A new way to stick it to flies. (Physics).

Walk on carpet and you may build up enough static electricity to generate a little shock. Researchers are now capitalizing on the phenomenon to trap insects.

The bizarre strategy is to let the critters charge up as they walk, then use this electricity to attract oppositely polarized poisonous particles--like a magnet gathering iron filings.

Static builds when one material transfers electrons to another by repeated contact. Insects accumulate static charges as they fly or walk. One ecological benefit of this is that pollen grains stick to the insects, which then carry them to flowers. Until now, however, no one has actually measured the amount of charge involved.

Now scientists have done so. Their tack was to allow flies to accumulate charge as they wandered over different materials. The researchers measured the distance walked and the number of footsteps taken and then put the insects into thimble-size metal pails to measure the charge transferred.

In the February Journal of Electrostatics, the researchers report that this charge is proportional to the number of footsteps taken by the fly and not to distance walked. They also report that polyvinyl chloride was the most effective tested material at generating a charge.

The amount of electricity involved in each case was tiny, but it may be enough for developing a new type of trap, says coauthor Chris W. Jackson of the University of Southampton in England.

Jackson's team is developing traps that use pheromones to draw insects across surfaces that are dusted with insect-killing fungal spores. The surface charges up the fly, and the spores stick to the hapless victim. A faster-acting, but less environmentally friendly trap could be created using pesticide particles instead of fungal spores, says Jackson.

"It's certainly a novel approach," says Jerome A. Hogsette, a fly-control specialist at the U.S. Department of Agriculture in Gainesville, Fla. "We rarely look to physics" for insect control, he adds. --J.P.