Dragonflies are ancient and complex insects, known for their brilliant colors and acrobatic flight. Their lives revolve around the water where they breed, making them a common sight around ponds and streams. Female dragonflies employ an extraordinary tactic to manage unwanted attention from males: they appear to fall dead from the sky. This unusual phenomenon is a remarkable example of behavioral adaptation.
Confirmation of Death-Feigning Behavior
Scientific study confirms that females of certain species, such as the moorland hawker dragonfly (Aeshna juncea), engage in a behavior often described as feigning death. This act, known scientifically as thanatosis, is an established anti-predator defense found across the animal kingdom. The first formal documentation of this behavior as a response to sexual harassment occurred in 2015 in the Swiss Alps. The behavior is triggered almost exclusively when a non-receptive female is pursued by a male attempting to force a mating. Females who continued flying were almost always intercepted and mated with, highlighting the effectiveness of the extreme tactic.
This response is a deliberate strategy of last resort. In one study, females feigned death in over 75 percent of observed male pursuit instances, demonstrating it is a common tactic for evading coercion. Avoiding mating rather than a predator makes this a rare example of “sexual death feigning” among animals.
The Mechanics of Playing Dead
The physical performance of feigning death is sudden and dramatic, beginning while the female is still airborne. When a persistent male begins a chase, the female halts her flight and plummets to the ground in a sudden dive. She often falls into dense vegetation or onto the ground, where she remains completely motionless.
Upon landing, the female frequently adopts an unusual and unnatural posture, sometimes lying upside down or with her body curled. The male, relying on movement and color to track his target, typically hovers briefly over the motionless insect before flying away, convinced the female is no longer viable. Once the male suitor has departed, the female quickly takes flight. The ruse is successful in a majority of cases, with one study noting a success rate around 77 percent.
The Underlying Evolutionary Motivation
The motivation behind this risky behavior centers on the concept of sexual conflict, which arises when the reproductive interests of males and females diverge. For a female dragonfly, mating once is usually sufficient to fertilize all her eggs, but males benefit from mating as often as possible to maximize their paternity. Unwanted, subsequent mating attempts are costly for the female, who is often intercepted while searching for an appropriate site to lay eggs.
Costs of Unwanted Mating
Further matings can be physically damaging, as the male often removes the sperm of previous mates, which can injure the female’s reproductive tract. Additionally, the struggle and copulation process consume valuable energy and time that the female needs for oviposition (egg-laying). By feigning death, the female effectively removes herself as a responsive stimulus, deterring the male and allowing her to conserve energy and avoid physical harm. This extreme form of resistance enhances the female’s overall reproductive fitness by ensuring she survives to successfully lay the eggs fertilized by her chosen mate.