People living in coastal areas sometimes feel that they are little more than meals for a blood-sucking pest: the sand fly. Now, University of Florida entomologist Jonathan Day has come up with a way to reduce sand fly populations by taking advantage of the very mechanism that enables these pests to find their prey. Sand flies are attracted to the CO2 exhaled by living organisms. Day built a fence that attracts the flies by emitting a carbon dioxide mixture through PVC pipes, then traps them in fabric panels covered with mineral oil. The fence could be used in sporting complexes, playgrounds or backyards. Over a three-year period, about 180 meters of fencing along a mangrove-lined canal in Vero Beach, Fla., cut the sand fly count by a factor of three, says Day. Air Liquide, a gas supplier whose U.S. R&D operations are in Chicago, has patented the trap.