  One of the smallest animals featured in Life, the stalk-eyed fly proved to be a big challenge for crew members to capture on film. As their name suggests, these tiny, unique insects have long stalks projecting from their heads. At the end of each stalk rests an eye. They live in the undergrowth of tropical forests, where they feed on decaying vegetation during the day and, at night, turn their attention to mating. As seen in Life, those stalks play a starring role in the mating process. How exactly does an eye help an animal to win a mate?
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Watch "Stalk-Eyed Flies Inflate Eye Stalks"
Male Stalk-Eyed Flies: From Wide-Eyed to Wide Eyes
A male stalk-eyed fly must feel a lot of pressure. He emerges from his pupal case full of hope and the energy of youth, only to find that he can't enjoy his adolescence. Before his skin hardens, he must transform himself into a mature adult and begin his search for a mate. A suitable partner, however, will remain elusive until he proves himself stronger and fitter than a host of other potential suitors.
To become a female-worthy adult, a male fly must turn his normal eyes into eyes on long stalks. This he accomplishes by swallowing air and then pumping 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.
Life filmmakers were able to document this process in immaculate detail. Watch the scene closely, and you can see the air bubbles in the fly's translucent head. The entire transformation only takes 10 minutes, although the crew had to work much longer than that to obtain enough raw footage to assemble the final scene.
"It took us two weeks to complete the shoot," executive producer Michael Gunton recalls. "Of course, we were only filming for a half-dozen hours over that time. When we finished, we had hundreds of still images of flies at different stages of eye growth."
Growing long eye stalks might seem silly to humans, but it's serious business for these flies. After their stalks solidify, males square off, stand eye-to-eye and assess their "eyespans" against the competition. Males with the biggest eyespans win the available ladies and get to mate with them. Perhaps the females think well-endowed males are stronger and fitter and will result in healthier, more robust offspring.
Even if that's not technically true, it doesn't matter. Males with these longer appendages mate more frequently than shorter-stalked rivals, ensuring that their genes — and their traits — are passed to the next generation.
Continue: A Filmmaker's Dilemma: Fly by Night
