Moth navigation probed to improve micro-drone flight

It turns out moths are far better at video games than we might have thought. When navigating through a virtual forest, hawkmoths determine their route ahead of time depending on how much of the forest they can see. Mimicking their strategy might help us improve the flying ability of the micro-drones now being built.

Moths certainly see the world differently from humans as they zip along at 25 wingbeats per second. To figure out how they use landmarks to aid their navigation, Yonatan Munk of the University of Washington in Seattle created a virtual forest containing various amounts of "fog" that obscured the virtual trees. He then tied a hawkmoth (Manduca sexta) to an input device in front of the screen. This device detected when the moth was turning and caused the visualisation to respond accordingly.

"I'm essentially giving the moth a joystick," Munk said at the Society for Integrative and Comparative Biology meeting in San Francisco, where he presented the research last week.

The simple animation (see video) tricked the moth into navigating through the trees it saw. Similar techniques have been used to fool fruit flies, mice and fish. When the insect thought it was about to crash into a tree, it would often flail its legs as though trying to land or slow down.

Munk and his colleagues set up three virtual environmental scenarios to see whether moths always navigate through trees in the same way. Surprisingly, they found that the moths changed their strategy depending on visibility conditions.

If virtual "fog" rendered visibility so poor that the moth had just quarter of a second to respond to approaching obstacles, it would fly in wide circles until it found a tree, which it then used as a reference point.

Next, the researchers lifted the virtual fog slightly, giving the moth about 2 seconds to respond to obstacles. Now, if trees loomed to the left or right, the moths veered sharply towards them.

Information filter

Finally, with no fog at all, the moth could see trees even a virtual kilometre away. Now there was no longer a correlation between the moth's left and right turns and the total number of trees visible to its left or right, says Munk. However, there was a correlation between its turns and the number and position of nearby trees – in other words, moths ignored visible distant trees when navigating in very clear conditions.

It's interesting that the moths appear to plan their strategy ahead of time depending on how much of their environment they can see, says Mark Willis of Case Western University in Cleveland, Ohio. "We're used to thinking of insects as little stimulus-response machines."

By controlling what an insect encounters in a virtual reality world, researchers can tease apart how the creatures integrate different sensory inputs while navigating, says Willis. This information is important if we are to design effective flight navigation algorithms for micro-drones similar in size to the moths. "We're starting to understand what's going on in those beady little bug brains," Willis says.

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