Some lizards exhibit a fascinating survival tactic known as playing dead. This natural defense mechanism helps them protect themselves when confronted by a threat, increasing their chances of survival.
The Phenomenon of Playing Dead
This behavior is scientifically referred to as thanatosis or tonic immobility. It involves the lizard entering a state of apparent death, becoming completely motionless and unresponsive to external stimuli. This involuntary reaction is triggered by extreme stress or a direct threat. The lizard’s brain initiates a state of temporary paralysis, often when escape is no longer possible.
The duration of this immobility varies, ranging from a few seconds to several minutes, depending on the species and perceived danger. The lizard maintains this state until the threat passes, then abruptly revives and attempts to escape. This defense mechanism is a last resort, occurring after physical contact with a predator.
Why Lizards Play Dead
The primary purpose of thanatosis in lizards is to avoid predation. Predators prefer live prey and are deterred by an animal that appears dead. Mimicking a deceased animal convinces a predator the lizard is not a viable meal, as some predators are wary of consuming diseased or decaying animals. This behavior makes a motionless lizard less noticeable to predators that rely on movement to detect their prey.
Playing dead also creates an opportunity for the lizard to escape. If a predator’s attention is diverted or it momentarily relaxes its grip due to the lizard’s apparent lifelessness, the lizard can quickly flee. The sudden “revival” of a lizard playing dead startles a predator, providing an additional chance to get away. This strategy is useful when other defense mechanisms, such as camouflage or rapid escape, have failed.
How Lizards Play Dead
When exhibiting thanatosis, lizards adopt specific physical postures to create the illusion of death. They typically become completely still, sometimes rigid or entirely limp, mimicking a deceased animal. Many lizards will flip onto their backs, exposing their underside, which can reinforce the appearance of carrion to a predator. Their breathing may become shallow and irregular, further contributing to the imitation of a lifeless state.
Some species may also close or half-close their eyes. To make the deception more convincing, certain lizards might exhibit open-mouthed gaping, displaying their tongue, or even release foul-smelling secretions from their cloaca. These sensory cues, particularly the unpleasant odor, can further deter predators that rely on scent. Physiological changes, such as a reduced heart rate, also contribute to the impression of being lifeless.
Lizards Known for This Behavior
While not all lizard species exhibit thanatosis, it is a documented strategy in several groups. Anoles (Anolis spp.) freeze in place or flip onto their backs when threatened. Skink species also employ this defensive strategy, including the spotted forest skink (Sphenomorphus maculatus) and Leposoma scincoides, which turn onto their backs with eyes closed upon handling.
Fence lizards, such as the Eastern Fence Lizard (Sceloporus undulatus), can become stiff and still, resembling a dead twig or leaf. The Texas Horned Lizard (Phrynosoma cornutum) is another example, known for its ability to remain motionless for an extended duration. The Italian Wall Lizard (Podarcis siculus) has also been observed displaying tonic immobility, even without direct physical handling, indicating it can be a response to the mere presence of a threat.