Cellar spiders are not dangerous to humans. They do have venom, which technically makes them venomous rather than poisonous, but that venom is remarkably mild and has never been documented causing a harmful reaction in a person. The widespread claim that cellar spiders carry the world’s deadliest venom but can’t deliver it is a myth with no scientific support.
Venomous vs. Poisonous
The distinction matters here. Something poisonous harms you when you touch, inhale, or swallow it. Something venomous injects a toxin through a bite or sting. Since cellar spiders deliver their venom through fangs, they’re venomous, not poisonous. In practical terms, though, it barely matters: their venom is so weak to humans that it falls into neither category in any meaningful way.
The “Deadliest Venom” Myth
You’ve probably heard some version of this: cellar spiders have the most potent venom of any spider, but their fangs are too small to pierce human skin. Both parts of this claim are wrong.
Cellar spiders can bite humans. Their fangs are small but functional. Rick Vetter, an arachnologist at the University of California, Riverside, has noted that one researcher who was bitten had a small black mark for a day or two and found the experience unremarkable. “Definitely not the most toxic spider in the world,” Vetter said.
The venom itself has been directly compared to that of genuinely dangerous spiders. On a 2004 episode of MythBusters, later documented in a 2019 study, arachnologist Charles Kristensen injected mice with venom from cellar spiders and black widows separately. Black widow venom was far more potent. Lab analysis of cellar spider venom shows it contains mostly small peptides under 30 kilodaltons that act as insect-specific neurotoxins. It lacks the tissue-spreading enzymes found in medically significant spider venoms. In short, the venom evolved to subdue tiny invertebrates, not large mammals.
The myth likely originated from an observable fact: cellar spiders routinely kill and eat black widows and other dangerous spiders. People assumed this meant cellar spiders must have even stronger venom. The real explanation is simpler. Cellar spiders hunt by casting long strands of silk onto their prey from a safe distance, binding the target before it can fight back. It’s a strategy, not superior chemistry.
What a Bite Feels Like
There is no documented case of a cellar spider bite causing a medically significant reaction in a human. UC Riverside’s spider research program states plainly that no reference exists to any cellar spider biting a person and causing a detrimental effect. The one informal account from a researcher describes mild, brief irritation comparable to a minor pinprick. Most people who live alongside cellar spiders for years never get bitten at all, because these spiders are not aggressive and their natural response to disturbance is to vibrate rapidly in their web rather than bite.
Cellar Spiders vs. Harvestmen
Part of the confusion around this topic comes from the name “daddy longlegs,” which gets applied to at least three completely different creatures: cellar spiders, harvestmen, and crane flies. Cellar spiders are the only true spiders in the group, and the only ones with venom at all.
Harvestmen (the round-bodied, outdoor creatures many people call daddy longlegs) have no fangs, no venom, and no silk glands. Their bodies appear to be a single oval segment, while cellar spiders have a clearly visible two-part body with a narrow waist between the head and abdomen. Harvestmen also have just two eyes compared to a spider’s typical six or eight. If you’re looking at a leggy creature hanging in a messy, irregular web in the corner of your basement, that’s a cellar spider. If it’s walking across the ground with no web in sight and its body looks like a single pill-shaped lump, that’s a harvestman.
Why They Live in Your Home
Cellar spiders gravitate toward dark, humid, undisturbed spaces. Basements, garages, crawl spaces, and the upper corners of closets are prime real estate. They build loose, irregular webs that accumulate over time into the wispy cobwebs most people associate with neglected rooms. Unlike orb-weaving spiders that rebuild neatly each day, cellar spiders simply add to existing web structures, which is why their webs look messy.
Their presence is generally beneficial. Cellar spiders eat mosquitoes, gnats, flies, and other small insects caught in their webs. In regions where black widows or other medically significant spiders live near homes, cellar spiders actively prey on them. The Missouri Department of Conservation notes that this predatory behavior makes cellar spiders “somewhat welcome” in areas where dangerous spiders are common. A cellar spider in your basement is essentially free, silent pest control that poses zero risk to you, your kids, or your pets.
Should You Remove Them?
If the cobwebs bother you, sweeping them away is the easiest approach and the spiders will typically relocate to a less disturbed spot. Sealing cracks around windows and doors reduces the insects that attract cellar spiders in the first place, which naturally lowers their numbers. Reducing humidity with a dehumidifier also makes a space less appealing to them. But from a safety standpoint, there’s no reason to worry about them. They’re harmless, and in homes where more dangerous spiders could wander in, they’re arguably working in your favor.