Of all the things that turn up on a South Florida floor after a rainy week, pillbugs are probably the least threatening. Most people know them from childhood as roly-polies, the small grey creatures that curl into a tidy ball when you touch them, and finding a few in the garage or by the back door rarely causes much alarm.
Still, they raise a fair question. Why are they inside at all, and does it mean anything? The answer is more interesting than the bugs themselves, because pillbugs are less a pest than a moisture gauge, and the places they show up tell you something about what is happening along the outside of your house.
The quick answer
Pillbugs are harmless. They do not bite, sting, carry disease, or damage your home.
They are not insects. They are land-dwelling crustaceans, related to shrimp and crabs, and they need moisture to survive.
Finding them indoors usually means there is too much moisture right outside, in mulch, leaf litter, or wet soil along the foundation.
They tend to die quickly inside because the air is too dry, so the fix is outside, not in the house.
For a full profile of the species, including how to identify them up close, see our pillbug library page. This article covers the question most people are actually asking: why they are in the house, and what to do about it.
Pillbugs look like bugs, but they belong to a different group entirely. According to UF/IFAS, the common pillbug is Armadillidium vulgare, a terrestrial isopod — a crustacean, which makes it a closer relative of shrimp and crabs than of any insect in your yard.
That family connection explains almost everything about how they behave. Like their aquatic relatives, pillbugs breathe through gill-like structures that only work when they stay moist. Dry air pulls water out of their bodies quickly, so they spend their lives in damp, sheltered places and come out mostly at night or after rain, when the air is humid enough for them to move around.
Two closely related creatures get lumped together, and the difference is easy to spot. UF/IFAS notes that people regularly call one the other.
Pillbugs roll up.
Touch one and it curls into a near-perfect ball, which is where the roly-poly name comes from. Their bodies are rounded and they have no visible tail.
Sowbugs cannot roll up.
They look flatter, and you can usually see two small tail-like points at the back end that get in the way of rolling. They live in the same places and behave the same way, so for a homeowner the distinction matters less than what both of them are telling you.
Pillbugs do not seek out your house. They end up inside by accident, usually after heavy rain floods the damp spots where they live, or after a hot, dry stretch drives them looking for moisture. They crawl in through gaps under doors, around garage door seals, and along the base of walls, often in garages and on ground floors close to the outside.
Once indoors, most of them do not last long. The air inside an air-conditioned home is far too dry for them, so they tend to dry out and die within a day or two. That is why people often find them dead in corners or along baseboards rather than living and multiplying inside.
This is the useful part. Pillbugs thrive where there is constant moisture and plenty of decaying organic material, so a steady stream of them near your foundation points to conditions worth looking at.
The usual culprits are mulch piled thick against the house, irrigation that keeps the soil along the foundation wet, leaf litter collecting in corners, and downspouts that empty right next to the wall. Potted plants, stepping stones, and stored items sitting on damp ground also give them shelter. Our guide on landscaping mistakes covers several of these.
Those same conditions matter for more than pillbugs. Moisture and organic material against the foundation are exactly what termites look for too, which is why the advice in our termite prevention guide overlaps so closely with keeping pillbugs out. They also bring in the other damp-loving pests covered in our guide to earwigs, silverfish and the moisture pests nobody talks about.
Very little. Pillbugs feed mainly on decaying plant material such as dead leaves, rotting mulch, and other organic debris, which makes them useful decomposers in a garden. They break down dead matter and return nutrients to the soil. UF/IFAS describes pillbugs found indoors as causing no damage at all, and being an annoyance rather than a problem.
When their numbers get very high in a damp spot, they can occasionally nibble tender seedlings or soft fruit resting on wet ground, but that is the extent of it. They do not damage the structure of your home, chew through wood, or harm people or pets. In most yards, they belong with the creatures doing more good than harm.
Because the cause is moisture, the solution starts outside. UF/IFAS advises against overwatering and recommends clearing away the decaying plant material that shelters them. In practice that means pulling mulch back so it does not sit against the foundation and keeping it thinner near the house, adjusting sprinklers so they water the lawn and beds rather than the walls, and clearing leaf litter from corners and along the base of the house.
Lift potted plants onto stands or feet so the ground beneath them can dry out, and make sure gutters and downspouts carry water away from the foundation.
Then close the way in. UF/IFAS recommends sealing cracks at floor level and around door entries, so door sweeps and a good seal along the bottom of the garage door stop most of them at the threshold. For the ones already inside, sweeping or vacuuming is all you need. There is no reason to spray, since they will not survive long indoors anyway.
A few pillbugs after a storm is nothing to think twice about. A steady supply of them indoors, week after week, is worth a closer look, because it usually means moisture is building up somewhere it should not.
That can point to a leak, poor drainage, or an area along the foundation that stays wet, and those are conditions that bring in more serious pests over time. If you are finding them consistently in the same room, check that area for dampness first.
If pillbugs keep turning up inside, there is usually a moisture problem along the foundation worth fixing. An inspection can find the source and check for other pests drawn to the same conditions. Wise House Pest Control offers a free inspection across Palm Beach County, Martin County, and St. Lucie County.
1177 Hypoluxo Rd Suite C-31 Lantana, FL 33462 (561) 727-8239
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They usually wander in by accident after heavy rain floods their outdoor habitat, or during dry spells when they go looking for moisture. A steady supply indoors generally means there is too much moisture along the outside of the house, in mulch, leaf litter, or wet soil near the foundation.
No. Pillbugs do not bite, sting, carry disease, or damage your home. UF/IFAS describes the ones that get indoors as causing no damage and being an annoyance rather than a threat to people or pets.
No. Pillbugs are isopods, a kind of land-dwelling crustacean, which makes them closer relatives of shrimp and crabs than of insects. They breathe through gill-like structures and need moisture to survive.
Pillbugs can roll into a ball and have rounded bodies with no visible tail. Sowbugs are flatter and have two small tail-like points at the back that stop them rolling. Both live in damp places and behave the same way, and UF/IFAS notes the two names get mixed up constantly.
Rarely. They feed mainly on decaying plant material and help break it down. When their numbers are very high in a damp spot, they can occasionally nibble tender seedlings or soft fruit resting on wet ground.
Reduce the moisture that attracts them. Pull mulch back from the foundation, adjust sprinklers away from the walls, clear leaf litter, lift potted plants off the ground, and seal cracks at floor level and around doors. Sweep or vacuum up any that get inside, since they dry out and die indoors anyway.
