Oil Beetle from Canada

Subject:  Large bluish beauty
Geographic location of the bug:  Outside Sackville, New Brunswick, Canada.
Date: 08/27/2018
Time: 11:38 AM EDT
Your letter to the bugman:  Walking near my parents’ trailer, I nearly stepped on this rather beautiful creature and couldn’t help but wonder what it is. It was generally inclined to stay still, but once I put it down, after lifting it for closer inspection, it was happy to race over very course gravel in order to get back to the tall grass.
How you want your letter signed:  Parker

Oil Beetle

Dear Parker,
This is a Blister Beetle in the genus
Meloe, commonly called an Oil Beetle because the iridescent surface of the beetle looks like oil on water.  Blister Beetles should be handled with caution, as many species are able to exude a compound called cantharidin that is known to cause blistering upon contact, especially in sensitive individuals.  The “crook” in the antennae indicates this is a male Oil Beetle.

Oil Beetle
Oh, my, thank you for the caution! It’s easy for me to forget about bugs (other than mosquitoes) presenting danger while vacationing up here. (Especially after an event a month or two ago where I helped a parent mud dauber rescue its young from a nest it had built on an RV. Didn’t want to bring the larvae to an inappropriate habitat.) I’ll be sure to observe from an appropriate distance from this point on.
Thank you again for your knowledge! It not only satisfied my curiosity, but also sparked some good discussions with my family.
Follow-up Questions:  I was wondering if I could get you to impart yet more knowledge; as I was cutting the grass, a saw some more of the oil beetles and developed a two general follow-up questions about the oil beetles. (Unfortunately I’d left my phone inside, so no pictures.)
First, on the pragmatic side, I believe there were several of the beetles this time, some with crooked antennae and some less so – I figure, then, that those are males and females. Do these beetles have any nesting or mating behaviors worth noting? They seemed to be congregating under my parents’ “laundry shed” (for lack of a better term – it’s a reused ocean container set on concrete blocks.) I ask because, while I assume the beetles are not aggressive towards humans from the nature of their defenses and my (very limited) observation, if they are going to be making a home there I want to make sure my dad doesn’t get blistered while doing maintenance.
My second question is out of curiosity more than anything else; I wonder how much is known about the oil beetle’s role in its ecosystem. We hadn’t seen any on previous visits up here, but now we’ve had several (my dad had seen one before me but mistook it for a large ant.) Might their presence have increased due to the land being slowly developed (i.e. addition of gravel and an ocean container and/or shorter grass)? I also got curious when I saw one beetle cross inches in front of a spider that seemed to be on a web. Admittedly, it was not a particularly strong-looking spider. I suppose I could have just mistaken a harvestman, really. Nonetheless, with their toxins, does much of anything eat them? Or do the oil beetles eat any kind of pest?
While I do get very curious about these things, I understand that you are busy and probably want to prioritize others’ questions. Thank you for all you do! It’s a great service to the world.
Hi again Parker,
Blister Beetles as a family tend to have complex life cycles.  Of the genus
Meloe, the Oil Beetles, BugGuide states:  “Larvae feed on eggs and other food in bees’ nests” and “In some species, triungulins [see definition below] aggregate and use chemical signals to attract male bees to which they attach themselves. This allows transport (and transfer) to a female bee who carries them back to her nest (Saul-Gershenz & Millar 2006).  First-instar larvae climb to the top of a plant as a group, clump together in the shape of a female solitary ground bee, exude a scent imitating the female bee pheromone. When a male bee comes and tries to mate with the clump of larvae, some of these clamp onto his hairs and eventually get to female bees when he mates for real. Impregnated female bees fly off and build nests in burrows; triungulins move to the new nests and feed on honey and pollen stocked by the bee for her own young. –Jim McClarin’s comment.”  Of the family, BugGuide notes:  “Life cycle is hypermetamorphic. Larvae are parasitoids. Eggs are laid in batches in soil near nests of hosts, sometimes in nest of bee host, or on stems, foliage, or flowers. Larvae undergo hypermetamorphosis–first instar larvae (usually called triungulins) are active, have well-developed legs and antennae. These typically search for hosts. Later instars tend to have reduced legs and be less active, having found hosts. There is a coarctate (pseudopupal) stage, which is usually how the larvae overwinter. Life cycle may be as short as 30 days, or as long as three years. It is typically one year, corresponding to that of host.

Triungulins of some meloids, e.g. in Meloe, aggregate and attract male bees with chemical signals (Saul-Gershenz & Millar 2006).”
Absolutely fascinating! Nature really is amazing. Thank you again so much!

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