Woodlice in your house almost always point to a moisture problem. These small, armored creatures need damp conditions to survive, and when they show up indoors in significant numbers, they’re telling you something about the humidity levels in your home. The good news: they’re completely harmless to you and your property.
Why Woodlice Come Indoors
Woodlice breathe through gill-like structures, which means they dry out and die without moisture. Their optimal humidity range falls between about 52% and 75% relative humidity. In lab experiments, woodlice placed in completely dry conditions moved about frantically until they died, while those in moderate humidity settled comfortably. This biological need for dampness is the single biggest reason they end up in your home.
Most woodlice wander inside during cooler autumn and winter months, looking for shelter from the cold. A buildup of vegetation, leaf litter, or mulch against the outside of your house makes the journey easier by creating a damp bridge right to your walls. In these cases, you might find one or two and think nothing of it.
When you’re seeing large numbers indoors, though, the cause is usually condensation, a leak, or persistent dampness inside the house itself. Kitchens, bathrooms, basements, and poorly ventilated crawl spaces are the most common hotspots. The woodlice aren’t creating the moisture problem. They’re just the visible symptom of one that already exists.
What Woodlice Look Like
Woodlice are crustaceans, not insects. They’re more closely related to shrimp and crabs than to any bug in your house. Adults have an oval, arched body covered in overlapping armored plates, with seven pairs of legs and short antennae about a quarter of their body length. Most are between a third and three-quarters of an inch long, and they’re typically grey or brown.
You may hear them called by different names depending on where you live. In North America, the two most common types are pillbugs and sowbugs. Pillbugs are the ones that curl into a tight ball when disturbed. Sowbugs have a flatter body profile, can’t roll up, and have two small tail-like appendages at the rear. In the UK, the species most often found indoors is the common garden woodlouse. All of them share the same moisture dependency and the same harmless nature.
Are They Harmful?
Woodlice don’t sting, don’t bite, don’t transmit disease, and don’t damage your home’s structure or furnishings. They are purely a nuisance. Unlike termites or carpenter ants, they aren’t eating your wood or weakening your walls. They feed on decaying organic matter like dead leaves and rotting wood, not on anything you’d find inside a healthy home.
Outdoors, they can nibble young seedlings and ripening strawberries, so gardeners sometimes consider them a mild pest. But inside your house, they pose zero risk. The real concern when you see them in numbers isn’t the woodlice themselves. It’s the dampness they’re flagging, which can lead to mold growth, mildew, and actual structural issues if left unaddressed.
How to Get Rid of Them
You can vacuum up any woodlice you see. That handles the immediate annoyance. But if you stop there and don’t address the moisture, they’ll keep coming back.
The core fix is making your home drier and harder to enter:
- Find and fix leaks. Check pipes, gutters, and downspouts. Woodlice spotted in upper areas of your home can signal a problem in the guttering itself.
- Improve ventilation. Basements, crawl spaces, and bathrooms are priority areas. A dehumidifier can bring persistently damp spaces under control. Aim for basement or crawl space humidity below roughly 50%, which is below the comfort zone woodlice need to survive.
- Clear vegetation from your foundation. Pull mulch, leaf litter, compost, and firewood at least several inches away from exterior walls. These materials hold moisture and give woodlice a perfect staging ground.
- Seal entry points. Check for cracks and gaps in your foundation, around door frames, and where pipes enter the building. Even small gaps in older mortar or weatherstripping can let them through.
- Clean your gutters. Blocked gutters cause water to pool and overflow against walls, creating exactly the damp conditions woodlice love.
Using Diatomaceous Earth
If you want a chemical-free option beyond environmental fixes, food-grade diatomaceous earth works well against woodlice. It’s a fine powder made from fossilized algae that damages the waxy coating on their shells, causing them to lose moisture and die. You can dust it along baseboards, in cracks, behind appliances, and in other spots where woodlice tend to gather.
Diatomaceous earth is non-toxic to people and pets, but it does need to stay dry to work. In a damp basement, it’ll clump and lose effectiveness, which circles back to the main point: reducing moisture is the foundation of any lasting solution. Insecticide sprays and perimeter granules exist, but they’re rarely necessary for woodlice. Fix the dampness, seal the gaps, and the woodlice lose their reason to be there.
What a Persistent Problem Means
A handful of woodlice wandering in during autumn is normal and nothing to worry about. Sweep them up or carry them back outside. But if you’re finding them regularly, especially in rooms away from ground level, treat it as a diagnostic clue. Somewhere in your home, moisture is accumulating in a way it shouldn’t be. Common culprits include a slow pipe leak behind a wall, condensation from poor insulation, a bathroom fan that vents into the attic instead of outside, or rising damp in older buildings without a proper damp-proof course.
Addressing the underlying moisture issue solves the woodlice problem permanently and protects your home from more serious damage like mold, wood rot, and compromised insulation. The woodlice are just the messengers.