Since most toxic substances emit some kind of odor, the wasps can be tricked if they are presented with the odor while feeding on whatever a wasp likes to eat. The odor becomes identified with food, so even a bomb could smell like lunch to a trained wasp.
Rains and Lewis tested that with explosive chemicals buried in the soil. The wasps detected the odor of the chemicals and set off the alarm, thinking food was nearby.
Rains and Lewis found it took less than five minutes to train each wasp.
"We feed them for 10 seconds, then take them away for at least 30 seconds, and we do that just three times," Rains says.
The trained wasps spend 48 hours inside the Wasp Hound, and then they are set free to enjoy the rest of their lives, normally about two or three weeks.
And that, unfortunately, is a big problem, and the researchers are struggling to resolve it. With such a short life span, the Wasp Hound doesn't have much of a shelf life. A new cartridge, with newly trained wasps, has to be inserted often, and they can't be stockpiled because the wasps can only be tricked for a little while.
If they smell the odor that they've been conditioned to associate with food, and they don't get any chow, they lose interest in the process rather quickly, Rains says.
So the researchers think they may have to set up a system where they could supply users with wasps very quickly. And that could take a lot of wasps.
As it stands now, each wasp is trained separately, but Rains and Lewis are working on a system that would allow them to train around 50 at a time.
And since it's easy to get them to reproduce, there should be no shortage of wasps, they say.
But the concept seems a bit cumbersome, so the future of the bomb-sniffing canine is probably secure.
Most likely, the scientists believe, there will be some applications for which the wasps are ideally suited.
"There are a few things we've been looking at," Rains says, "including food safety and some medical applications."
Some forms of cancer and stomach ailments produce odors, and wasps may be just what the doctor ordered.
"Lots of things can be detected if you know what to look for in your breath," Rains says.
If they've got to smell our breath, maybe it's a good thing that these wasps can't sting.