Sow Bugs vs Pill Bugs

Don’t get ‘em mixed up!

Note the flared out segments of the sow bug on the left vs the more rounded body of the pill bug.

Some correction here from the earlier post thanks to feedback from an alert reader. Thanks, Victoria! With their similar appearances Sow Bugs and “Roly Polys” are often mistaken as the same species. Although both are crustaceans related to crabs and crayfish, there are distinct differences upon close inspection. But if you don’t happen to have a magnifying glass or macro lens handy one particular behavior will distinguish them. “Roly Polys” or Pill Bugs, Armadillium vulgare, roll up into a ball when frightened. Sow bugs, Oniscus aselus, do not display this behavior. Sow bugs also have a more armored carapace that is slightly flattened out at the edges. They do have a some other similarities, though. Both breathe through modified gills, both feed on decaying plant and animal material, and both are European imports. Those modified gills, by the way, do not do well in dry conditions. And in case you ever wondered what they look like under there – now you know!

References:

“Bugs of Washington” by John Acorn

“Invertebrate Zoology” Rupert and Barnes, 6th edition