Sunday, March 25, 2012

Blister Beetle

Short-winged Blister Beetle, a.k.a. "oil beetle," Meloe sp., on moss

Blister Beetle -- © Dave Spier

Here’s an insect worth knowing if only to avoid touching it. This Blister Beetle (Meloe sp., possibly angusticollis, or Short-winged Blister Beetle) is a member of the Family Meloidae (all blister beetles) and can exude a chemical from its leg joints that literally causes blisters on human skin. I moved this one out of the garden using a plastic plate and then "hit" on the idea of photographing it against a contrasting, green, mossy background.

I didn’t take time to measure it (and didn’t have a handy ruler anyway), but it seemed to be slightly less than an inch long. My Audubon field guide lists the Short-winged Blister Beetle as 5/8 inch or less, but this one seemed larger. There’s more than one species, and there’s a difference in the size of the two sexes. Males often have a bend in the antennae about midway along the 11 segments and this one seems to fit that description. However, in other photos I've seen of them mating, the male is shorter, assuming "he" is the one on top. I've never seen more than one at a time, so comparisons in the field are a little difficult. I therefore assume the kink in the males' antennae is more pronounced.

This blister beetle is dark steel-blue and has a finely pitted surface. The front wings (called elytra) cover part of the abdomen, but there are no hind wings and the beetle is unable to fly.

Adults can be found wandering about in spring and fall. They eat the leaves of vegetables and weeds. (I came across one reference to hundreds of these beetles eating chives.) Their eggs are laid near wild bee nests and the beetle larvae become parasites of the bees. Given the decline of honey bees due to Colony Collapse Disorder, I’d say we need all the wild bees we can get.

Meloe angusticollis is in the sub-family Meloinae and members of the genus Meloe are sometimes called "oil beetles." This is a good time to mention the website called BugGuide.Net ( You can track down any insect you find, and if not sure, you can submit a photo for possible identification. Registration is free.

If you have time to further research this insect, write to me at Corrections, comments and questions are always welcome at the same e-mail or connect through my Facebook page and photo page. There's also a community-type page for The Northeast Naturalist. Other nature and geology topics can be found on the parallel blogs Adirondack Naturalist and Heading Out.
More of my photos can be found on Picasa (Google+).


The Northeast Naturalist said...

from Michele Babcock-Nice via Linked-In • "As a teen, I had a female blister beetle in my entomology collection. I'm not sure if I still have it or not. I do still have many insects in my collection from my teen years. At any rate, I did pick up this blister beetle. I don't recall getting any blisters, however, she did defend herself from me by giving off her liquid. I also don't recall it being itchy or irritating at all, just odorous. I know that this beetle was a female because of her huge body that was very inflated in appearance. Very interesting. Thanks for posting."

The Northeast Naturalist said...

more comments via Linked-In:
Edward Saugstad • I've handled many blister beetles over the years, and have never experienced any skin blisters or other untoward effects. I think that as with many other arthropod-human interactions, there is a lot of individual variation as far as sensitivity is concerned.
Nancy Cohen Oderkirk • I've also handled many of these interesting beetles, which are apparently only deleterious once crushed. The larvae are predators of both bee and grasshopper (locust) eggs in the soil, so this complicates our assessment of them. I used to collect masses of them from my huge garden in Kansas. I'd get them to drop into plastic bags and freeze them... assuming that I'd leave enough of them in the field to keep the grasshoppers under control (along with the Nosema locustae that had been applied previously.)
A major concern seems to be feeding of beetle-infested hay to livestock. This should be avoided by feeding only hay that was baled early in the season, before the beetles emerged from the soil. Here's that reference:
Edward Saugstad • Thank you for posting that link, Nancy - the risk posed by the chemical (cantharidin) in blister beetles appears far greater for livestock than for humans, as we seldom ingest them!
Here's another relevant link: