Research Items

Abstract

Secondary Sexual Characters in Beetles THE great development of horn-like outgrowths in male Dynastid beetles is a conspicuous secondary sexual character. What these horns are used for has long attracted attention and excited speculation. William Beebe (Zoologica, 29, Aug. 1944) records observations made in the New York Zoological Society's Laboratory at Caripito, Venezuela, on the elephant beetles Megaeoma elephas and Strategus aloeus. In both these species he finds that the males use their cephalic and thoracic horns for fighting with each other. The initial stimulus appears to be the advent of the rainy season. The technique of fighting seems to be the same for both species: first an effort to unbalance the opponent by tripping, and then by ventral attack with the anterior horn so as to throw him on his back. It is interesting to note that Charles Darwin, in the first edition of "The Descent of Man", claimed that the most obvious conjecture is that these horns are used by the males for fighting together. But since they had never been observed to fight, he came to the conclusion that they were acquired as ornaments. Eight years afterwards, A. R. Wallace, in "Tropical Nature", expressed the view that these horns may be protective. Their presence, he says, would render it very difficult for the large-mouthed goatsuckers and other nocturnal birds to swallow the beetles. It is therefore noteworthy that Mr. Beebe's observations appear to settle this disputed point, and are supported by a very convincing series of successive photographs taken of actual combats.