of large crimson