A woodlouse spider in your house is not dangerous and not a sign of an infestation. These distinctive, red-bodied spiders are solitary hunters that wander indoors looking for their favorite prey: pill bugs (also called roly-polies or woodlice). Finding one usually means you have moisture and pill bugs nearby, and the spider followed the food source inside.
How to Identify a Woodlouse Spider
Woodlouse spiders are easy to identify once you know what to look for. They have a dark red to tawny orange head and legs paired with a smooth, shiny abdomen that ranges from pale beige to yellow-brown, sometimes tipping into dark grey. Females measure 11 to 15 millimeters in body length (roughly the size of a fingernail), while males are slightly smaller at 9 to 10 millimeters.
The feature that catches most people’s attention is their fangs. Woodlouse spiders have oversized, forward-pointing mouthparts called chelicerae that look disproportionately large for their body. These thick, slanted fangs are purpose-built for cracking through the tough armor of pill bugs, piercing the soft underside to inject venom. They also have only six eyes, arranged in two clusters of three, which is fewer than the eight eyes most spiders carry.
Why They Come Inside
Woodlouse spiders don’t seek out human living spaces on purpose. They follow pill bugs, and pill bugs follow moisture. If your home has damp areas, particularly around basements, bathrooms, crawl spaces, or ground-level entry points, pill bugs may already be living there. The spider comes in after them. During winter especially, spiders of many species move indoors searching for prey, water, and mates. Woodlouse spiders can detect moisture through sensory organs on their legs, so a leaky pipe or chronically damp corner can draw them deeper into a home than they’d otherwise go.
They’re nocturnal and spend daylight hours hiding under rocks, logs, or debris outside. Indoors, you’ll typically find them in dark, undisturbed spots: behind furniture, in closets at ground level, or tucked into basement corners. They don’t build webs to catch prey. Instead, they actively hunt at night, which is why people usually spot them out in the open on a floor or wall after dark.
Are They Dangerous?
Woodlouse spiders can bite if you handle them or accidentally press against one, and those oversized fangs are strong enough to break skin. The bite is painful in the moment, similar to a bee sting, but the venom is not medically significant. Most people experience mild irritation comparable to a mosquito bite that resolves on its own. They pose the same low-level risk to cats and dogs.
These spiders are not aggressive. They bite only when provoked or trapped, and they have no interest in people. If you find one in your house, it’s focused on finding pill bugs, not on biting you.
Woodlouse Spider vs. Brown Recluse
The reddish color and prominent fangs lead many people to worry they’ve found a brown recluse. The two spiders are easy to tell apart with a close look. A woodlouse spider has a vivid red-orange head and legs with a contrasting pale abdomen, giving it a distinctly two-toned appearance. A brown recluse is uniformly tan to brown across its entire body, with fine hairs on its abdomen and a characteristic violin-shaped marking on its head.
Both species have six eyes instead of eight, but the arrangement differs. Woodlouse spider eyes sit in two groups of three (triads), while brown recluse eyes form three separated pairs (dyads). Brown recluses also have completely smooth, spineless legs with uniform coloring, whereas woodlouse spiders have noticeably darker, more robust legs. If the spider you’re looking at has a bright red head and oversized fangs jutting forward, it’s almost certainly a woodlouse spider.
How to Keep Them Out
Since woodlouse spiders follow pill bugs, and pill bugs follow moisture, the most effective strategy works from the inside out: remove the moisture, and both pests lose their reason to be there.
- Fix moisture problems. Repair leaky pipes, improve ventilation in basements and crawl spaces, and use a dehumidifier in chronically damp areas. Once pill bugs lose their moisture source, they leave or die off, and the spiders lose their food.
- Remove ground-level hiding spots. Clear leaf litter, mulch, firewood, and debris from directly against your foundation. These are daytime shelters for both pill bugs and woodlouse spiders.
- Seal entry points. Install tight-fitting door sweeps and window screens. Pay attention to gaps around foundation vents, garage doors, and crawl space entrances.
- Switch outdoor lighting. Yellow or sodium vapor bulbs at exterior doors attract fewer night-flying insects than standard white bulbs. Fewer insects near your doors means fewer spiders hunting near your doors.
- Clean regularly. Routine vacuuming and dusting in low-traffic areas like basements, closets, and behind furniture removes spiders, egg sacs, and the small arthropods they feed on. This is consistently cited by university entomology programs as the single most effective indoor spider control measure.
For homes with persistent spider activity, applying an insecticide as a barrier spray around the building perimeter can help. Focus on door thresholds, foundation edges, garage entrances, and vents. This creates a chemical boundary that reduces the number of spiders and prey insects making it inside.
What to Do With One You Find
If a woodlouse spider is sitting on your floor, the simplest approach is the glass-and-paper method: place a cup over it, slide a piece of paper underneath, and release it outside. They’re beneficial predators that help control pill bug populations around your home. Killing one won’t solve an underlying moisture or entry point problem, and there’s no practical reason to be concerned about a single spider. If you’re seeing them repeatedly, that’s your cue to check for damp conditions and pill bug activity near your foundation rather than to treat the spiders themselves.