Case-Bearing Beetle Larva

2023 August 20

Sandy bought some locally-grown strawberries at a roadside stand on July 10, 2023. When she got them home, she and the girls were cleaning them, and found this tiny object that appeared to be some kind of pupa, so they kept it for me.

It was pretty tiny, about half the size of an uncooked rice grain, and hard to see details until I got out the macro camera to have a closer look. Which was when we found out that it was hollow, but not . . . quite . . . empty.

If you look in the opening, you can see what look like legs. So I waited a bit, and after a few minutes whatever was inside did, in fact, stick its legs out.

It then proceeded to slowly trundle about on the paper that I had put it on for photography.

That was as far as it ever came out, and at the slightest disturbance it would pull back up inside of its case, so the legs were all that we ever saw.

So at first I thought it was a bagworm, which are a group of moths where the larvae build a shell for themselves out of debris. But they all have characteristic ways of building their shells, and none of them built anything quite like this. For a brief moment I thought maybe it was some sort of land-dwelling caddisfly, which also build shells kind of like this, but they all have aquatic larvae. So, that meant it was some third kind of thing.

And on further searching, it looks like that third thing is most likely one of the Case-Bearing Leaf Beetles, subfamily Cryptocedphalinae. More specifically, I think it is most likely one of the Warty Leaf Beetles, tribe Fulcidacini.

It turns out that the case is made of their feces, sometimes with some miscellaneous plant matter mixed in for bulk. And the goal of the case is not so much to give them mechanical protection from predators, as to camouflage them. And the thing they are camouflaged as, is caterpillar droppings. So, basically they are using their own poop, to disguise themselves as some other insect’s poop.

These are probably insanely common, but are hardly ever noticed because they frankly don’t look like anything that one would want to examine too closely. The larvae are apparently pretty opportunistic, eating most types of debris and occasionally green leaves or fruit. Which obviously includes strawberries. They are so tiny, and so unfocused in their eating habits, that I wouldn’t consider them an agricultural pest or anything. They are just one of the myriads of tiny insects that are just sort of around.

I missed a couple of weeks of postings for a few reasons, not least of which that our home internet connection had gotten flaky and unreliable to the point where it was nearly useless. The problem was that we have a radio-link connection to our internet provider that needs a clear line-of-sight. Which we had when the system was installed, but over the years a basswood tree had grown up until it finally got tall enough and dense enough to block the signal. But last week we had the tree removed, and our internet now works fine, or at least as fine as it ever did. At least the tree was on our property, so we could do something about it.

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