Bee Rider

Two weeks ago I was driving past a spot where I knew there was a population of rare orchids that blooms in early June, so I stopped by to have a look.  I found a few of them, and the flowers had mostly gone by, but this one was still pretty photogenic:

Arethusa bulbosa, listed as Threatened in Massachusetts.

After taking several shots of this flower, I took a closer look to see if any potential pollinators were visiting it.  I noticed a tiny brown insect, which I thought might be a thrips, moving around on the flower’s lip.  See it?  It’s looking directly at the camera.  Not really captured well by the Nikon 18-55 mm lens, so I got out the Canon 65 mm macro for a better view of the bug.

A Meloe larva (1.4 mm) waiting inside an arethusa flower.

I was pretty sure it was a newly hatched larva, called a triangulin, of a blister beetle (Meloidae), and Vassili Belov just now confirmed that it is one, in the genus Meloe, after checking with blister beetle specialist J. D. Pinto.  I guessed what it was not because I had any idea what a baby blister beetle looks like, but because of what it was doing.  Certain blister beetle larvae hatch from eggs laid on vegetation, then climb to flowers where they wait for a solitary bee to grab onto.  A successful triangulin rides a bee back to its nest, where it eats the pollen and nectar provisions, often along with the bee larva for which the provisions were intended.  As it grows, the beetle larva develops from the lean, leggy triangulin into a fat, almost legless grub, as shown here.

According to every source I’ve checked, blister beetles in the genus Meloe are known as “oil beetles” because when disturbed, they exude an oily substance from their leg joints that causes human skin to blister.  I believe this is true of all blister beetles (hence the name, “blister beetles”), so I’m not sure why just this genus is given that name.  I had always assumed it was because the adults are iridescent like an oil slick.  They look something like enormous, bluish ants, and it is not uncommon to find them wandering through lawns or munching on vegetation.

An adult female oil beetle (Meloe impressus) clambors across a lawn.

(Added 2/16/2012:) I just found this amazing video showing the different strategy used by Meloe franciscanus triangulins to get a ride on a bee. There is an explanation here of what’s going on in that video.

About Charley Eiseman

I am a freelance naturalist, endlessly fascinated by the interconnections of all the living and nonliving things around me. I am the lead author of Tracks & Sign of Insects and Other Invertebrates (Stackpole Books, 2010), and continue to collect photographs and information on this subject. These days I am especially drawn to galls, leaf mines, and other plant-insect interactions.
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3 Responses to Bee Rider

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