|Photo by Cletus Lee|
Okay, this is clearly a trick question, so you've probably rejected the ladybug. And you'd be wise to do so: a ladybug is an insect, which has six legs. A pillbug has fourteen.
You're not going to go with kangaroo either, since you know that's a mammal. Correct again. But do give the pillbug credit for its similarity to kangaroos and other marsupials: like them, the females have special pouches to hold their young.
So, yes, that leaves the lobster as long-lost relation to the pillbug; they are both crustaceans. (Shoulda known I couldn't get one past you!) Having long ago evolved from the briny deep, pillbugs retain gill-like breathing apparatus that requires moisture, which is why you'll likely find them in damp places.
A pillbug can be differentiated from its close relation, the sowbug, by its ability to roll up in a ball--sowbugs can't manage this--and by the sowbug's two small appendages called uropods that extend from its hind end, which pillbugs lack. Collectively, these critters are also called woodlice, roly polys or potato bugs.
Next time you encounter a pillbug, don't think bug--think kangaroos and lobsters.