for National Geographic News
Human engineers strive to create airplane wings matching in shape and size, and for good reason. When wings are mis-matched in nature, flight—if possible at all—can be dangerously unpredictable.
That's why scientists were shocked to spot an insect with wings that seem to defy the forces of nature. One tiny predatory fly, new to science and discovered in Arizona, has left and right wings that are consistently different in shape and size, or asymmetrical. The size discrepancy, alone, is six percent or more.
According to bug scientists behind the find, this is the greatest degree of wing asymmetry yet seen in any insect, bird, or other flying animal. The oddly-paired wings, seen only in males of the new species Erebomyia exalloptera, might be an unusual type of ornament for wooing females, researchers wrote in the science journal Biology Letters.
"Six percent is a pretty significant difference," said entomologist and study author Justin Runyon. "At first we thought maybe they wouldn't be able to fly at all, or that they might fly in circles."
Flying in Circles
Though a few other insects, including a species of butterfly and a damselfly, have been shown statistically to have minute differences in wing size before, the variances have been too miniscule for the human eye to detect.
Runyon, a doctoral student presently at Pennsylvania State University, and supervisor Richard Hurley of Montana State University, first discovered the animal on a field trip to Arizona in 2001. The pair were collecting flies of the family Dolichopodidae, all long-legged carnivorous species that feast on other insects. "They use their [powerful] mouth parts to suck the juice out of little bugs," said Runyon.
Runyon spotted a dolichopodid he didn't recognize and later analysis in the lab suggested that the unknown flier had wings that didn't match up. "I thought it was just a malformed individual, but then I found another, and another," said Runyon. A subsequent trip to the same Arizona sites in spring 2003 revealed more of the same odd-winged Erebomyia. This time the researchers observed the animal airborne, proving that the wings are functional.
Runyon and Hurley considered that environmental contamination could explain the deformity, but they found the same mis-matched wings on flies at two locations hundreds of miles apart. In addition, both sites appear to be pristine and pollution free.
Communication on the Wing
During their 2003 field trip, however, the scientists noted an unusual mating behavior that might explain how such a potentially harmful physical characteristic like asymmetrical wings is able to persist in the fly. Typically, damaging traits that serve no useful purpose are rapidly weeded out of a population by natural selection. Mis-matched wings can spell doom, because animals with compromised flying ability are less likely to successfully feed themselves, find mates, and avoid predators.
When approaching females to mate, male Erebomyia were observed settling a few millimeters away and frantically fanning their wings. It could be that "the males are attempting to communicate," with buzzing sounds undetectable to the human ear, said Runyon. Females might use the quality of those sounds to detect differences between a male's right and left wings.
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