The woodlouse spider (Dysdera crocata) is not dangerous to humans. It does have venom and fangs large enough to pierce skin, but its bite is virtually innocuous. The main symptom is minor pain that typically lasts less than an hour, and every documented case has resulted in complete recovery with no lasting damage.
Venomous, Not Poisonous
Technically, the woodlouse spider is venomous rather than poisonous. Venom is injected through a bite; poison is ingested or absorbed. But either way, the answer most people are looking for is the same: this spider poses no real medical threat. The pain from a bite appears to come mostly from the mechanical puncture of the skin by its oversized fangs rather than from the venom itself. In a review of verified bite cases published in the journal Toxicon, researchers found that the median pain duration was about 40 minutes. Roughly one third of bite victims described the pain as severe, but even in those cases, symptoms resolved completely.
Local swelling, redness, and moderate itchiness were the most common effects. Systemic symptoms, meaning effects beyond the bite site, were recorded in only a single case across the entire dataset. No bites produced tissue death, open wounds, or any secondary complications. Every lesion healed fully.
Why the Fangs Look So Alarming
Woodlouse spiders have disproportionately large, forward-pointing fangs that they readily bare when threatened. These fangs evolved for a very specific job: catching and eating woodlice (pill bugs or roly-polies). The spider uses one fang to spear the soft underside of a woodlouse while the other grips around the armored top surface like a pincer. That fang length and strength puts this species among the very few spiders in regions like Britain, which has around 680 spider species, that can actually break human skin.
The spider also has a strong proclivity to bite when handled or cornered, which makes encounters feel more dramatic than they are. Adults are notably aggressive, even toward each other. But “willing to bite” and “medically dangerous” are two very different things.
Often Mistaken for the Brown Recluse
Much of the fear around woodlouse spiders comes from misidentification. In the United States especially, they’re commonly mistaken for the brown recluse, a spider whose bite can cause serious necrotic wounds that take weeks or months to heal and leave large scars. Researchers have specifically flagged this confusion as a problem because it can lead to excessive or harmful treatment for a bite that needs none.
Telling them apart is straightforward once you know what to look for. The woodlouse spider has six eyes arranged in two clusters of three, a dark reddish-orange head and legs, and a pale grayish or pinkish abdomen with no markings. The brown recluse has six eyes arranged in three pairs, a uniform tan-to-brown color, and a distinctive violin-shaped marking on its back. If the spider you’re looking at has a shiny reddish front half and a plain cream-colored abdomen, it’s almost certainly a woodlouse spider.
Where You’ll Find Them
Woodlouse spiders are nocturnal hunters that live wherever woodlice do. That means damp, sheltered spots: under stones, logs, and garden debris, in cellars, basements, and occasionally kitchens. They’re common in gardens, churchyards, and waste ground across Europe and have been introduced widely in North America, Australia, and other regions. They don’t build webs to catch prey. Instead, they roam at night and return to a silk-lined retreat during the day.
Most bites happen when someone picks up a rock, moves firewood, or reaches into a dark space where a spider is resting. The spider doesn’t seek out humans, and bites are purely defensive.
What to Do if You’re Bitten
A woodlouse spider bite doesn’t require medical treatment in most cases. You can expect a sharp pinch followed by localized pain, some redness, and possibly mild swelling. These symptoms typically fade within an hour. For comfort, wash the bite area with mild soap and water, then apply a cool compress for 15 minutes or so to ease pain and swelling. A standard over-the-counter pain reliever can help if needed, and an antihistamine can address any itchiness.
There are no documented cases of anaphylaxis or serious allergic reactions from this species. There are also no confirmed cases of necrotic skin damage from woodlouse spider bites. If a bite produces symptoms that seem disproportionate, spreading redness, a wound that worsens over hours, or any systemic reaction, it’s worth considering whether the spider was correctly identified. Those symptoms are more consistent with other species entirely.