Swift and methodical, dragonflies can track the position of a tasty fly and steer itself strategically towards it—swooping in and snatching a meal in half a second. Researchers studying this predator’s acrobatic fly-catching maneuvers have discovered that dragonflies make meticulous internal calculations about the movements of its prey and its own body. The findings, published in Nature this week, are the first to show that insects have the same type of complex control—prediction and reaction —used by humans to seize moving objects.
You might not be aware of it, but every time you reach out for your mug, a series of sophisticated information processing has to happen. “You have an internal model of how your arm works, how the joints are articulated, of the cup and its mass. If the cup is filled with coffee, you incorporate that,” Anthony Leonardo of the Howard Hughes Medical Institute explains. “Articulating a body and moving it through space is a very complicated problem.”
Researchers used to think that invertebrates hunt by only reacting to (and not predicting) prey position and movement. “The idea was the dragonfly roughly knows where the prey is relative to him, and he tries to hold this angle constant as he moves toward the interception point,” Leonardo says in a news release. “This is the way guided missiles work and how people catch footballs.” But he guessed there was more.
Inspired by motion capture technology used to translate actors’ movements into computer animation, Leonardo and colleagues made high-speed recordings of dragonflies (Plathemis lydia) carrying retroreflective markers. Each time the team flashed a light, the reflection from the markers were recorded. These were designed to measure the orientation of the head and body as dragonflies hunted down fruit flies and artificial prey made of beads.
Dragonflies, they found, weren’t simply responding to the movements of prey. Their hunting maneuvers were generated by predictions of prey movement, combined with visual reactions to unexpected movements. These allowed them to estimate prey position and determine the wing and head movements needed for interception.
The dragonfly approaches from below to avoid detection, then aligns its body to the direction of motion of the prey directly overheard. The head locks onto the target and rotates continuously to stabilize an image of the prey, while the body maneuvers to the best position for prey capture. Pictured here, the 3D flight trajectory of a hunting dragonfly, showing the in-flight orientation of the head and body moving independently.
“It gives the dragonfly a very elegant combination of predicted model-driven control and the original reactive control,” Leonardo says. “At the end of the chase, the [dragonfly] makes a basket out its legs and the prey drops into it.”
If they were hunting reactively only, each steering movement from the prey would be matched exactly by one from the dragonflies, New Scientist explains. Instead, when the prey changes direction, the dragonflies stay true to their original course 70 percent of the time—they had clearly already plotted the interception path.
Images: Igor Siwanowicz, Leonardo Lab, Janelia Research Campus, HHMI (top), Anthony Leonardo, Janelia Research Campus, HHMI (middle)