To find out how dragonflies prepare for their prey’s movements during a hunt, researchers built a fruit fly Colosseum, complete with fake scenery and high-speed cameras — and then hooked up the dragonflies with smaller versions of the reflectors used in Hollywood’s motion-capture studios.
The result? The scientists found that the dragonflies tracked the movements of fruit flies (and artificial flies) with sophisticated head and body movements, and then adjusted their route to intercept them. In this week’s issue of the journal Nature, the research team says such computational models for tracking targets have not been previously described in insects, but are similar to the neural processes seen in vertebrate animals — like humans, for example.
Sensorimotor control in vertebrates rely on internal models. When extending an arm to reach for a certain object, the brain uses predictive models of both limb dynamics and target properties.
Whether invertebrates use such models remains unclear. Here we examine to what extent prey interception by dragonflies (Plathemis lydia), a behavior parallel to targeted reaching, requires internal models.
“This highlights the role that internal models play in letting these creatures construct such a complex behavior,” senior author Anthony Leonardo, a researcher at the Howard Hughes Medical Institute’s Janelia Research Campus, said in a news release. Leonardo and his colleagues went to great lengths to build a customized fly-killing arena because dragonflies typically refuse to chase prey in controlled, indoor settings.
For each test, dragonflies took off to pursue prey from a launch pad that was surrounded by artificial scenery to mimic the animal’s natural habitat. Analysis of the flight paths and head movements captured on camera enabled Leonardo’s team to work out whether the insects were hunting reactively or predictively.
By simultaneously tracking the position and orientation of a dragonfly’s head and body during flight, we provide evidence that interception steering is driven by forward and inverse models of dragonfly body dynamics and by models of prey motion.
Predictive rotations of the dragonfly’s head continuously track the prey’s angular position. The head–body angles established by prey tracking appear to guide systematic rotations of the dragonfly’s body to align it with the prey’s flight path.
Model-driven control thus underlies the bulk of interception steering movements, while vision is used for reactions to unexpected prey actions. These findings illuminate the computational sophistication with which insects construct behavior.