Anderson and her colleagues went a step further and programmed the Smellicopter to hunt for odors just like an actual moth would. If you’re able to smell an odor, there’s a good chance that the source is upwind from you. The same goes for insects like moths, who do something called cross-wind casting, in which they lock on to a presumably upwind source and fly toward it, and then shift their bodies left or right as needed to stay targeted on the odor. Anderson’s team trained the Smellicopter to do the same thing. “If the wind shifts, or you fly a little bit off-course, then you’ll lose the odor,” says Anderson. “And so you cast cross-wind to try and pick back up that trail. And in that way, the Smellicopter gets closer and closer to the odor source.”
The researchers call this a “cast-and-surge” algorithm: The drone moves toward a scent—in the lab they used a mixture of flower compounds—and tacks left or right if it loses the odor, then surges forward once it locks on again. The drone is also equipped with laser sensors that allow it to detect and avoid obstacles while it’s sniffing around.
And, boy, does it work well: The researchers have found that the Smellicopter gets to the source of an odor 100 percent of the time. That’s due in large part to the extreme sensitivity of a moth’s antenna, which can detect minute odors not on the scale of parts per million, or billion, but trillion. A moth further increases its efficiency with physics: As it flaps its wings, it circulates air over its antennae, helping to sample more of an odor. Here, too, the researchers took inspiration from nature, using the quadrotor’s spinning blades to move more air over their borrowed antenna.
Sure, at the moment humanity may not have much use for a moth drone that sniffs out flowers, so the researchers are now exploring ways to use gene editing to create moths with antennae that sense odors like those associated with bombs. But could these Frankenmoths possibly be as sensitive to the scents of human-made materials as regular moths are to the pheromones of potential mates and the smell of flowers? That is, can the researchers retune a sense of smell that evolution has perfected for the moth over hundreds of millions of years of evolution?
“Theoretically, you could get more sensitivity,” says Anderson, “because the moth antenna can sense a variety of different chemicals, a lot like how we can smell a variety of different things.” Her lab’s idea would be to genetically engineer a moth antenna to be chock-full of the particular protein that’s involved with sensing a desired chemical. That would focus the antenna’s powers on one odor, not many.