Autotomy or self amputation is the behaviour whereby an animal sheds or discards one or more of its own appendages, usually as a self-defense mechanism to elude a predator’s grasp or to distract the predator and thereby allow escape. The lost body part may be regenerated later.
Some geckos, skinks, lizards, salamanders and tuatara 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 distracting the predator’s attention from the fleeing prey animal. The animal can partially regenerate its tail, typically over a period of weeks. The new section will contain cartilage rather than regenerating vertebrae of bone, and the skin of the regenerated organ generally differs distinctly in colour and texture from its original appearance. The technical term for this ability to drop the tail is caudal autotomy. In most lizards that sacrifice the tail in this manner, breakage occurs only when the tail is grasped with sufficient force, but some animals, such as some species of geckos, can perform true autotomy, throwing off the tail when sufficiently stressed, such as when attacked by ants.
At least two species of African spiny mice, Acomys kempi and Acomys percivali, are capable of autotomic release of skin, e.g. upon being captured by a predator. They are the first mammals known to do so. They can completely regenerate the autotomically released or otherwise damaged skin tissue — regrowing hair follicles, skin, sweat glands, fur and cartilage with little or no scarring. It is believed that the corresponding regeneration genes could also function in humans.
Autotomy occurs in some species 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.
Species of (land) slugs in the genus Prophysaon can self-amputate a portion of their tail. There is known autotomy of the tail of sea snail Oxynoe panamensis under persistent mechanical irritation.
Evisceration, the ejection of the internal organs of sea cucumbers when stressed, is also a form of autotomy, and they regenerate the organ(s) lost.
Autotomic stone crabs are used as a self-replenishing source of food by humans, particularly in Florida. Harvesting is accomplished by removing one or both claws from the live animal and returning it to the ocean where it can regrow the lost limb(s). However, under experimental conditions, but using commercially accepted techniques, 47% of stone crabs that had both claws removed died after declawing, and 28% of single claw amputees died; 76% of the casualties died within 24 hours of declawing. The occurrence of regenerated claws in the fishery harvest is low; one study indicates less than 10%, and a more recent study indicates only 13% have regenerated claws.
Under natural conditions, orb-weaving spiders (Argiope spp.) undergo autotomy if they are stung in a leg by wasps or bees. Under experimental conditions, when spiders are injected in the leg with bee or wasp venom, they shed this appendage. But, if they are injected with only saline, they rarely autotomize the leg, indicating it is not the physical injection or the ingress of fluid per se that causes autotomy. In addition, spiders injected with venom components which cause injected humans to report pain (serotonin, histamine, phospholipase A2 and melittin) autotomize the leg, but if the injections contain venom components which do not cause pain to humans, autotomy does not occur.