Fighter pilots training for stealth combat missions ought to have a lot of respect for dragonflies. These airborne predators employ an optical illusion to stalk other flies who invade their territory. They project themselves as a stationary object while speedily dive-bombing their victims, new research suggests. These findings, which appear in the 5 June issue of Nature, illustrate for the first time how dragonflies use complex camouflaging techniques during aerial combat.
Dragonflies have inhabited Earth for more than 300 million years, making them ancient even by insect standards. Territorial disputes are common among these crafty critters, which chase intruders at high speeds for long distances and often slam into them in midair. The stakes are high, as the contests determine which males get the first-rate females and supreme egg-laying sites.
Akiko Mizutani, a biologist at the Centre for Visual Sciences at the Australian National University in Canberra, filmed dragonflies zipping around a large pond. She used a pair of cameras, which allowed her to determine the flies' position in three dimensions. Mizutani and her colleagues then reconstructed the insects' flight patterns on a computer. They observed that the dragonfly that's on the offensive maneuvers so that it always appears on the same region of its rival's retina. To the opponent, this means the aggressor will appear motionless even when it is actually coming closer. Exactly how the flying predator calculates the necessary movements and regulates its flight so precisely, slipping sideways and changing course in milliseconds, remains a mystery.
"Nature has probably selected for good aerial combat,” says Javaan Chahl, an engineer and biologist at the Defence Science and Technology Organisation in Edinborough, South Australia, and a co-author on the paper. Out of 14 combat episodes, six exhibited what the team calls “motion camouflage.” The researchers are now developing algorithms to more precisely map out how the dragonfly pulls off its clandestine maneuvers.
“Just as an observation, this is an intriguing result," says Sarita Thakoor, a physicist at the Jet Propulsion Laboratory in Pasadena, California, who works on robotic flight systems based on ideas gleaned from insects such as dragonflies and bees. “I can recognize that the defense world would probably be interested,” she adds.