horses beware

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Margined blister beetle, Epicauta pestifera

Cantharidin. Can-thar-i-din. 

It's a poisonous chemical, a bitter crystalline compound that causes blistering of the skin and is often used medially to remove warts. Should you need to mix up a batch of the blistering agent in your basement, it's C10H12O4 or ten parts carbon, twelve parts hydrogen and four parts oxygen, hold the mayo. 

Naturally occurring, cantharidin is a toxic oily liquid secreted by blister beetles when they are threatened, picked up or forced to watch a movie like any of the Smokey and the Bandit offerings. Sally, what were you thinking?

There are approximately 7,500 known species worldwide, so there's a lot of blistering going on out there. The one I encountered and photographed was ash gray, but other species are brightly colored, announcing their toxicity to would-be predators.

The blister beetle genus Epicauta—and the one I found with Rikki Hall and a group from Ijams is perhaps Epicauta pestifera, the margined blister beetle—is generally found in farm fields. Their larvae feed on the eggs of grasshoppers, which I would imagine are enormously hard to find but I'm not a blister beetle larva. I have trouble finding my keys every morning.

As adults, blister beetles are highly toxic to horses. A few consumed in a single feeding of alfalfa hay may be lethal. So if you follow this blog and are fond of eating alfalfa, beware.

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