Thanatosis

Thanatosis, from the Greek thanatos meaning death, is a defensive behavior in which an animal feigns death to avoid predation. An animal practicing thanatosis typically becomes motionless, may drop limp, close its eyes, and greatly reduce movement and respiration. In some cases there may be a minimal odor or a change in posture to enhance the illusion of being dead. The behavior can last from a few seconds to several minutes, depending on the species and the threat.

Occurrence and examples: Thanatosis has been documented in a variety of taxa, including many insects (such as some beetles and grasshoppers), as well as in certain reptiles, birds, and mammals. The most familiar example in popular culture is the opossum, which is said to “play dead” when threatened. In other species, freezing or feigning injury can similarly reduce predation pressure by exploiting a predator’s expectations or biases.

Mechanisms and variation: The trigger is typically the perception of a threat or an actual capture attempt. The response can be influenced by the predator’s identity, the prey’s state, and environmental conditions. In some contexts, thanatosis may be followed by a sudden escape once the predator releases or loses interest.

Adaptive value: The primary function is to reduce predation by making the prey appear unpalatable, injured, or non-responsive. By lowering detectability through immobility, the prey may avoid further attack and gain a chance to escape.

Relation to other concepts: Some authors distinguish thanatosis from tonic immobility, the latter being a brief, reflex-like immobility induced by stress or handling rather than a deliberate death-feigning display.