Carrion(?) beetle larva, unidentified eggs

2007 June 23

A few weeks ago, I posted pictures of a predatory beetle, and mentioned that I’d like to get a picture of the larva of that beetle, because they were pretty wicked-looking[1]. Well, here’s a nice example, which I found crawling across the kitchen floor[2]. Correction: this is evidently some type of carrion beetle (see comment from “Anthony” below). The small squares on the grid are 1 mm, so this larva is close to 2 cm long.



So, anyway, I’m pretty sure that this is a Calosoma beetle larva, probably the same species as the beetle I talked about in this post. One thing I’m noticing is that the mandibles are much less developed in the larva, which makes sense. While it is pretty frisky for a larva, those short legs mean that it can’t run down and pounce on prey like the adults can, so it is probably restricted to grabbing little things that it finds in the leaf litter.

While the Calosoma larvae do look similar to this one, the larva of, say, the American Carrion Beetle, Necrophila americana, looks darned near identical, and I have to agree that this is a strong candidate. Especially since I see the adult carrion beetles of this species very frequently whenever we find dead animals lying about.

Except . . . this larva was not found anywhere near carrion, and we constantly find them scurrying about as free-roaming individuals, with not a corpse in sight. We usually see three or four of them every year crossing the driveway. And they are very frisky for a larva, and act like a free-roaming carnivore. The guide page for Necrophila americana says that the larvae stay with the carcass, and burrow into the soil to pupate right next to it. So why are we so often finding these roaming free? I dunno. Maybe their lifestyle isn’t as well understood as it should be? Or maybe they used up their piece of carrion before they finished growing, and so are roaming around looking for something else?

I guess, next time we find one, I need to try rearing it to confirm once and for all what it grows up into. It should be easy enough, just give it both a piece of rotting flesh and a couple of insect grubs, keep giving it whichever one it goes for, and then let nature take its course and see what comes out of the pupa. Anyway, here is a bonus picture that is never going to get identified enough to warrant an entry all of its own:


These eggs were laid as a close-packed sheet on the outside of our kitchen window sometime around May 1, and hatched out about two weeks later. The individual eggs were pretty small, about half a millimeter or so, and you can still see the white circles that are all that are left of the egg capsules. I expect that these are some sort of moth caterpillar, but I wouldn’t presume to try to narrow it down much more than that. They took almost a day to either disperse or get eaten, and since they were on a window, their food plant is unknown.

[1] Specifically, I said that it looked like something Kahn might put into Chekov’s ear in a certain movie.

[2] By this time, you probably think that my house is a festering pesthole, riddled with vermin. I’ll grant that it isn’t one of these sparkling, sanitary places, but it isn’t as bad as all that. I think it’s just that I’m specifically looking for insects these days, and this is one of those “seek and ye shall find” sorts of situations. Actually, I think it would be cool if a lot of people started cataloging the arthropods in their houses, it is a distinct, thriving environment and probably has a lot of species that aren’t really found in the wild any more. An interesting point that I read a long time ago is that, for an insect, the house environment closely resembles a desert (due to the lack of water), with occasional oasises (sinks and showers/bathtubs), but without the wide temperature swings. We should therefore expect most of the household fauna to be derived from desert animals, and not necessarily from the animals that naturally live outside our houses.

[3] For all I know, it may be a lot more closely related than just “the same species”, considering that they were both found in the same general area. It might be, say, a second cousin once removed. Or even a first cousin. Considering the lifespan of these beetles (about 3 years), it could potentially even be a half-sibling or an offspring.

4 Responses
  1. Anthony permalink
    March 6, 2008

    That is not a catterpillar hunter beetle larva, it is the larva of a carrion beetle. This is a picture of another larva:

    These are pictures of possible species (there is more than one):

  2. March 7, 2008

    I’ve changed the entry, thanks for the correction! The picture you point to certainly does look more like this specimen than the few pictures of the various Calosoma larvae on BugGuide. I’m still puzzled about its lifestyle though – we regularly find these crawling across our driveway, with no nearby carrion sources. BugGuide says that the larvae stay with the carrion until they pupate, so why are so many of them around here wandering like that?

  3. Rachel permalink
    August 23, 2008

    We have those same larvae on our window – just hatched today. Did you ever hear what they were?

  4. August 23, 2008

    No, aside from probably being some sort of moth. There’s probably a few hundred species of moth that lay eggs like that, and it could have been any of them. The only real way to identify them would be to catch them, luck out on finding their food plant, and raise them up to large enough that they start showing distinctive features. I didn’t manage to do any of that, so we will just never know for sure what they were.

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