Rove Beetle

2008 October 4

S. found this one climbing the wall of the garage. Despite appearances, it is not related to earwigs. It’s actually a beetle[1]. No, really!

It looks like a Rove Beetle, probably in the subfamily Staphylininae. It might be one of the species in the genus Ocypus, but I’m leaning more towards the genus Tasgius.

You might notice that it is looking a bit dusty. That isn’t actually the way it looked when we found it, it was actually glossy black. Unfortunately, it died almost immediately when it was refrigerated, and quickly started picking up dust and debris. It would have been better to photograph it alive, but these guys are fast, slippery, and hard to get to stay still.

At first, I thought that the red speck on its side might be a young velvet mite during its parasitic phase. But, closer examination shows that it is probably something like a paint fleck, it doesn’t look symmetrical enough to be a mite. The color is right, though.

So, if this is a beetle, why does it look so much like an earwig without the forceps? I think this is another case of convergent evolution. The earwig has a shape that is well-suited for its lifestyle, crawling around under rocks, dead leaves, and other debris to scavenge whatever food scraps they can find. These beetles have adopted the same lifestyle (I frequently find them under rocks and logs), and so they are converging on the same shape.

Something I’ve noticed is that they also have a defensive posture very similar to earwigs – when they feel threatened, they point their abdomens straight up in the air. Earwigs do this because it brings up their forceps, so that they can pinch whatever is after them. The rove beetles don’t have forceps, though, so they must have some other reason for doing it. I’m thinking that they may have some sort of defensive chemical spray, although if they do, it isn’t anything that I can smell, or that is sufficiently caustic to affect my skin. It is possible that they don’t have any defensive chemical at all, and this might be yet another case of mimicry (only this time, mimicking an action instead of an appearance). It could be that there are enough small insects that do have a defensive spray, that when a predator sees an insect point its abdomen like that, it assumes that this one has a spray too, and so leaves it alone.

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[1] It occurs to me that, for the last four weeks, we’ve had either pictures of beetles that look like other things (bumblebees, moths, and now earwigs), or other things that look like beetles (a seed bug nymph). There’s a lot of mimicry and convergent evolution going on in the world of beetles.

2 Responses
  1. October 5, 2008

    Very cool! Don’t think I’ve seen one before.

  2. brenda beebe permalink
    October 28, 2008

    Hey–Here in California I have just come across some of these odd looking beetles in my backyard. I finally got them identified through our local AG dept.! I had never encountered them before.
    I’m glad the are beneficial critters. I have photos of mine–different than the one posted here though I’ve seen them both in a line-up showing them as all variations of same.
    The ones we have in our backyard are large (1 1/4″long x 1/4″wide) and mat black with wings. I found them deep underground while weeding out clumps of rye grass, and then again while digging a hole to plant a bamboo root ball.
    brenda

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