Pillbugs and sowbugs are occasional indoor pests, but despite their names, these tiny creatures are not bugs or insects at all, but rather small crustaceans more closely related to crayfish than to insects. Although pillbugs and sowbugs look quite similar with nearly identical behavior, they are distinctly different species. Pillbugs belong to the Armadillidium vulgare species, while sowbugs are officially labeled Oniscus asellus. Both belong to the Armadillidiidae family of terrestrial crustaceans, a group identified by the rounded shape of their exoskeletons.
Pillbugs and sowbugs look pretty much the same:
- 1/4 to 1/2 inch long
- 7 pairs of legs
- 2 pairs of antennae, though one pair cannot be easily seen
- Dark gray to white; or may be solid-colored or patterned
- Rounded bodies that are convex on top and concave on the bottom
Harmless Outdoor Creatures, But Indoor Pests
Both species fall into a group of species commonly called woodlice, so named for their preference for feeding on decaying wood material. They are usually outdoor creatures, where they serve a valuable function for breaking down dead wood material. A forest without species such as woodlice would become overwhelmed with fallen branches and trees. The action of breaking down dead wood also serves to return valuable nutrients to the soil.
Pillbugs and sowbugs can occasionally become an issue for homeowners when they find their way indoors to feed on decaying plant material, such as rotting wood or paper. If a wooden threshold or sill plate begins to rot, for example, you may well find these creatures feeding on the rotting wood. Or, if a pile of old newspapers is left laying on a damp floor, it won't be long before one or both of these species begins to feed on the decaying material.
Pillbugs and sowbugs are, however, utterly harmless, and getting rid of them is best handled by simply removing the decaying material and moisture. The repulsion people sometimes feel for these creatures is mostly because of their primitive, alien appearance, not because they pose any risk.
Biology and Behavior
PIllbugs and sowbugs are most often found outdoors beneath stones, rocks, boards, leaf litter, and other items lying on the ground where it is moist. They may migrate indoors into damp basements or crawl spaces, usually entering the home at ground level. They will survive indoors, however, only if moisture is present. They generally remain hidden unless their shelter is disturbed, though sometimes may roam out into the open at night.
Both species are scavengers, feeding mostly on decomposing organic matter, though they do sometimes feed at ground level on young plants or on vegetable fruits that are contacting the ground, such as cucumbers or melons.
Unlike most insects, which have a relatively short life cycle, these tiny crustaceans can live up to three years. The reproduction cycle is relatively simple: The females carry eggs in a pouch on the underside of the abdomen, which hatch within two to seven weeks. The young creatures are small versions of the adults, and they are carried in the mother's pouch for about two months before setting off on their own. It will take about a year for the juveniles to reach adult size and begin reproducing.
4 Ways to Get Rid of Pillbugs and Sowbugs in Your Home
Remove Decaying Material
Along with requiring moisture, pillbugs and sowbugs seek out dead, decaying wood and other plant-based material, such as paper or cardboard. Lift a pile of damp cardboard or a plank of plywood lying on a concrete floor, and there's a good chance that some pillbugs and sowbugs will scurry away. Removing this material will generally rid your home of these pests.
These creatures are also often found in structural framing with decay, such as the foundation-level sill plates for walls or the wooden thresholds for doors. You can get rid of sowbugs and pillbugs by removing and replacing any damaged wood.
Remove Moisture Sources
Sowbugs and pillbugs require moisture to survive, and if that moisture is removed, they typically die within about two days. Drying up moist areas is more effective than chemical sprays when comes to getting rid of these creatures.
Habitual problems with sowbugs and pillbugs in structural framing are often because the landscaping is allowing water runoff from the roof to saturate the walls, or because too much mulch around the foundation keeps conditions moist. Correcting water runoff problems and keeping the ground around exterior walls dry will do wonders for getting rid of pillbugs and sowbugs.
Cover Damp Areas With Diatomaceous Earth
In areas of a concrete slab or basement floor, sprinkling DE (diatomaceous earth) on areas that are habitually wet will absorb moisture and kill pillbugs and sowbugs. The DE also serves as a repellant, as the pests find it unpleasant to crawl across.
Spray With Garlic Solution
Spraying damp floor areas with a garlic/water solution often causes pillbugs and sowbugs to flee. A pepper solution can also offer the same benefit.
What Causes Pillbugs and Sowbugs?
PIllbugs and sowbugs seek habitats that offer both moisture and decaying plant material. In indoor environments, this means they can be present wherever wood, paper, houseplant debris, or other organic plant material is allowed to lie and absorb moisture. Unlike many scavenger insect pests, these are not creatures that seek decaying animal matter, but rather feed almost exclusively on plant material.
Without both moisture and decaying plant material simultaneously present, there's little likelihood that pillbugs and sowbugs will be a problem.
How to Prevent Pillbugs and Sowbugs
As with most pests, the best way to keep outdoor sowbugs and pillbugs from finding their way indoors is by sealing all cracks, crevices, and gaps in the foundation and around vents, cables, wires, doors, and windows (especially at thresholds). Particular emphasis should be paid to ground-level areas, as this is where the bugs most frequently enter, and where moisture is most likely to be present.
But these are very tiny creatures that can find their way indoors through the smallest of openings, so combined with sealing any visible gaps, take measures to eliminate moisture sources and organic material. Without moisture and food sources, neither of these species will have any interest in entering your home or remaining.
Keep the area around foundations clear of plant debris and mulch to eliminate the prime habitat for sowbugs and pillbugs and prevent them from migrating indoors. Keep a 1- to 2-foot buffer around the foundation between the walls and any landcscape plantings.
Indoors, keep cardboard, paper, wood, and similar materials off the floor, and get rid of any such material that shows signs of decay.
As a last resort, a perimeter application of an insecticide labeled for sowbugs/pillbugs can provide some preventive control in keeping these, and other occasional invaders, out of your home. Such an insecticide can be applied along the bottom doors, vent and utility opening, and underneath the bottom edge of siding. You can also spray where the ground meets the foundation.
Chemical pesticides should be considered a last resort when it comes to controlling pillbugs and sowbugs, since many are known carcinogens. It's usually best to avoid toxic chemicals in favor of simply eliminating feeding/breeding areas for the creatures. Be aware that ordinary insecticides may not work, since pillbugs and sowbugs are crustaceans, not insects.
Chemicals that do work to kill and repel pillbugs and sowbugs include:
Pillbugs vs. Sowbugs
These species are quite similar, but pillbugs (Armadillidium vulgare) are so named for their ability to curl up in tight pill-like balls. Pillbugs are also known as potato bugs or roly-polies.
Sowbugs (Oniscus asellus) are slightly larger, flatter creatures, and they are unable to draw themselves up into a ball. When disturbed, they will quickly scurry away seeking cover. Sowbugs also have a tail-like structure that is not present in pillbugs.
Curl up into pill-like balls
Cannot curl up
Larger and flatter
Do pillbugs and sowbugs bite?
Neither pillbugs nor sowbugs have mouthparts capable of biting flesh. They are among the most innocuous and harmless of all creatures normally considered pests.
Are pillbugs and sowbugs useful?
Outdoors, both these creatures serve a valuable ecological function in breaking down dead plant material and returning the organic nutrients to the soil. When you apply a heavy mulch to your garden, you should expect and appreciate the arrival of sowbugs and pillbugs to break down the organic material into nutrients that are useful to plants. And wildlife lovers will enjoy the fact that songbirds, toads, and other small predators feed on pillbugs and sowbugs.
Indoors, the presence of these creatures indoors is useful as an alert that there is decaying material present. This condition should be addressed so as to ensure the decay doesn't spread.
Do pillbugs and sowbugs carry or spread disease?
Despite some proclamations by extermination experts seeking to sell their services, neither sowbugs nor pillbugs are known to carry or spread diseases. While it's true that the decaying plant material upon which these species feed may foster bacteria that could be harmful, sowbugs and pillbugs do not spread the pathogens around; in fact, they may reduce possible transmission by consuming the decaying matter.
Do people keep pillbugs as pets?
Although it sounds strange, keeping pillbugs in a sealed terrarium or glass jar is sometimes popular with children as an experiment in observing natural ecology. These are utterly harmless creatures, and it can be instructive to watch the manner in which nature breaks down dead material. All that's required is to provide the bugs with a regular diet of moist paper, wood chips, or compost layered over some ordinary soil. Make sure the container is well-ventilated, as these creatures need air to thrive.
"Pillbugs and Sowbugs." NC State Extension Publications.
“Sowbugs and Pillbugs: Occasional but Destructive Greenhouse Pests.” Penn State Extension.