Autotomy is a defensive response to attack involving the amputation or active breaking of a body part along a breakage plane and usually involves loss of a leg. Many invertebrates (e.g., crayfish, daddy-long-legs), including insects such as crickets, grasshoppers, and walkingsticks, and many vertebrates (e.g., salamanders) exhibit this ability. For example, walk-ingsticks (Phasmida) have weakened areas at the trochanter that break under stress, such as when an appendage is grasped by a predator. If the insect is not an adult, regeneration occurs at the next molt. The amputated leg of the walkingstick twitches after being detached, which may divert the predator's atten tion away from the attacked insect. A grasshopper, when held by a hind leg, can voluntarily discard that limb by intense muscular contraction and rupture it at the trochanter—femur junction; autotomy can also be induced by mechanical pressure or electrical shock. The individual may benefit from the loss of limb by surviving the potential predator but loss of balance, reduced ability to forage for food, and reduced ability to escape from the next predator result as well.

Sting autotomy, the self-amputation of the stinger and its glands, occurs in many social Hymenoptera as part of colony defense, especially against vertebrates, and may occur because of the size and shape of the sting barbs. Chemical cues released by the detached venom apparatus may enable other attacking individuals to orient themselves to the predator.

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