Are Sow Bugs, Pill Bugs and Roly-Polies the Same Thing?

If you have a garden, a compost, or a wood pile, it's almost certain you’ve seen isopods crawling and rolling about. Isopods are arthropods, but not insects, characterized by their flattened, segmented bodies and seven pairs of legs. To be even more specific, isopods are technical crustaceans that are more closely related to crabs and lobsters than to other terrestrial arthropods, such as centipedes and millipedes. 

The most well-known terrestrial isopods are rollie pollies (Roly-poly? Roly-polie? There really isn’t a consistent way of spelling it, so I’m deferring to how the NPMA chooses to spell rollie pollies), sow bugs, and pill bugs, which aren't actually bugs at all. But wait – aren't these all the same bug, just going by different names? Not exactly, but it’s an easy mistake to make. After all, sow bugs and pill bugs share a lot of similarities in their diet, habitat, and life cycle (we’ll talk about rollie pollies later). But at the end of the day, sow bugs and pill bugs are two completely different types of isopods with distinct characteristics.

Shared Characteristics

Both sow bugs and pill bugs are nocturnal, preferring to stay hidden during the day in areas with lots of moisture and decaying plant material. That's why leaf piles, lawn clippings, stumps, and soil are just some of the places these isopods are usually found. While both sow bugs and pill bugs are harmless, they can become pests when they feed on seeds, saplings, and roots of plants in your garden. Additionally, these critters can sometimes invade homes if potted plants are brought inside. Again, these pests won't cause structural damage to the home, but they may crawl throughout the house in search of moisture sources.

Sow Bugs (family: Porcellionidae)

Sow bugs are generally flatter and larger than pill bugs, usually averaging ½ to ¾ inches in size. They're often described as having a light or dusty grey color, and two tail-like appendages can be found at the back of their abdomen. Sow bugs can occupy the same habitats as pill bugs, though they are more likely to infest basements and homes, given their flat anatomy and ability to enter through small cracks and crevices. Pill bugs prefer staying in areas rich in organic matter, typically outside.

Pill Bugs (family: Armadillididae)

Pill bugs are chunkier and smaller than sow bugs, usually averaging about ¼ - ½ inches in size. Pill bugs are darker than sow bugs, generally appearing in deep grey or black. Unlike sow bugs, these isopods do not have any tail-like appendages. The most significant difference between sow bugs and pill bugs is whether they can curl up. Pill bugs can roll into a tight ball when threatened or to retain water, while sow bugs can't.

What’s In A Name?

You’ll notice that I haven’t mentioned anything about rollie pollies yet. That’s because rollie pollies are another way of saying pill bugs. The only difference between rollie pollies and pill bugs is what you call them, because they are the same animal!

This is a common trend in entomology: multiple common names for the same organism, often derived from regional dialects and geographic colloquialisms. If you have ever lived in the southern United States, you may have heard people complain about "Palmetto bugs" or "Water bugs," when, in fact, they're talking about American or Oriental cockroaches. The same thing happens when we talk about lightning bugs or fireflies; it’s the same insect, just called by a different name.

Ultimately, it isn't the end of the world to have multiple common names for the same arthropods. But it makes pest management, vector surveillance, and biodiversity mapping difficult when a single species is represented by various names, or when multiple organisms are described by the same name. That's why entomologists tend to refer to insects and arthropods by the scientific names of their order, genus, or species. When each arthropod has its own unique genus and species, we can be certain we're talking about the same organism without worry about regional differences in speaking.

So whether you’re dealing with a Porcellionidae or an Armadillididae, now you know that sow bugs and pill bugs are NOT the same thing!

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