To get rid of woodlice (pillbugs and sowbugs) permanently: eliminate indoor dampness (woodlice breathe through gills and die of desiccation when relative humidity drops below 50%). Run a dehumidifier in damp basements and fix leaking pipes. Outdoors, clear wood mulch and wet leaves 3 feet away from foundation walls, and seal ground-level gaps with silicone caulk and heavy door sweeps. Chemical sprays are unnecessary.
Finding small, gray, multi-legged armored bugs crawling across your basement floor, curling into tight balls under the washing machine, or congregating near bathroom baseboards is a frequent occurrence in damp homes.
Commonly known as woodlice, pillbugs, sowbugs, or “roly-polies,” these creatures are not insects, they are terrestrial crustaceans (suborder Oniscidea), closely related to crabs and shrimp. Because they breathe through delicate modified gills (pleopodal lungs), they are completely dependent on ambient moisture to survive. A persistent presence of woodlice indoors is a biological alarm signaling hidden water leaks, saturated foundations, or structural decay.
🎯 Repellent Efficacy Ratings
Woodlice do not bite humans, transmit diseases, infest pantry food, or damage dry structural timber. They only consume already decaying organic matter and fungal mold. If you see them surviving indoors, treat the underlying moisture problem immediately, the damp conditions that keep woodlice alive also foster dangerous toxic mold and wood-destroying fungi.
Pillbug vs. Sowbug Diagnostic Matrix
Smooth arched slate-gray shell, 14 legs. Capable of complete conglobation (rolling into a perfect sphere) when disturbed.
Flatter body with two prominent tail-like appendages (uropods) projecting from rear. Escapes by running rather than curling up.
Silvery, teardrop-shaped true insect with 6 legs. Feeds on pantry starches, wallpaper paste, and book bindings.
Woodlice breathe via gills. In dry air (<50% humidity), they quickly desiccate and die within 24 to 48 hours.
Woodlice Control Methods Ranked by Efficacy
Step-by-Step Integrated Woodlice Exclusion Blueprint
Step 1, Indoor Moisture Control & Dehumidification
Exploit crustacean gill physiology to desiccate invaders.
- Place a compressor dehumidifier in basements, crawlspaces, or laundry rooms, setting the target relative humidity to below 50%.
- Inspect under bathroom sinks and around washing machine drain hoses for slow plumbing drips; repair immediately.
- Improve basement airflow using box fans and ensure clothes dryers vent completely outdoors without leaking moist exhaust.
- In air with less than 50% relative humidity, woodlice lose water rapidly through their gills and die of desiccation within 24 to 48 hours.
Step 2, Establish a 3-Foot Dry Foundation Border
Eliminate the damp outdoor breeding zone directly touching your home.
- Rake back bark mulch, rotting leaves, and pine needles at least 3 feet away from foundation walls.
- Replace organic mulch adjacent to the foundation with a 3-foot border of crushed stone or coarse pea gravel. Gravel drains instantly, creating a hot, dry desiccation barrier that woodlice refuse to cross.
- Move firewood stacks, compost piles, and decaying timber at least 20 feet away from the house.
- Extend gutter downspouts 6 feet away from the foundation to prevent soil saturation.
Step 3, Structural Exclusion & Sealing
Block ground-level foundation entry points.
- Install heavy rubber door sweeps on basement walkout doors, garage entryways, and exterior doors to eliminate daylight gaps.
- Caulk around foundation expansion joints, basement window frames, and exterior utility pipe penetrations with exterior silicone sealant.
- Insert stainless steel wire mesh into brick weep holes to allow wall drainage while physically barring woodlice.
Step 4, Desiccant Dusting in Voids
Protect dark voids with safe physical desiccants.
- Apply a light, microscopic dusting of food-grade diatomaceous earth or amorphous silica gel into the expansion gaps behind baseboards and under basement stairwells using a bulb duster.
- The microscopic silica particles absorb moisture and abrade the outer lipid coating of wandering isopods, accelerating dehydration.
Run dehumidifiers in basements to naturally desiccate woodlice gills in 24 hours.
Clear mulch 3 feet back from foundation and replace with fast-draining gravel.
Install heavy door sweeps and seal foundation gaps with silicone caulk.
Puff a microscopic dust film into baseboard gaps for long-lasting desiccation.
Myths vs. Facts About Woodlice
Woodlice cannot chew sound, dry structural wood. They are detritivores that only consume wood that has already been rotted and softened by severe water damage and fungal decay.
Woodlice are closely related to crabs and lobsters. They have 14 legs and pleopodal lungs that must stay damp to absorb oxygen; in dry air, they die of suffocation/desiccation.
Spraying insecticides is useless if high humidity remains. Simply running a dehumidifier drops moisture levels, causing woodlice to die naturally within 24 to 48 hours.
Pillbugs (*Armadillidium*) perform conglobation (curling into a tight protective armored sphere). Sowbugs (*Porcellio*) have two rear tail appendages (uropods) and must run away.
Frequently Asked Questions
Why do I suddenly find dead, curled-up woodlice in my hallway?
Woodlice wander indoors from outdoor gardens during heavy summer rains seeking shelter. Once inside your climate-controlled home, the low humidity quickly desiccates their gills, causing them to curl up and die of dehydration within hours.
Do woodlice carry diseases or bite pets?
No. Woodlice have chewing mouthparts designed exclusively for soft decaying plant matter. They do not bite humans or animals, produce venom, or transmit pathogenic bacteria.
Can woodlice damage houseplants?
In rare cases where potted plant soil is constantly saturated with water, woodlice will shelter in the pot and occasionally feed on tender emerging seedling roots. Allowing the soil to dry out or drenching with BTI resolves the issue.
What naturally eats woodlice in gardens?
Woodlice are an important food source for garden predators, including toads, frogs, ground beetles (Carabidae), centipedes, shrews, and the specialized woodlouse spider (Dysdera crocata), which has large fangs designed to pierce their armored shells.
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- 1. University of California Statewide IPM Program (UC IPM): Pillbugs and Sowbugs: Biology, Ecology, and Structural Moisture Management. Publication 7472.
- 2. Penn State Department of Entomology: Sowbugs and Pillbugs: Terrestrial Isopods as Bioindicators of Structural Moisture.
- 3. Journal of Crustacean Biology: Pleopodal Lung Morphology, Cuticular Respiration, and Desiccation Resistance in Oniscidea.
- 4. Ohio State University Extension: Sowbugs and Pillbugs Around the Home: Cultural Exclusion and Habitat Modification. HYG-2072.
- 5. Building Science Corporation: Basement Moisture Control, Relative Humidity Thresholds, and Pest Prevention in Below-Grade Enclosures.
HowToRepel.com is an independent educational resource, not a licensed pest control operator. While we consult peer-reviewed entomological studies, EPA documentation, and university extension research, always follow manufacturer EPA label instructions on commercial products or consult a licensed pest control operator for severe structural infestations. Read our full Safety & Content Disclaimer →
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