Too clever by half

Natural History, Feb, 2006 by Nick W. Atkinson

Many harmless, tasty animals mimic others that are dangerous or poisonous--an evolutionary tactic that affords protection from predators without the metabolic costs of the real threat. Jumping spiders of the genus Myrrnarachne, for instance, bear a striking resemblance to ants, whose powerful mandibles and stings many predators avoid. More precisely, the adult female and juvenile spiders look like ants; but for the adult males, things are more complicated.

Intense sexual selection--competition between males to mate--has led male jumping spiders to evolve greatly elongated mouthparts. Those mouthparts, which make the male spider look as if it is carrying a large object such as prey, are enticing to female spiders. But such "compound mimicry" has a downside, according to research done at the University of Canterbury in New Zealand by behavioral ecologists Ximena J. Nelson and Robert R. Jackson. Predators that avoid ants are still deterred by the ant mimicry. But predators that specialize in eating ants know that the best time to attack is when the ants' pincers are clamped on something else. Bye-bye, spider! (Proceedings of the Royal Society B, forthcoming)