The Fly With 100 Eyes

By LEON JAROFF

For all their brief lives, the females of one species of twisted-wing insects called Xenos peckii live inside common paper wasps, feeding on their hosts' innards. Sightless and flightless, these tiny parasites exist only to be impregnated. The luckier males mature inside the wasps, emerge at adulthood and fly away, using their olfactory sense and their eyes to find and mate with a female inside another wasp.

But, oh, what eyes! Peering through a microscope at a twisted-wing male, Cornell neurobiologists Elke Buschbeck, Birgit Ehmer and Ron Hoy were struck by the unusually large lens facets in X. peckii's eyes. The compound eyes of most insects have hundreds of much smaller facets. Each focuses on a handful of photo receptors and produces only a single point in the insect's visual field. But the researchers, reporting last week in the journal Science, found that each of X. peckii's 100 eyelets is really a complete eye with its own retina, consisting of some 100 receptors, that samples a "chunk" of the visual field. These neighboring chunks, when combined in the insect's brain, produce an image with exceptionally high resolution.

While this clever visual mechanism seems unique among contemporary creatures, a similar one existed in another, more ancient species: the segmented trilobites, which became extinct 230 million years ago.

X. peckii needs excellent vision in order to prevent its own extinction. "Sex pheromones from females probably help males locate the general neighborhood of a wasp," says Ehmer. But the male, who lives less than 6 hrs. after taking flight, must rely on his eyesight to zero in quickly on that wasp and its female parasite so he can perpetuate his species before he expires.