‘We have a way of steering a fly like you would a car’

Fruit flies, one of the most studied organisms in science, are efficient little creatures, able to navigate their environment with agility. They were also one of the first animals to be manipulated by geneticists.

A new study, published last month by PNAS, exploited these qualities by turning fruit flies into what the co-authors call “living micro-robots,” whose movements can be controlled by sensory clues. The paper was completed at Harvard’s Rowland Institute, dedicated to experimental research across engineering and science disciplines.

“Typically, people think about robots as devices that you build with plastic and metal and the wires and software,” said co-author Aleksandr “Sasha” Rayshubskiy, a fellow at the Rowland Institute. But because fruit flies — aka Drosophilae melanogaster — are so well understood, they can be treated as living robots.

“You can get them to do things that you want them to do,” Rayshubskiy said.

The research team used two methods to manipulate the flies’ movements, the first involving light and a wheel. “We can rotate the light and wheel either clockwise or counterclockwise, and that makes the flies turn,” explained Charles Neuhauser, a postbaccalaureate fellow on the study.

The second method involved scent, again used to get the flies to one side. “We get them to think that they are smelling something either to the left of their body or to the right of their body,” Neuhauser said.

The paper describes how these controls were used to lead flies through a maze and block out phrases like “Hello, world,” a familiar greeting to computer programmers. “We can hack their genes to turn on actions,” said co-author Kenichi Iwasaki, a research associate at the Rowland Institute. “We can hack them the same way that you would hack a conventional robotic system. We have a way of steering a fly like you would a car.”

But do these flies really constitute robots? “Our work pushes that conceptual boundary,” Rayshubskiy said. “I think a robot is a machine that you can get to do useful work for you.”

The project is the result of “two fields that normally don’t interact,” he added. “You have the field of engineering where people build robots. They don’t really see the fly as a player yet in that world. And then you have a field of people who care deeply, very deeply about fruit flies, but they don’t really venture into the robotic field.

“I’ve engineered myself into this bridge between these two fields,” Rayshubskiy said.

Although the fruit fly’s 1 mg, 2.5 mm body is tiny, Rayshubskiy sees multiple possibilities for future applications. “They can carry about their own weight,” he pointed out. “We could not only guide them places, but we can also activate behaviors inside of them where they could do something else.”

He gave a practical example. “It’s actually really hard to clean buildings,” Rayshubskiy said. “They’re covered in junk constantly and it builds up over time. Imagine having a swarm of fruit flies, thousands and thousands of flies, that you could direct onto the face of a building, and they would clean all the dirt that builds up. You could use swarms of flies as cleaning devices.”

A second paper, currently being finalized by the same set of researchers, addresses how fruit flies can be made to interact with foreign objects, essentially exploring their potential as tiny beasts of burden.

“Our work provides a foundation for deploying swarms of natural ‘robots’ that, with further innovations, could transform applications like environmental monitoring and disaster response,” said Rosy Hosking, director of research affairs at the Rowland Institute.

The forthcoming research also gives insight into the workings of the fruit fly brain. “There’s tension between our guidance, which doesn’t know or care about how the fruit fly feels, and the fly’s own feelings about what feels safe to do,” Rayshubskiy said. By studying that tension, and the fruit fly’s responses, he said, “We could tease out the hidden variables about what the fly cares about by forcing it to do certain things.”