A roly-poly is a small gray creature that looks like a tiny armored tank and rolls into a perfect ball when frightened. You've probably found them under rocks, logs, or flowerpots in your yard. They have segmented shells and lots of little legs, and when you touch one, it curls up tight to protect itself, which is where the name comes from.

Despite looking like insects, roly-polies are actually crustaceans, relatives of crabs and lobsters. Scientists call them pill bugs or woodlice. They breathe through gills and need moisture to survive, which is why they hide in damp, dark places. They eat decaying plants and help break down dead leaves into soil, making them important members of the backyard cleanup crew.

The word roly-poly can also describe anything pleasantly round and chubby. A plump puppy might be called roly-poly, and there's even a British dessert called roly-poly pudding: a rolled-up, jam-filled cake that looks roly-poly too.