Blister Beetles and Alfalfa: A Potentially Lethal Mix

Blister beetles belong to a family of plant-feeding insects (Meloidae) that produce cantharidin, a toxic defensive chemical. Contact with it in the blood of live or dead beetles causes blistering of the skin or mucous membranes of sensitive mammals, especially horses. Cantharidin is stable and remains toxic in dead beetles for a long time, so animals can be poisoned by eating crushed beetles in cured hay.

The severity of the reaction depends upon the amount of cantharidin ingested and the size and health of the animal. The lethal dose for livestock is estimated to be 0.45 to 1.0 mg of the chemical per kilogram of body weight.

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