Avoiding death by feigning death.

Thanatosis is a common phenomenon in which prey appear to feign death when attacked by predators. It was once widely believed that thanatosis exploited predators' tendencies to avoid dead prey. However, this hypothesis has never been tested, and its feasibility has been questioned to the point that it has been largely abandoned [1,2]. Here, I show that naive birds quickly learned that dead Indian stick insects Carausius morosus were unpalatable, and subsequently rejected live insects that displayed thanatosis, but not those that failed to show thanatosis. Thanatosis had no effect on the behavior of birds that had never experienced dead insects, or those that had experienced dead insects whose resemblance to thanatosic insects had been destroyed. Therefore, thanatosis clearly caused predators to avoid prey that they mistakenly perceived to be dead.