Blister Beetles’ Defense Mechanism
Blister beetles are aptly named, for when they are disturbed they emit a yellow, oily, defensive secretion (cantharidin) from their joints which usually causes blisters when it comes in contact with skin. This toxin deters many potential predators and is especially effective against ants. According to naturalist/forester/writer Ginny Barlow, as little as 100 milligrams is reported to be fatal to humans if ingested, and this amount can be extracted from just a few beetles. Humans used to crush and dry blister beetles and use the resulting concoction for gout and arthritis. It was also used as a popular aphrodisiac known as Spanish fly. Because of its toxicity, it is no longer widely used in medicine.
Cantharidin is, however, indirectly used by tree-nesting nuthatches. With a limited number of tree cavities, there is competition among animals using them to raise their young, especially between squirrels and nuthatches. Nuthatches have been seen with Short-winged Blister Beetles (Meloe angusticollis, see photo) in their beaks, “sweeping” them on the bark around tree cavity entrances. The nuthatches don’t eat the beetles, they strictly use them as tools. It is assumed that the birds do this in order to repel squirrels with the cantharidin that is smeared on the tree. (Thanks to Ginny Barlow for photo opportunity.)
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Naturally Curious with Mary Holland 
Oh my goodness.Yet more (in a never-ending string of) remarkable bits of information! Wow. How did they learn that?? Is it instinctive, somehow, or modeled/taught/observed? (I wonder if the blister beetle is released more-or-less intact and able to go on its merry way, after this process…
October 5, 2015 at 8:43 am
Absolutely amazing nuthatch behavior. I’m wondering how that could have evolved. Almost (but not quite) makes me consider the possibility of an Intelligent Designer.
October 5, 2015 at 3:41 pm
I know the “Blister Beetle” Juice is used as a medicine topically as we had our dermatologist use this on my son for getting rid of numerous warts that were on the bottom of his feet. It didn’t hurt to apply but we needed narcotics later that night to deal with the pain and swelling (it did indeed blister his whole foot- was alarming) and he couldn’t walk on his feet for a few days he hobbled. It was Impressive response but it worked. The dermatologist explained he had to order this medication from out of the country to use in the office as it was not FDA approved. I’m a pediatrician and have seen kids not tolerate the other modes of treatment that are painful so the blister beetle procedure didn’t hurt at all and he was fine tolerating this application it was just the delayed (hours later effect that he was miserable for). Just saying that in special situations it can be used to help people as it cured my sons wart troubles.
October 6, 2015 at 11:49 am
Hi Caroline,
Thanks so much for sharing your son’s story. I was aware that it is used for some skin conditions – impressive that it worked on warts! I am surprised it wasn’t available in this country, actually. I have a friend who thought she’d test it out on her skin, and applied some to it – for whatever reason, she got no reaction so I tried it when I found a beetle yesterday and had a similar non-reaction. Admittedly, it was a minute drop that I applied!
October 6, 2015 at 1:13 pm