STALK-EYED FLYFeatured in the "Challenges of Life" episode of Life.
 More LifeIn the lush undergrowth of the world's tropical forests, a war is waged nightly. You won't see it, though, unless you squat close to the ground and peer at the decaying vegetation with a hand lens. There, you might witness a swarm of small, blackish flies battling for their little piece of the salad bar. Look more closely, and you'll see that the flies have long stalks projecting from their heads. At the end of each stalk rests an eye.
Scientists refer to these strange-looking insects as stalk-eyed flies and classify them into the family Diopsidae. Members of the genus Diopsis are probably the best-studied, and it's in these flies that the stalk-eyed adaptation gets pushed to the limit.
MY, WHAT BIG EYES YOU HAVE
Stalk-eyed flies aren't born with their high-rise eyes. It's only after the animal emerges from its pupal case, or protective covering, that the transformation begins. This is how it works: Before its skin hardens, a fly swallows air and then pumps it into a small cavity behind the eye. As pressure builds up, the cavity expands and unrolls to form the long stalks characteristic of the adult. When the fly's skin hardens, the eye stalks become fixed in place, like rigid sticks. Both males and females have eye stalks, but they are much longer in males.
EYEING THE COMPETITION
Their unique eyes may offer certain advantages. But the most important function of the eye stalks is wooing female flies. Every evening, the females climb from low vegetation to higher rootlets and leaves. They gather in tight clusters and, just like girls at a high-school dance, wait for the boys to come calling. When the male flies arrive, they begin sparring, not by punching or biting, but by comparing their relative sizes. The males rear up on their hind legs and, literally, go eye-to-eye. After a quick assessment, the male with shorter eye stalks slinks away, defeated. The winner gets everything — the territory and the cluster of females that come with it. He also earns the right to mate with the females and to transmit his genes to another generation.
Written by William Harris, HowStuffWorks
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