Insect Appreciation: The Oil Beetle

This is an oil beetle.  I was completely unfamiliar with oil beetles until I photographed this one in my garden a few weeks ago.  I finally got around to doing some research on it to find out what it was. I have a fairly reasonable knowledge of common garden insects, but this one was definitely new to me, and naturally, I had to learn about it.

It's a fairly large beetle that belongs to the Meloe genus of beetles.  This is the beetle on the tip of my gardening glove finger.  It had an iridescent blue colour, but if you look closely, you will see that it has exuded some greenish "goo" (scientific terminology there!) from a couple of its leg joints on the right side, and also its back end.

I was under the impression that this was an injured beetle that was leaking goo due to having been attacked by some other insect.  However, when I looked up the species, that's when I learned that oil beetles exude droplets of hemolymph (the insect equivalent of blood) from their joints when they are disturbed.  I had disturbed it by picking it up.  Good thing that I was wearing the gloves though, because that hemolymph contains cantharidin, which can cause severe skin blistering.  This is why this family of beetles also have the name of "blister beetles" in addition to the oil beetle name.

Livestock exposure to cantharidin (by inadvertent contact with or ingestion of the beetles) can be a serious problem requiring veterinary care, especially in horses.  If humans ingest it, a dose as low as 10 mg can actually be fatal!  Yikes!  Fortunately, I'm not in the habit of licking beetles.

I'm not 100% sure, but based on some further research I did, I believe this is Meloe impressus, since it is one of the more common oil beetle species in North America. I must say, I find its segmented antennae to be most interesting, and it has an unusual shape that is quite distinctive.

So now you know, if you find yourself interacting with an oil beetle, do not lick it.  Just a friendly public service announcement from yours truly.