Clues to night flight wind-drift correction.

Clues to night flight wind-drift correction

Radar operators, as well as entomologists, marvel at the ability of some insect swarms not only to maintain a constant compass orientation -- even when flying at extremely high altitudes on moonless nights -- but also to correct for displacement by crosswind drift. Unable to know that the "parcel" of air they are flying through is itself on the move, how do these insects keep their flight paths on target, relative to the ground? Scientists are more than simply curious about this; they note that an understanding of the migratory abilities of insects such as locusts and some moths might help them forecast insect movements and design novel pest controls.

"It has already been established that low-flying insects use visual cues to steer in a wind," says Chris M. Addison, of the Imperial College at Silwood Park, Berkshire, England. Additionally, "Theoretical work suggests that moths may be able to detect ground features at starlight illumination." But empirical evidence of this is lacking, he says, and some scientists doubt that visual cues can be of much help to high-flying moths and other insects that manage to stay on track at night while crusiing at altitudes of hundreds of meters.

To find out what an insect can and cannot do under such conditions, Addison hs designed a "flight simulator" for bugs with the Right Stuff. A live insect is glued to a horizontal needle that is attached to a sensitive torque meter. While the bug is suspended over a screen in a darkened room, moving images are projected from below at varying directions and lightings. The torque meter measures the insect's attempts to make in-flight compensatory turns in response to the imagery; the data are digitized and stored in a computer for analysis.

Addison hs no answers yet, but a previous experiment using a specially designed wind tunnel suggested that visual cues are not the key to wind-drift correction. Insteead, he says, insects may detect occasional, small-scale air movements within a larger air mass, providing clues about the larger mass's speed and direction.