Pill Beetle

2011 August 20

Sam found this one walking across our sidewalk in front of the house on May 21, 2011. It was almost 1 cm long, slow-moving, heavily-armored, and would tuck itself into a neat little ball when disturbed.

I thought at first it was some kind of scarab beetle, but scarab beetles have complex antennae that split into multiple “fingers” at the tips, while this one had simple, “beaded” antennae.

In this next picture, you can see how it could tuck its head completely under its body. When it also pulled in its legs, it formed a little armored “pill” that would be fairly hard to eat.

It turns out that it is actually a Pill Beetle (family Byrrhidae). Further, v belov on BugGuide says it is in the genus Byrrhus, but that determining the exact species would require examining the male genitalia.

Beetles in this family evidently mostly eat moss, lichen, liverworts, and sometimes grass roots, and therefore are commonly found in moist areas and on/under rocks. They aren’t rare (I found another one a few days after Sam caught this one), but they aren’t common enough to be any sort of pest, either. I think it’s interesting that they live in similar environments to pillbugs, and have converged onto pretty much an identical defensive strategy – roll up into a little armored ball. This suggests that the main predators in that environment are probably things small enough to be deterred by armor, like centipedes.

5 Responses
  1. August 21, 2011

    Does their armor grow with them over their lifetime?

  2. August 21, 2011

    I was thinking, Why would this deter a bird when hard-coated seeds don’t? And then I realized that few birds go around shoving their beaks under rocks!

  3. August 22, 2011

    KT: It looks like at least some of the Byrrhidae larvae are armored, kind of like woodlice or pillbugs. Like these, for example. They have to shed their skins periodically, like all other insects do, so the armor is periodically replaced as they get older.

    Anne: Yep. It’s all a question of who you are defending against. If it’s a bird, you need things like camouflage, speed, painful spines, or a bad taste. If it’s a spider or a centipede, on the other hand, it is quite possible that those things aren’t all that helpful, and you are better off with armor thick enough that their fangs can’t penetrate. And the defense doesn’t have to be perfect in order to be selected for, it just has to be better than not having it.

  4. loli permalink
    November 29, 2012

    hey,i hv a question here..
    is there a bettle/bug that sucked human blood ? or any kinds of blood..
    i’ve found this ‘bettle’ (i don’t know if it is a bettle )
    it has round-shape,like coffee bean structure,grey in colour
    and it attached to my brother’s arms..at first we thought it was harmless piece of skin but once its separated naturally from my brother, it has this hairy feet comes out..
    as for that,my brother kept it in a plastic 4 us to searched wht is that thing , but accidently my sister step on it,,
    and you know what happen ?
    it burst out ! pop ! and likely large amount of blood in that piece of plastic .like linches being press out..and i keen to know what is it..
    if u hv any answer,do e-mail me ,,thanks..

  5. November 29, 2012

    Loli: It sounds like your brother had a tick. I’ve got more information on ticks here:


Comments are closed.