PHOTOGRAPH BY RASSIM KHELIFA
PHOTOGRAPH BY RASSIM KHELIFA

Why this insect fakes death to avoid sex

Acting dead allows the moorland hawker dragonfly to reproduce with the mate she chooses.

This story appears in the June 2019 issue of National Geographic magazine.

The mating ritual of the moorland hawker dragonfly—common around the ponds and wetlands of Europe, Asia, and North America—begins with what biologist Rassim Khelifa calls “an acrobatic aerial copulation.” While in flight, the female Aeshna juncea contorts so that her genitals, which are near the end of her body, connect with the male’s genitals, which are near his thorax. Thus joined in a lopsided-heart shape, they land and complete the sex act, whereupon the female will head off to lay her eggs.

Before she can do that, other males may show up seeking sex. Evolution predisposes her to resist: She has limited eggs, her reproductive tract can be damaged by repeated copulations, she’s already been inseminated by the mate she chose, and the dragonfly penis is structured so that it removes any sperm present before making a new deposit. So to avoid further sex, she may fall down dead—or more precisely, she may fake death, dropping from the air and lying motionless in the ground cover.

Watch: THIS FEMALE DRAGONFLY FAKES HER OWN DEATH TO AVOID SEX

At the University of Zurich, Khelifa conducted a study of the females’ death feigning and found that usually “their strategy works.” Most males buzzed the crash site briefly, he says, then flew off to look for other conquests. Once the males left, the lifeless-looking females stirred and went on their way.

Acting dead can be animals’ advantage

Assuming a lifeless-looking, immobile state in an effort to discourage or ambush a predator is known as tonic immobility, death feigning, or thanatosis. It’s been seen in a wide variety of vertebrates and invertebrates.

Hognose snake: To make their fake death throes as convincing as possible, hognose snakes of the North American genus Heterodon have been known to secrete a foul-smelling fluid and even spew blood.

Virginia opossum: When threatened, an opossum will faint and look quite dead—from its prone posture to its drooling, tongue-lolling grimace—which led to the phrase “playing possum” to refer to feigning death.

Predatory cichlid: At least two species of this fish may lure prey by sinking to the bottom of a river or lake and lying still as a corpse. If small fish approach to scavenge, the cichlid lunges and makes a meal of them.