To many horse owners, purchasing hay has become science: Select the type of hay, grab a handful for the smell test, examine it for dust and mold and then feed it to the hungry horse awaiting for you at home. Many hay producers will be, or have already been harvesting hay and have started selling their product to horse owner consumers. But as hay purchasers we must be aware of a tiny, toxic and potentially fatal tagalong in some perfectly healthy-looking alfalfa hay bales – the blister beetle.
Blister beetles are from the Meloidae family so called for their defensive secretion of a blistering agent, cantharidin and come in many sizes, shapes and colours. There are about 7,500 known species worldwide. Cantharidin is a poisonous chemical that causes blistering of the skin and is highly toxic to horses. A few beetles consumed in a single feeding of alfalfa can be lethal.
Blister beetles tend to swarm to feed on alfalfa flowers and simply touching a blister beetle, either dead or alive, is enough to cause inflammation and blistering of a horse’s skin within hours of contact.
If a horse ingests even a few beetles, the insects’ cantharidin can cause ulceration and inflammation of the mouth, stomach and intestines. Clinical signs including decreased appetite, frequent drinking and urination, colic, and depression can be apparent with hours. In the worst case scenario, ingesting these beetles can cause endotoxemia, shock and death within hours of ingestion.
If you suspect your horse has ingested blister beetles, immediately call your vet and most likely you will need to transport your horse to the nearest equine hospital for treatment. There is no specific antidote for blister beetle poisoning. Treatment is solely aimed at reducing absorption of the toxin by administering activated charcoal and mineral oil, intravenous fluids, gastrointestinal protectants and broad spectrum antibiotics.
So, before feeding your horse that bale of alfalfa hay, examine it carefully for the presence of blister beetles.