Antlions, insects resembling feeble, intoxicated dragonflies, flutter briefly in summer, hardly eating, only copulating, reproducing then dying. But their life as larvae is all about food. Living for two to three years at the bottom of a funnel-shaped pit/trap in the ground, the antlion larva waits with open jaws for a smaller insect to fall in, whereupon it paralyzes its prey and sucks out its vital juices.

Now Kazuhiko Matsuda and colleagues at Kinki University in Nara have found that the larvae are in partnership with bacteria that live in the larva's saliva and produce the paralyzing toxin, a protein of a class called chaperonins. The work, published today in Nature, provides an intimate example of symbiosis, where two organisms work in a mutually beneficial partnership, as well as of homology.

Homologues have long provided some of the most persuasive evidence for evolution from common descent. All te- trapods (amphibians, reptiles, birds and mammals) share a pentadactyl (five-digit) limb -- a bat's wing is structurally very similar to a whale's flipper, a frog's foreleg, a bird's wing and a human's hand. There is no reason why this should be, unless all these animals descended from a common ancestor.