2013 March 16

While I’m all done with the moths from May 26, 2012, there was one thing that wasn’t a moth that was also on the wall (although it may or may not have been drawn to the light). It’s a pillbug, AKA roly-poly, AKA woodlouse, AKA potato bug . . .

I’ve posted these before, but it’s been a while. They are land-living crustaceans of the order Isopoda, which means that they have seven pairs of unspecialized legs that all look about the same.

These are all over the place around here, particularly in the spring. They are found in large quantities under rocks, in lumber piles, in basements, and in other places that trap a bit of moisture and have something organic for them to eat. My daughters love them, here are some more that Sam and Rosie caught for me in a bucket on May 21, 2011:

When we first moved out of town to this property in 1998, the dominant woodlice in our yard were the kinds that could not roll up. But, over the years, the population has shifted towards the ones like these, that can roll up completely into an almost perfectly spherical “pill”. They are Armadillidium vulgare, a formerly-European species that has become cosmopolitan due to its ability to live in basements. There is some color variation, with some having yellowish-brown markings while others are slate-gray. The one on top of the pile in this next picture appears to have been hollowed out, although it’s hard to tell whether it was a scavenger burrowing in (which would probably have been a cannibalistic nestmate) or something burrowing out.

Some of them looked like they had a harder time curling up than others. Like these two, which don’t seem to be able to “pill up” completely.

We can find them pretty much any time of year just by flipping over rocks, or looking around the yard in the morning when things are a bit moist from the morning dew.

Here are a couple more, from November 11, 2012, which are included mainly because I got them to “pill up” for photographs. This first one was a bit pale, it had probably just molted within the previous day or so and hadn’t fully darkened yet.

This next one was more typically colored, but it wouldn’t stay absolutely closed up long enough for a picture. Close, though.

The eyes are small, and barely visible. I think that the arrows in this next photo are pointing to the eyes.

The white patches on the underside, near the rear, indicate that this is a female.

Those are fluid-filled sacs where her eggs hatch out. Her babies stay inside these sacs, living in there as aquatic larvae until their first molt. The sacs then burst open, and the babies are born live as tiny little replicas of the adults. And, looking back at the earlier photo with one of the pillbugs being hollowed out, the hollow is right at the same place as these sacs. Which suggests that the earlier one may have been a female that had just recently given birth. I wonder how many times they can do it? Anyway, this works out well for them as far as being able to breed quickly. We clearly have more pillbugs than you can shake a stick at.

At any rate, they are all completely harmless detrivores. They don’t bite people; they don’t carry disease; they mostly don’t eat living plants and so aren’t significant agricultural pests (although they sometimes get into stored, moisture-rich vegetables like potatoes and squash); and they are a lot of fun for kids to play with.

Speaking of which, let’s see if I can upload this very old video that I shot of Sam playing with a woodlouse way back on November 29, 2007 when she was 2 years old (she is 7 now):

A girl and her woodlouse

(shortly after this was shot, she accidentally dropped it and it got away. “My woodlouse gone!” she cried. It was so sad. But I think the intervening 5 years has dulled the pain.)

7 Responses
  1. Steve Klaber permalink
    March 16, 2013

    Marvelous creatures, so like their ancient relatives the trilobites. Thanks for some neat pictures.

  2. March 16, 2013

    What a fun entry! Now I feel the need to go out and try to tell male from female pillbugs in the pile of them under the birdbath.

  3. March 16, 2013

    I love how she wants to give the little creature a kiss. Priceless.

  4. March 16, 2013

    As for the eyes, there’s probably no point in the creature being able to see. Find decaying plant material -> eat. Unexpected motion -> pill. Other pillbug -> mate. You wouldn’t even need to have decent sex-detection capabilities. If everyone else is following the same logic, sheer population density and random motion will put the little Elizabeth Taylors and Richard Burtons together and another generation will be on its way.

  5. katbird permalink
    March 16, 2013

    Just by coincidence I have found two woodlouse spiders (Dysdera crocata) in my house this winter. These large spiders with red legs eat sowbugs and pillbugs and have large jaws to piece their “shells.” I’ve kept them until a warmish day and let them go in the leaf litter.

  6. March 17, 2013

    I’ll keep a look out for the woodlouse spiders, but I don’t think they’re in the area yet. Once they get here, though, they’ll have plenty to eat.

  7. March 17, 2013

    One more thing. As we discovered from our Roly Poly experiment and the construction of Polytopia, the little guys breath through gills, so an additional bit of behavioral logic would be: moisture = good, dry = bad. That would help concentrate the polies, making mating more likely.

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