Blister beetles

Blister beetles are members of a family of plant-feeding insects (Meloidae) that contain cantharidin, a toxic defensive chemical that protects them from predators. Accidentally crushing a beetle against the skin can result in a painful blister, the source of the insect’s common name. Blister beetles have long (3/4 to 1-1/4 inch) narrow bodies, broad heads, and antennae that are about 1/3 the length of their entire bodies. The front wings are soft and flexible in contrast to the hard front wings of most beetles.

In sufficient quantity, the cantharidin in the bodies of living or dead blister beetles can be toxic, and in some cases lethal, to horses, sheep, and cattle. The lethal dose is estimated to be between 0.5 and 1.0 mg of cantharidin per kilogram (2.2 lbs) of body weight. Cantharidin is very stable and remains toxic in dead beetles for a long time.