According to a brief story in Science (November 25), entomologist W. Joe Lewis of the U. S. Department of Agriculture found that he could train wasps to detect and react to scents associated with explosives. And he could do it in five minutes by associating the scents with a sugar-water reward.
Of course, you can't put a wasp on a leash like an explosive-sniffing dog. So Lewis designed a portable "Wasp Hound," a device with a fan that pulls air into a chamber with trained wasps. When the target scent appears, the wasps crowd around the intake looking for a reward. According to Lewis, they do the job as good as a trained hound, far more cheaply.
OK, what next? I suppose wasps are too small to carry transmitters so that their free-wing searches for suspect molecules can be tracked. On the other hand, yelps of pain from explosive-handling terrorists might do the job better than radio.
But then innocents might get stung too. So here's my idea: Train butterflies. Flocks of explosive-sniffing butterflies would add a lovely note to otherwise drab airport terminals and public buildings. Security personnel would keep an eye out for persons in a cloud of fluttering wings.