The spider you’re seeing in your basement is most likely a long-bodied cellar spider (Pholcus phalangioides), a pale, delicate spider with extremely long legs that hangs upside down in messy, irregular webs. It’s harmless to you and actually one of the more effective pest hunters you could have in your home. A second common candidate is the funnel weaver group, which includes the barn funnel weaver and giant house spider, both of which build sheet-like webs in dark, damp corners.
How to Identify a Cellar Spider
Cellar spiders have a small, elongated body (about 7/16 of an inch long) but a leg span that makes them look far larger. Their legs are thin and almost translucent, and their bodies range from pale tan to light gray. They hang belly-up in loose, tangled webs that look messy and shapeless compared to the neat, geometric orb webs you see outside. These webs are often built in corners, along ceiling joists, around pipes, and near windows where small insects drift in.
If you walk up to one quickly, you’ll notice something distinctive: the spider starts vibrating its body in rapid circles while its legs stay fixed to the web. This “whirling” makes the spider blur into invisibility against its web, which is a defense mechanism rather than aggression. The duration depends on what triggered it. A light touch to the web produces a brief spin. The presence of a jumping spider, one of their natural predators, can keep them whirling for hours or even days, since the rapid movement disrupts the jumping spider’s normally sharp vision.
Funnel Weavers: The Other Basement Spider
If the spider you’re seeing is brown, bulkier, and built a flat sheet web with a funnel-shaped retreat in one corner, it’s likely a funnel weaver in the Tegenaria family. Three species commonly show up in homes: the barn funnel weaver, the giant house spider, and the hobo spider. All of them prefer dark, moist areas like basements, crawl spaces, and woodpiles. They’re fast runners on flat surfaces, which can be startling, but they’re not aggressive toward people and rarely bite.
Why Cellar Spiders Are Effective Hunters
Cellar spiders are surprisingly aggressive predators for their fragile appearance. They eat flies, mosquitoes, gnats, and other small insects that get caught in their webs. But what sets them apart is that they actively hunt other spiders. Rather than waiting passively for prey, a cellar spider will leave its own web and approach another spider’s web. It creates vibrations that mimic a trapped insect, tricking the resident spider into investigating. When the prey spider gets close enough to touch one of the cellar spider’s legs, the cellar spider uses its long reach to wrap the victim in silk from a safe distance, avoiding a retaliatory bite. Then it delivers a venomous bite to finish the job.
This hunting strategy means cellar spiders tend to reduce the overall spider population in your basement over time. They’ll also eat spider eggs, further limiting other species’ numbers. If prey happens to stumble near the edge of their web, cellar spiders can cling to the web with just two legs while leaning out and shooting silk at the target with the rest of their body.
Can They Bite You?
There’s a persistent myth that cellar spiders have the most potent venom of any spider but can’t bite through human skin. Both parts of that claim are wrong. Adult males can pierce uncalloused human skin, and their venom is far weaker than a black widow’s, not stronger. Research published in Frontiers in Ecology and Evolution tested the venom of a closely related cellar spider species directly. When researchers injected equal volumes of cellar spider venom and black widow venom into mice, the black widow venom was significantly more potent. Extracting just one microliter of cellar spider venom required milking 50 to 100 adult males, and even that amount produced no lethal effects.
The only well-documented human bites from cellar spiders came from a Mythbusters episode, where an agitated male spider bit a person. The result was a brief, mild sting with no lasting effects. In practical terms, cellar spiders pose zero medical risk. Their venom is effective against insects and other spiders but inconsequential to mammals.
Lifespan and Reproduction
Cellar spiders develop from egg to adult in about one year, and adults can live an additional two years after reaching maturity. That means a single spider can occupy your basement for up to three years. Female long-bodied cellar spiders produce about three egg sacs over their lifetime, each containing 13 to 60 eggs. You’ll sometimes see a female holding a loose bundle of eggs in her jaws rather than attaching them to the web. This is normal behavior, and she’ll carry the eggs until they hatch.
Because each female can produce well over 100 offspring in a lifetime, populations can build up noticeably in an undisturbed basement. The webs accumulate too, since cellar spiders don’t take down old webs. This is what creates the dusty, layered cobweb look that most people find unappealing, even if the spiders themselves are harmless.
How to Reduce Basement Spiders
If you’re comfortable coexisting with a few cellar spiders, they’ll keep your insect population in check. But if the webs are getting out of hand or the population has grown too large, a few environmental changes make a real difference.
Start with moisture. Spiders and the insects they eat both thrive in damp environments. Check for leaks around pipes, walls, and windows, and fix them promptly. Running a dehumidifier makes your basement less hospitable to both spiders and their prey. Proper ventilation helps too, whether that’s a fan, open vents, or improved airflow.
Decluttering removes hiding spots. Spiders set up webs in undisturbed areas, so stacks of cardboard boxes, old furniture, and piles of stored items are ideal habitat. Switching to sealed plastic containers and keeping items off the floor eliminates nesting opportunities and makes it easier to spot and remove webs.
Seal entry points next. Inspect your foundation walls, window frames, and utility entry points for cracks and gaps. Caulk or weatherstrip anything that could let insects in, because reducing the food supply is the most reliable way to reduce the spider population. Install door sweeps, repair damaged window screens, and check where pipes and wires enter the house.
Improving lighting also helps. Spiders prefer dark, shadowed corners where their webs go undisturbed. Brighter overhead lights or motion-activated lighting in corners discourages web-building. Routinely sweeping or vacuuming webs from corners, ceilings, and around storage areas disrupts established territories and discourages spiders from rebuilding in the same spots.
Outside the house, keep shrubs and tree branches trimmed away from exterior walls. Woodpiles, dense vegetation, and debris near the foundation provide shelter for insects, which in turn attract spiders indoors. Moving these features away from the house reduces the number of spiders that find their way inside in the first place.