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Blister Beetle Toxicity

Blister beetles are members of the insect family Meloidae. Blister beetles get their name because when disturbed, they secrete a defensive toxin called cantharidin from glands at their leg joints, which may cause blisters or even oozing lesions upon contact with skin. They are extremely toxic to horses when the insects are accidentally ingested.
 
Blister beetles can contaminate alfalfa hay and only 6 grams of blister beetle can be potentially fatal to a full-grown horse. This toxicity doesn’t decrease when the beetle dies and even pieces of the beetle are toxic.
 
Blister beetles are a concern to hay producers throughout Tennessee. There is no antidote. The only way to prevent this toxicity to ensure you use a reputable source of alfalfa or to eliminate alfalfa from the horse’s diet. Your veterinarian can provide guidance and advise you on the real and relative risks.