Not medically significant, but it is one of the few spiders that will bite if handled, and its fangs are big enough to break skin easily. The bite stings for an hour or two and does no lasting harm. It is worth knowing because it is regularly mistaken for a brown recluse.
We identify, we don't diagnose. If you've been bitten or stung and symptoms develop, or you're worried, seek medical attention.
Size9–15 mm body
MarkingsGlossy dark red or orange front half with a plain cream to grey abdomen · Very large forward-projecting fangs, obvious even without magnification
WhereDamp ground-level cover: under stones, logs, bark, flowerpots and in leaf litter. Indoors it turns up in basements and ground-floor rooms.
What it is not
A woodlouse spider is most often confused with a species that is medically significant. If you are trying to rule those out, check these:
Glossy dark red or orange front half with a plain cream to grey abdomen
Very large forward-projecting fangs, obvious even without magnification
Six eyes — like a recluse, which is why the eye test alone is not enough here
No web; found under stones, logs and damp debris
Legs uniformly reddish, quite short and stout
Where you’ll find it
Introduced from Europe and now established across much of the United States, including large parts of the west and northeast where brown recluses do not occur at all.
Damp ground-level cover: under stones, logs, bark, flowerpots and in leaf litter. Indoors it turns up in basements and ground-floor rooms.
How it behaves
It hunts woodlice, almost exclusively — those oversized fangs exist to puncture an armoured isopod, which most spiders cannot manage. It is nocturnal, builds no capture web, and spends the day in a silk retreat under cover. It is not aggressive but it is willing to defend itself, which is unusual among the spiders people pick up.
What a bite looks like
A pair of small puncture marks with local redness, sometimes with mild swelling. It settles within a day and does not ulcerate.
A sharp sting at the time, comparable to a bee, fading to soreness over an hour or two.
We identify, we don't diagnose. The bite is not medically significant, but see a doctor if the site becomes infected or the reaction is unusual.
A skin mark cannot confirm which animal caused it. Read the bug bite and sting guide for the limits and the symptoms that should end an online search.
You’ve found one indoors
Do not pick it up — this is one of the few spiders where that advice is practical rather than theoretical. Glass and card works fine. Reducing damp harbourage outside the door reduces both this spider and the woodlice it is following.
Common questions
Is a woodlouse spider a brown recluse?
No, though it is one of the commonest false alarms. Both have six eyes, which is the character people are told to check. The separator is colour and build: a woodlouse spider has a glossy dark red front half, a pale plain abdomen and very obvious fangs, while a recluse is uniformly tan with a violin mark and much longer, finer legs.
Does a woodlouse spider bite hurt?
Yes, briefly. Its fangs are large enough to break skin cleanly and the sting is comparable to a bee. It fades within a couple of hours and does no lasting damage.
Why is it in my house?
It is following woodlice. Where you have damp at ground level you get woodlice, and where you get woodlice you eventually get the spider that specialises in eating them.
Tone Killick · CC-BY