Yes, blister beetles can kill horses.
Cantharidin is the poisonous substance in blister beetles. Very small amounts of cantharidin can cause colic in horses. The substance is very stable and remains toxic in dead beetles. Horses may be poisoned by ingesting dead beetles in cured hay.
Cantharidin can cause severe skin inflammation and blisters. It is absorbed through the intestine and can cause symptoms such as inflammation, colic, straining, elevated temperature, depression, increased heart rate and respiration, dehydration, sweating, and diarrhea. There is frequent urination during the first 24 hours after ingestion, accompanied by inflammation of the urinary tract. This irritation may also result in secondary infection and bleeding. In addition, calcium levels in horses may be drastically lowered and heart muscle tissues destroyed. Since animals can die within 72 hours, it is imperative to contact a veterinarian as soon as blister beetle poisoning is suspected.
