Toxic Bee-Killing Hitchhiker Beetles (I Know, Right?)

I’ve said many times that I’m no entomologist.  I am an invertebrate enthusiast.  I enjoy photographing small things, which means I end up with a lot of images of tiny invertebrates.  Once I have photos, I love to figure out what it is I’ve photographed and how it fits into the incredible complexity of its ecosystem.  The only times I’m ever disappointed by that research is when I can’t find any good information – often because there just isn’t much known about whatever creature I’m looking up.  When I can track down a story, it is always fascinating, and reinforces my sense of wonder about the world.

The latest example of that came last week while I was photographing pasque flowers at the Niobrara Valley Preserve.  I noticed a few bees and other insects hanging around the flowers, but most were too wary to be photographed – with one big exception.  There were several big black beetles with large bulbous abdomens and short wings feeding on pasque flowers.  They were intent enough on feeding that I was able to get a few decent photographs, and promised myself I’d look up the species later.  Before I had a chance to start doing research, former Hubbard Fellow Jasmine Cutter texted me some photos of what looked like the same kind of beetle feeding on pasque flowers up in North Dakota and asked if I knew what they were.  Nope, but I was going to.

An oil beetle feeding on pasque flower at the Niobrara Valley Preserve last week.

After a rare failed attempt to use, I sent photos to a couple friends and James Trager responded quickly with the answer – oil beetle (Meloe sp.), a kind of blister beetle.  Once I started looking for more information, I was shocked that I’d not come across oil beetles before.  Ok, not shocked, exactly, since there are way more great insect stories out there than I’ll ever learn, but still surprised, given the abundance of oil beetle accounts online.  Of those, I particularly recommend Piotr Naskrecki’s The Smaller Majority blog, as well as Adrian Thysse’s Splendour Awaits site.

So, what did I learn? First of all, oil beetles produce the same kind of toxin as all other blister beetles – a compound called cantharidin.  Ingesting only a small amount of cantharidin is toxic to most vertebrates.  While that seems like a great way for an oil beetle to get revenge on anything that eats it, it doesn’t necessarily prevent the big flightless beetle from being attacked and killed in the first place.  Don’t worry – there’s more.  When an oil beetle feels threatened, it can secrete bright yellow hemolymph (the insect equivalent of blood) from its leg joints.  As one does.  That hemolymph contains enough cantharidin that any contact with the skin of potential predators causes painful swelling and blisters.  That, of course, is a pretty good deterrent against predators, as well as any foolhardy humans trying to manhandle an oil beetle.

As a side note, cantharidin has been long recognized by humans as a powerful chemical.  Despite its extreme toxicity, it has actually been used (in very small doses) as an aphrodisiac, starting at least a thousand years ago.  Because of the severe consequences of even a slight overdose, however, there are gruesome stories of hopeful lovers causing very painful deaths to themselves or others.  Cantharidin also has a long and varied history in medicines.  Currently, it is being tested for its effectiveness at treating cancer (as in this recent example).

The wings of oil beetles are much too small carry their weight.

The ability to secrete toxic bright yellow fluid from its leg joints is a pretty good story.  However, that just scratches the surface of the fascinating natural history of oil beetles. Most beetles mature through a process called complete metamorphosis, in which larvae  hatch out of eggs and grow until they pupate and become adults.  The larvae usually look completely different from the adult, and often have a very different lifestyle as well.  Oil beetles, however, go above and beyond by using a process called hypermetamorphosis.

When an oil beetle egg hatches, what crawls out is called a triungulin, a speedy little creature that looks much like a tiny silverfish.  The triungulin cluster together and emit a chemical that mimics the pheromone of female solitary bees (bees that individually make nests and raise young, as opposed to honey bees and other social bee species).  A male bee, upon catching the scent, will descend upon the mass of triungulin and attempt to mate with it (guys are so dumb when they’re horny).  Instead, the triungulin quickly crawl up onto the bee and hold on tight.  They stay with the male bee until it finds a genuine female bee and mates with her, at which time the triungulin scramble aboard the female.

Once onboard the female bee, the triungulin hitchhike back to her nest burrow.  When they arrive, they detach themselves and start eating everything then can find in the nest, including the bee eggs and larvae, along with the food the mother bee provisioned for them.  You can watch an incredible short video of oil beetle triungulin here.  During their time in the host bee’s nest, the triungulin molt into much more traditional grub-like larvae, and eventually pupate and turn into adults.  As adults, oil beetles feed on vegetation – including, apparently, pasque flower blossoms.

You’d never know by looking at its cute face that this oil beetle spent its childhood eating baby bees.

Do you see what I mean about the fascinating lives of invertebrates?  Who would’ve guessed that a bulbous-butt flightless beetle would have such a great story?  Answer: anyone who knows much about invertebrates.  As I write this, I have my booted broken ankle propped up awkwardly on the couch, but I’m already formulating plans for how I’m soon going to (carefully) drag myself out into the prairie to collect more images and stories of tiny little creatures.  Stay tuned.

Photo of the Week – July 1, 2016

I often tell people, “I’m not an insect expert, I’m an insect enthusiast.”  I don’t spend nearly enough time immersed in the vagaries of invertebrate taxonomy and biology to know much more than some interesting trivia about most species.  This week provided a couple great examples of my lack of expertise.

Early in the week, I was at the Niobrara Valley Preserve.  While walking one morning, I noticed a longhorn beetle on a white prairie clover flower.  I felt pretty good about recognizing it as a longhorn beetle, and was even able to remember part of the genus (“Typo something, I think”).  I also noticed a small weevil on the same flower.   “Cool!”


Longhorn beetle (Typocerus confluens or Typocerus octonotatus) and a weevil on white prairie clover (Dalea candida) at The Nature Conservancy’s Niobrara Valley Preserve.

A few steps away, I saw another white prairie clover flower, and sure enough, there was a longhorn beetle on that one too.  And another weevil.  This second longhorn beetle had a different pattern on its back from the first one, so I assumed it was a second species.  “Nice,” I thought, there’s a good example of insect diversity – two different beetle species feeding on the same flower.


Another longhorn beetle on another white prairie clover flower.

A few steps away from that second flower was a third one, and it had a longhorn beetle on it as well.  The third beetle looked different than both the first and the second ones.  (Oh, and there was a weevil on the third flower too.)


A third longhorn beetle.

As I walked away from the white prairie clover patch, I started composing a blog post in my head about insect diversity.  Something about how important it is to have lots of different species within each group of animals so that if one species suffers from a disease or some other malady, there are others that can cover the role it plays in the natural world.  Blah blah blah.

When I got back to WiFi, I emailed my longhorn beetle photos to Ted MacRae (an ACTUAL insect expert) who is generous enough to help me with identification of beetle photos.  (Check out his fantastic blog here.)  I asked him what species these three beetles were so I could name them in my upcoming blog post.  When I got his reply, my blog post idea went out the window.  They weren’t three different species at all – they were all the same one!  (By the way, Ted couldn’t tell for sure from my photos which of two possible species they were.  He said he’d need to see the “last ventral abdominal segment” of each to be sure.)

Now, how is an insect enthusiast supposed to keep up when three beetles of the same species don’t even have the common courtesy to look like each other??   I’m ok with the occasional oddball.  With flowers, for example, it’s not uncommon to see one white flower out of a big patch of purple spiderwort or vervain flowers.  Fine.  Genetics provides a few quirks now and then.  But I only saw three longhorn beetles, and none of them had the same color pattern on their back??  I give up.

Oh, and the weevils?  Don’t even ask.  I don’t know.  They all look the same to my eye, but what does that mean?  They’re probably three different species that just happen to be feeding on the same flower.  That would be about right.  Geesh.

So then yesterday, I was in our Platte River Prairies and noticed a crab spider on a black-eyed Susan flower.  It was a pretty spider (you have to admit that) so I stopped and photographed it.

crab spider

Crab spider on black-eyed Susan flower.  The Nature Conservancy’s Platte River Prairies.

After I photographed the spider, I gave the other flowers nearby a quick look, and sure enough – there were crab spiders on several of those too.  Now, here’s the thing: the other crab spiders might have been different species, or they might not.  I’m not even going to guess.  They had different patterns on their abdomens but were generally the same color.  The first one was much broader, but that’s likely because she’s a female, and that’s how it works with spiders.  The other two might be different species or they could be from different growth stages and the patterns might be different for that reason.  Or, apparently, THEY COULD JUST LOOK DIFFERENT FROM EACH OTHER FOR NO PARTICULAR REASON OTHER THAN TO BE CONFUSING.

crab spider

Another crab spider.  


One more crab spider

I could email photos of the crab spiders to a friend who occasionally identifies them for me, but I’m not going to.  I’m choosing instead to simply admire the aesthetics of these fascinating little creatures, and appreciate some general trivia about crab spiders (for example, their front two sets of legs are extra long for capturing ambushed prey, and some species of crab spiders can change color to match the flower they sit on).  After all, I’m an insect enthusiast, not an insect expert (or a spider expert).  So there.