A. The insects you see swarming around a streetlamp on a hot summer night aren't so much attracted to the light as disoriented by it, says UW-Madison entomologist Phil Pellitteri.

One common explanation for why this happens pertains to moths and other insects that orient to the moon. Flying at a steady 15-degree angle to the moon's distant glow allows moths to travel a straight course for long distances, Pellitteri says.

But when they try to fly at a constant angle to something close by, such as a porch light, the strategy sends them looping in circles -- essentially trapping them.

This theory doesn't explain, however, why light also captures creatures such as beetles and mosquitoes that don't navigate by the moon. What likely happens in their case is that bright light at night simply blinds them, much like it does people.

"A lot of insects are quite light-sensitive because they're night-flying to begin with," says Pellitteri. "And then when they (encounter) a tremendous light source, they just get confused. They can't see where they are." As a result, they end up fluttering randomly around the light, rather than flying away.

What's bad for insects is good for entomologists, though, because light is a handy collection tool.

"Typically you use a white sheet, so you have a larger area, and a light source that is heavy on the UV side," says Pellitteri. "Then you get all kinds of neat critters."

-- Produced in cooperation with University Communications

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