Many insects voluntarily discharge blood in response to a threat. This behavior, autohemorrhaging, may serve as a physical deterrent (e.g., by enveloping a potential predator or by exposing the predator to noxious substances). Many beetles in the Chrysomelidae, Meloidae, and Lampyridae are well known for this behavior, which is also called reflex bleeding. For example, the blood of blister (meloid) beetles exposes potential predators to the noxious substance cantharidin. Species apparently release blood through an increase in hydrostatic pressure. When the hydrostatic pressure returns to normal levels, much of this blood is withdrawn into the insect's hemocoel, and so little is actually lost from the insect.

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