A rather common resident in our compost bins, the sowbug (Porcellionides pruinosus) is a terrestrial crustacean in the order Isopoda. A sort of woodlouse, the sowbug is related to another common crustacean: the pillbug, or roly-poly. The sowbug differs from its cousin, though, in several ways. It cannot roll into a ball and is flatter and faster. It also needs a moister environment and so isn't seen out in the open very often, instead remaining under the cover of rocks and logs. Sowbugs are scavengers, and I have seen them eating dead insects, plant matter and mammal droppings. They breathe with gills, which are enclosed in a compartment on their underside. Even though they must avoid conditions that are too dry, if they are immersed in water, they will drown.
This is not the only species of sowbug in our area, but it is recognizable by the pruinose, or bluish waxy coating (makes it looks sort of dusty), that provides its species name.