Watch Out, Stephen Curry, Moths Have Hand-Eye Coordination, too

This moth has the longest proboscis of any insect. (Photo ©Minet et al. 2021)

You’ve heard the story about how Darwin was once examining an orchid from Madagascar with the nectar pooled at the bottom of a spur that was more than a foot long. “Good heavens,” he wrote to a friend, “what insect can suck it!” Given the way flowers and their pollinators co-evolve and sometimes become obligate partners, entirely dependent on each other, Darwin (and Alfred Russel Wallace, too!) predicted there must be a moth with a proboscis at least equally long to feed on that nectar. In fact, the predicted hawkmoth (Xanthopan praedicta) turned up in Madagascar 40 years later, with a proboscis up to 15 inches long. 

As you might imagine, a proboscis that long, or really any length, is too awkward to carry around fully extended, especially when you fly the way a hawkmoth flies. Instead, the hawkmoth rolls it up neatly for flight and, upon arriving at a flower, stops on a dime, hovers expertly, and unrolls it again. As the flower nods in the breeze, the hovering moth probes with surgical precision deep within. Shades of Stephen Curry dropping three-pointers.

The question a new study investigates is whether the moth uses the equivalent of hand-eye coordination to find its way with such accuracy to the flower’s nectar. That kind of control is mostly found in bigger, more complex animals, mainly mammals and birds. There’s a reason for that: Sören Kannegieser and his co-authors describe that kind of coordination as “an intricate neural control task, including visually identifying the target’s position in 3D space, passing the representation to the motor system, and enacting control commands to the respective appendages.” The human brain, which contains about 86 billion neurons, is up to intricate tasks requiring hand-eye coordination. But there are only about a million neurons in a hawkmoth’s brain.

So the researchers devised various ways to study how the hawkmoth does it, by carefully distinguishing active movements of the proboscis from passive ones caused by how the rest of the moth’s body is moving. It would be difficult to do that by setting up high speed cameras and other equipment in the rapidly changing conditions among the flowers in a real garden. (OMG, rain!) So they painted flower patterns on a vertical surface in the laboratory. Does this remind you of the faux cave entrance painted on a cliff face in the “Wile E. Coyote & Roadrunner” cartoons? The hawkmoths were, in fact, deceived by the faux flowers. But unlike Wile E. Coyote, they did not smash face-first into the surface. Instead, they used their proboscis for the sort of delicate probing they specialize in, and the muscles in the proboscis controlled this movement independently of the movement of the rest of the moth’s body. 

Then the researchers wanted to know if the moths were using vision to aim these probing movements. So they blocked the moths’ vision, in one eye or the other, as they approached the target. A variety of other manipulations allowed the researchers to conclude that the moths use “flight control for coarse visual targeting, but rely on visual proboscis guidance to fine-tune their probing position.” That is, they possess the insect equivalent of hand-eye coordination.

The authors of the new study think this could make the hawkmoth “a model for the analysis of neural control strategies underlying eye–appendage coordination.” Meantime, it’s just one more good reason to admire hawkmoths (at least when you do not happen to be hating them).