A new study uses a robotic flower to suggest that the night vision of the hawkmoth is linked to the swaying of flowers in the breeze. (Sponberg Lab, Georgia Tech)

It turns out that one moth's night vision may be perfectly dialed in to its primary source of food. In a study published Thursday in Science, researchers report evidence that the hawkmoth (Manduca sexta) has used the movement of the flowers it eats as a guide for how to change its eyesight at night.

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Scientists already knew that moths -- and in particular the hawkmoth -- have a really intricate way of seeing in the dark. They're able to hover perfectly in extremely low light, an impressive feat of both vision and motor control. They do this by adjusting their compound eyes the way an aperture adjusts on a camera, opening up to allow more light in. But some hypothesized that they also used another camera-like trick: They slow their brains down to allow more time to process the light they do take in.


Manduca sexta has large compound eyes, the better to see you in the dark with. (Armin Hinterwirth)

But how to prove that moths had mastered long exposure photography? Lead study author Simon Sponberg and his colleagues realized that such a brain mechanism would leave behavioral traces that they could catch on camera.

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"Using this temporal strategy is sort of like changing the shutter speed on a camera to increase exposure," Sponberg told The Post. "And if you do that with a series of frames, each gets brighter, but also blurrier. It gets harder to see fast things."

If moths slowed down their brains to let in more light, Sponberg figured, difficulty following fast objects would be the consequence. So he and his team built robotic flowers that they could have "sway" at specific speeds. Sure enough, the moths lost their ability to track flowers in the dark and hover in front of them as they swayed if the swaying got too fast.

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"We saw that in low light, there was a very abrupt cut off at a flower moving faster than two times a second," Sponberg said. "And we wondered what was so special about that speed."


A hawkmoth clings to a robotic flower used to study the insect's ability to track the moving flower under low light conditions. The research shows that the creatures can slow their brains to improve vision under low light conditions while continuing to perform demanding tasks. (Rob Felt, Georgia Tech)

That speed was indeed quite special: When Sponberg's team tested the five flowers that provide most of a hawkmoth's sustenance, they realized that the moths had modulated their night vision to track those specific plants in the dark. In those plants, 94 percent of the movement researchers recorded was below that cut off.

"The take home is that moths probably do slow their brains down in order to be more sensitive to low light, but only just to the point where it would actually hurt their ability to do what they need to do," he said.

Now the team will go looking for the actual mechanism in hawkmoth brains. But they're also going to look for similar adaptations in other creatures.

"It would make sense for other moths, that fly at other light levels and go after other flowers, to be tuned in to other speeds," he said.

But Sponberg has no particular fondness for moths. To him, the findings speak more broadly to the fascinating intricacies of the brain -- even a tiny one.

"Even the small brains of insects are capable of a huge variety of behaviors," he said.

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