Autotomy
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Autotomy (from the Greek auto = "self-" and tomy = "severing") or self amputation is the act whereby an animal severs one of its own appendages, usually as a self-defense mechanism designed to elude a predator's grasp. Geckos, skinks and other lizards that are captured by the tail will shed part of the tail structure and thus be able to flee. The detached tail will continue to wriggle, creating a deceptive sense of continued struggle and attracting the predator's attention away from the fleeing prey animal. The animal can partially regenerate its tail over a period of weeks. The new section will contain cartilage rather than bone and the skin will have different colouration, typically darker and with little or no pattern.
Autotomy in lizards is enabled by special zones of weakness at regular intervals in the vertebrae below the vent. Essentially, the lizard contracts a muscle to fracture the vertebra itself rather than break the tail between two vertebrae. Sphincter muscles in the tail then contract around the caudal artery to minimize bleeding.
Other animals, such as crabs, brittle stars, lobsters and spiders, can also lose and regenerate appendages when necessary for survival. Autotomy occurs in some kinds of octopus for survival and for reproduction: the specialized reproductive arm (the hectocotylus) detaches from the male during mating and remains within the female's mantle cavity.
The ejection of the guts of sea cucumbers when stressed is also a form of autotomy, and they regenerate the organ(s) lost.
The sting of various honey bee species is a different case; the sting apparatus is modified in such a way that it tears cleanly away from from the bee's body, and has its own ganglion that keeps the musculature of the sting shafts moving (thus embedding the sting deeper) and the venom sac pumping for several minutes after it detaches. Unlike most cases of autotomy, the bee dies shortly afterwards (they do not grow a new sting apparatus). No other stinging insect has the sting apparatus modified this way, including yellowjacket wasps, which also have barbed stings, but workers of all species of true honey bees (genus Apis). The sting of a queen honey bee has no barbs, however, and does not autotomize. Further, the genitalia of male honey bees ("drones") also autotomize during copulation, and form a "mating plug" which must be removed by the genitalia of subsequent drones if they are also to mate with the same queen. The drones die in the process.
