Weevils pick on someone their own size

Nature keeps male horned weevils from stupid scraps.

A horned weevil can’t pick a real fight with a male too big for him because the bigger one can’t get a good grip, according to William G. Eberhard of the University of Costa Rica in University City and the Smithsonian Tropical Research Institute and his colleagues. The researchers describe a macho-proof body plan in the June 7 Proceedings of the Royal Society Of London B.

Most male weevils have a pit between the horns leading to a tube, or sheath. When an alluring female inspires a battle between males, combatants stick horns into each other’s sheaths.

To win the fight and the chance to mate, one male must lift the other high enough for the loser’s front legs to scrabble futilely in the air.

By measuring weevil bodies, the researchers found that a big male’s horn won’t fit in a little guy’s sheath. The big male therefore can’t get the right twisting angle to lift his puny rival.

Evolution seems to have delivered a strong message against hopeless fights to at least one species.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.