European Sowbug

2015 October 3

I found this crawling on the wall near our front door on June 23, 2015. And while this is a species that I photographed before, that was way back in 2007, and the previous pictures are not too good. So I says to myself, I says, “Self, you need to re-photograph this one.” So here it is.

It’s a European Sowbug, Oniscus asellus. Last time I’d misidentified them as being the common rough woodlouse (Porcellio scaber), but those are more of a slate-gray color (and I’m not entirely sure that they live around here yet in any case).

As you might guess from the name, they came over from Europe and rapidly colonized most of North America, mainly by riding around on things when people ship them from place to place. Back when I was a kid downstate, these were the dominant isopod crustaceans that we’d find under logs and rocks. And up here around Houghton, they were the dominant species at the time we bought our place outside of town. But, even at that time, we were starting to see a fair number of the true pillbugs (Armadillidium) another European import that evidently came over later. And in the past few years, the pillbugs have almost completely displaced the sowbugs, to the point where finding this one was actually getting to be an unusual sight.

Speaking of sight, woodlice are crustaceans, and crustaceans (like insects) have compound eyes. However, when we look at this one’s eyes, we see that they aren’t quite like an insect’s eyes – the facets are not so tightly squeezed together, and more like a bunch of discrete eyes that happen to be close to each other than a fully integrated eye.

If we look at the underside, you can see that there are plates on the bottom that cover gills, particularly near the rear. These land-living crustaceans don’t have lungs, and so they have to live in moist areas where their gills can absorb oxygen from the air without drying out.

You’ll find these a lot in gardens, but mostly they only eat dead and rotting things, so your vegetables are mostly safe. Although, if you leave (for example) a melon in the garden too long, and the part where it rests on the ground starts to rot a little, the sowbugs can start eating the rotting part, making it look like they are actually eating the melon directly.

3 Responses
  1. October 3, 2015

    They also like dog scat. So there’s that.

  2. Carole permalink
    October 3, 2015

    Photos you can be proud of. Great one of the eyes.

  3. Tim permalink
    October 5, 2015

    At certain times of the year, when the females are plump with fully formed offspring, handling them can cause the babies to erupt from the chest. One of the creepiest things I’ve ever experienced.

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