Tiny scavenging beetle (and a little something extra)

2015 August 12

On May 23, 2015, Sandy was working in her garden and found a dead woodlouse that had these tiny little beetles inside. You can see part of the woodlouse in the upper left side of the picture. The beetle we can see was only about 2 millimeters long.

The beetle was on its back because it was in a tussle with some kind of extremely tiny creature that was invisible to the naked eye, and I could only see it through the camera. At first glance it appears to have a pair of legs on each body segment (which would make it some sort of myriapod). But looking more closely, those might be hairs, not legs, in which case it is most likely some kind of grub.

Anyway, there was more than one beetle, here’s one that could flip over for a dorsal view. He’s all black except for brown tips on the wing covers.

Given what these beetles were doing (eating a dead, dried-up arthropod), I thought at first they might be some relative of the Dermestid Beetles. But, the dermestids all seem to have a differently-shaped pronotum (the plate between the head and the wing covers), and an extra little plate where the wing covers come together that these here completely lack. The antennae don’t look right, either. Well, I guess this one is a candidate for asking about on BugGuide . . .

[thirty seconds after posting to BugGuide]

Wow, that was fast! I barely had time to get these entered before they got identified as “water scavenger beetles” in the subgenus Cercyon! It turns out that not all water scavenger beetles live in the water, a lot of them are tiny terrestrial scavengers. Like these.

Also, at least one person on BugGuide thinks that the white, hairy thing the first beetle is wrestling with could possibly be the larva of one of the Forcipomyia biting midges, also known as “no-see-ums”. Which we certainly have around, so this is actually fairly likely. It isn’t clear whether the midge larva was attacking the beetle for food (some midges have parasitic or carnivorous larvae), or if they just happened to get accidentally stuck together.

The beetles really get to travel, people accidentally carry them all over the place. There are at least 16 species in North America that have been carried here from Eurasia, and given how small and hard to see they are, probably more. So I’m going to mark these as “non-native”, because they probably are.

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