What Is a Roly Poly? (Bug, Insect, or Crustacean?)

You flipped a rock as a kid, and there it was: a tiny gray armored critter that curled into a perfect little ball the second you touched it. You probably called it a roly poly. Your cousin called it a pill bug. Your grandpa called it a potato bug. Someone in England called it a woodlouse.

So what is it, really?

Short answer: a roly poly is an isopod, and isopods aren't bugs at all. They're crustaceans.

Is a Roly Poly an Insect?

Nope. Insects have six legs and three body sections. A roly poly has 14 legs (seven pairs) and belongs to a completely different group of animals: the crustaceans. That makes it a closer relative of shrimp, crabs and lobsters than of beetles or ants.

In fact, roly polies are one of the few crustaceans that live their whole lives on land. They still carry a little of the ocean with them, though: they breathe through specialized structures on their underside that need moisture to work. That's why you always find them in damp places, under rocks, logs and leaf litter, and why they dry out fast in the sun.

What's a Roly Poly's Real Name?

Scientists call them isopods (order Isopoda). The land-living kind are terrestrial isopods. The classic roly poly most people grew up with is usually Armadillidium vulgare, the common pill bug.

Fun fact: Armadillidium comes from the same root as "armadillo," and for good reason. Like an armadillo, a pill bug rolls into an armored ball to protect itself. Biologists call that move conglobation. We call it adorable.

Roly Poly vs. Pill Bug vs. Sow Bug vs. Woodlouse

• Roly poly / pill bug: isopods that can roll into a tight ball, like our Armadillidium (Zebras, Magic Potions, Clowns). Many Cubaris can roll up too.
• Sow bug: isopods that generally can't roll up completely. They run instead. Our Porcellio (Dairy Cows, Lavas) fall in this group.
• Woodlouse / woodlice: the British term for terrestrial isopods in general.
• Potato bug: a regional nickname. (Just don't confuse it with the Jerusalem cricket, which also gets called a potato bug and is a whole different, much scarier-looking animal.)

The Giant Isopod "Sea Roly Poly"

If you've seen viral videos of a huge roly poly the size of a cat, you've met the giant isopod (Bathynomus). It's a real isopod, a distant cousin of the little guys in your garden, but it lives on the deep ocean floor and can grow over a foot long. And no, it isn't a pet. (Please don't try.)

If you want the biggest isopods you can actually keep at home, check out our big isopods.

Do Roly Polies Bite?

No. Isopods have tiny mouthparts designed for munching decaying leaves and wood, not people. They're completely harmless to handle, which is part of why kids love them.

Roly Polies in the House?

If you find a few indoors, they're usually just looking for moisture. They don't damage your home, and most won't survive long inside because it's too dry for them. Gently carry them back outside to a damp, shady spot.

Why Do People Keep Isopods as Pets?

Because they're quiet, fascinating, easy to care for, and they come in colors your backyard roly polies never dreamed of: orange, blue, pink, black-and-white "dairy cows," even ones with faces like rubber ducks. Isopods also work as a clean-up crew in bioactive reptile and amphibian enclosures, eating waste and decaying matter. (New to that idea? Read What Does It Mean to Go Bioactive?)

Ready to keep some? Start with Just Getting Started? and our Isopod Recommendations, then browse our fast-breeding isopods or all isopods.

Roly Poly FAQ

Is a roly poly a bug? Not technically. It's a crustacean, related to shrimp and crabs.

How many legs does a roly poly have? Fourteen, in seven pairs.

Why do roly polies roll up? To protect their soft underside from predators and to hold in moisture.

Can you keep roly polies as pets? Absolutely. They need moisture, decaying leaves and wood, a calcium source, and a little patience.

Thanks for rolling with us!