Male dragonflies are known to engage in mid-air “dogfights” to defend their breeding territory, using different maneuvers than those they employ when hunting prey. A new paper published in the Journal of the Royal Society Interface concluded that relatively simple rules drive that behavior, namely that male dragonflies are trying to maintain a tactical position. This mirrors the tactics of human fighter pilots. The research could lead to the development of smarter drones capable of navigating with simple, vision-based guidance rather than complex computation.

Classic pursuits involving prey or mating rituals are asymmetric: there is a chaser and an evader, with each role requiring different maneuvers. In the case of male-on-male interactions, however, it is more of a mutual pursuit, per the authors, who thought that studying flight trajectories of insects or raptors could yield useful insights into the guidance laws that underlie the behavior. They chose the Trithemis Aurora species of dragonfly for study because the males are “fiercely territorial,” and there are usually multiple males around a given pond, intent on defending their chosen perches. The dragonflies are also crimson-colored, making them easier to track.

Much of the prior research on dragonfly interactions relied on visual observations or single-camera recordings. For this study, the authors set up a portable stereovideographic rig with two shutter-synchronized cameras to record dragonfly interactions in both color and monochrome, and then reconstructed 102 paired male-on-male flight trajectories to capture the 3D kinematics. They also reconstructed nine trajectories for dragonflies intercepting prey for comparative purposes. This enabled the authors to develop a model for the rules governing the flight behavior.

Chasing the tail

The resulting analysis confirmed marked differences in flight behavior when dragonflies were hunting prey versus defending their territory from other male dragonflies via “dogfight” displays. When hunting, the dragonflies approached their prey from below, so prey was often viewed silhouetted against the sky. Dogfighting males showed more highly convoluted trajectories and were more likely to be viewed against a background of foliage or the ground.