Cellar spiders are not dangerous to humans. There is no documented case of a cellar spider biting a person and causing a harmful reaction. Despite a persistent myth claiming they carry the world’s deadliest venom, laboratory analysis shows their venom is far weaker than that of truly dangerous spiders like black widows. These gangly, web-spinning roommates are essentially harmless.
The “Most Venomous Spider” Myth
You’ve probably heard some version of it: cellar spiders are the most venomous spiders in the world, but their fangs are too short to bite you. Both halves of that claim are wrong.
Cellar spiders do have venom glands and venom ducts, just like other spiders. But their venom is not especially potent. In a controlled test documented in a 2019 study, arachnologist Charles Kristensen injected mice with venom from cellar spiders and black widow spiders separately. The black widow venom had a far more powerful effect. Rick Vetter, an arachnologist at UC Riverside, has put it plainly: “I’m not aware of any publication showing that pholcid spiders cause a toxic effect in humans.” One researcher who allowed a cellar spider to bite him reported a small dark mark that faded within a couple of days.
As for the fangs, cellar spiders do have short ones, but they aren’t incapable of piercing skin. Their fangs work like a pair of tongs, with a secondary tooth that closes against the main fang. The real point is that even if one did bite you, it wouldn’t matter much. The myth likely persists because, as Vetter explains, “somebody said it once and there was never enough knowledge to refute it. So it just goes on and on. And people love scary stories.”
Which “Daddy Longlegs” Are We Talking About?
Part of the confusion comes from the name “daddy longlegs,” which people use for three completely different creatures. Only one of them is a true spider.
- Cellar spiders (family Pholcidae) are the actual spiders. They have two distinct body segments, eight eyes, and spinnerets that produce silk for their messy, irregular webs. These are the ones you find hanging upside-down in basement corners.
- Harvestmen (order Opiliones) look like a single round body on stilts. Their head and abdomen are fused together, they have only two eyes, and they produce no silk and carry no venom at all.
- Crane flies (family Tipulidae) are insects, not arachnids. They have six legs, wings, and resemble oversized mosquitoes. They don’t bite or sting.
If someone tells you “daddy longlegs” are dangerous, it’s worth figuring out which animal they’re even talking about. Two of the three don’t have venom at all.
Cellar Spiders Actually Hunt Dangerous Spiders
Far from being a threat, cellar spiders are surprisingly effective predators of insects and other spiders, including species that genuinely can harm you. In some regions, they prey on black widow spiders and other venomous species, which is why they’re considered welcome houseguests.
Their hunting strategy is clever. Cellar spider webs aren’t sticky. Instead, they rely on a dense, tangled matrix of silk threads that snag and confuse prey. When something gets caught, the cellar spider throws additional silk from a safe distance, using those long legs to wrap its target without ever putting its body in danger. They routinely take down prey much larger than themselves, including wolf spiders and crane flies.
Some species are even more cunning. They’ll sneak into another spider’s web, jiggle the threads to mimic a trapped insect, and then bite the host spider when it comes to investigate. This aggressive mimicry lets them turn other spiders’ traps against them.
Managing Cellar Spiders at Home
Since cellar spiders pose no risk and eat other pests, many people choose to leave them alone. But if the webs bother you or the population has gotten out of hand, you don’t need chemicals to deal with them.
A vacuum cleaner or broom is the most effective tool. It removes the spiders, their webs, and their egg sacs in one pass. Destroying egg sacs matters because each one can contain hundreds of young spiders. Regular cleaning in the areas they prefer, like basements, garages, closets, and attics, discourages them from settling in.
Reducing clutter in quiet, undisturbed corners makes those spaces less appealing. Moving firewood, stacked boxes, and debris away from your home’s foundation cuts down on spiders migrating indoors. Trimming shrubs, vines, and tree branches that touch the house removes the natural bridges spiders use to reach the structure. Tight-fitting window screens and door sweeps block entry points. Switching outdoor lights to yellow or sodium vapor bulbs attracts fewer night-flying insects, which in turn draws fewer spiders looking for a meal.