Cellar Spider — Pholcus phalangioides

The spider in the corner, and the story attached to it

There is a small-bodied spider on absurdly long thin legs hanging upside down in the corner of your basement, your garage, your laundry room or the underside of your deck. It has been there a while. The web around it has gone gray with dust.

Two things are worth knowing, and the second one is the reason this page runs long.

The animal is harmless, permanently and completely. And the single most widely repeated fact about it — that it carries the most powerful venom of any spider on earth and is saved from being lethal only by fangs too short to reach human skin — is not true, has never been true, and was never based on anything.

Sorting that out properly is what this page is for. It is the most successful piece of misinformation in the whole of arachnology, it is repeated by people who are otherwise careful, and untangling it also untangles the fact that “daddy longlegs” is used in this country for three animals that are not even distantly related.

Three unrelated animals, one nickname

Before anything else, because almost every argument about this subject is two people describing different creatures.

The cellar spider — Pholcus phalangioides, the animal this page is about. A genuine spider: two body sections, eight legs, silk, venom glands, the lot. Lives indoors, hangs inverted under a loose web, and is the only one of the three that is a spider at all. The Burke Museum’s summary of the confusion is that there is one daddy-longlegs that is a spider and a couple of thousand species that are not.

Harvestmen — the order Opiliones. These are the ones most Americans picture: a single pea-shaped body on eight extremely long legs, walking around under logs, on fence posts and across garden paths in daylight. The Burke’s formulation is the clearest one available: harvestmen are arachnids, but they are not spiders, in the same way that butterflies are insects but are not beetles. They build no web, they produce no silk, and — this is the part that matters below — they have no venom of any kind. None at all.

Crane flies — family Tipulidae. Insects. Six legs, two wings, and in British and some Canadian usage the name daddy longlegs refers to these and to nothing else. In this county the relevant one is the European crane fly, and WSU Hortsense records the adults emerging from lawns and pastures from late August through September, mosquito-like with long legs, about an inch long. The grub-stage larvae in the sod are called leatherjackets and they are a turf problem; the adult that blunders around a porch light in September is harmless and short-lived.

So when somebody says a daddy longlegs is deadly, the first question is which animal they mean. Two of the three cannot be venomous under any circumstances, because one of them is an insect and the other has no venom apparatus.

The venom claim, taken apart

Here is the myth in its standard form: daddy longlegs have the most toxic venom of any spider in the world, but their fangs are too short to penetrate human skin.

The Burke Museum, whose arachnology collection is the regional reference for exactly this question, calls it a full-fledged urban legend with no basis in fact whatever. That is the whole finding, and it is worth being precise about which parts of the claim fail and why, because the myth survives partly by being vague.

There is no toxicity measurement. UC Riverside’s spider research pages state plainly that there are no toxicological studies testing the lethality of pholcid venom on any mammalian system, and therefore no information is available on its likely effects. Nobody has ever ranked this spider’s venom against anything, because nobody has ever measured it. A superlative — the most venomous — requires a ranking, and the ranking does not exist.

What has been measured points the other way. The Burke notes a study finding pholcid venom unusually weak in its effect on insects. That is a study of prey, not of people, and it should not be over-read. But it is the only actual evidence in the vicinity of the claim, and it runs directly against it.

The fang argument does not hold either. The received version says the fangs are too short. UC Riverside’s response is that the brown recluse has a similarly structured fang and obviously does bite people, so fang architecture alone is not what decides the question — the musculature behind the fang is at least as relevant, and it has not been studied here either.

And there is no injury record. UC Riverside states there is no reference to any pholcid spider biting a human and causing any detrimental reaction. Penn State Extension’s own entry for the species says the same thing more bluntly: they are not known to be in any way harmful, and they do not bite people. Across the entire published literature, on a spider that lives in millions of houses across the northern hemisphere, there is no case.

What the television demonstration actually settled

Somebody always raises it, so it is worth handling directly rather than pretending it is not part of the conversation.

A popular science program tested the claim on air, got a pholcid to bite a human forearm, and reported a mild, brief sensation and nothing else. That episode is now cited in both directions: as proof that they can bite, and as proof that the venom is nothing.

What it demonstrated is narrower than either. It showed that under contrived conditions, on one occasion, a bite was possible and the outcome was trivial. It did not measure venom potency, it did not compare it against any other species, and one incident is not a toxicology study. A single anecdote cannot establish a superlative, which is exactly what the myth is.

The correct answer is not “it was disproved on television.” The correct answer is the one UC Riverside gives: there is no evidence this spider is dangerous to people, there never has been, and the claim that made it famous was invented rather than observed. That answer holds regardless of what any demonstration shows, and it is the version we would rather publish.

Recognizing one

The shape is unmistakable once you have seen it, and it is nothing like the other spiders that turn up indoors in this county.

Body. Small, pale, and elongated — Penn State gives females a body length of 7 to 8 millimeters and males around 6, in a pale tan or yellow with a gray mark in the center of the carapace. Held cylindrically, roughly like a grain of rice with legs.

Legs. The whole impression. The forelegs of an adult female run to about 50 millimeters — five centimeters of leg on eight millimeters of animal. They are thread-thin, pale, and move with a slow deliberate reach that looks nothing like the sprint of a funnel weaver.

Posture. Hanging upside down under the web, which is the single most reliable field mark. Nothing else common in a Whatcom County basement hangs inverted from a tangle.

Behavior when disturbed. Penn State describes it rapidly vibrating in a circular fashion in the web, which makes the spider harder to see. It is genuinely effective — a thin pale animal spinning in a gray tangle becomes a smear your eye cannot settle on.

The egg sac, if you catch one. The female wraps twenty-five to sixty eggs, each about a millimeter across, in a loose bundle of silk and carries the whole package in her mouthparts while hanging inverted. A cellar spider holding a ball of eggs in her jaws is one of the odder sights available in an ordinary garage.

Telling it from a giant house spider

These two share basements and garages across this county and they get reported to us in the same phone call, usually as “spiders in the crawlspace.” They are not remotely similar once you know what to look at, and the separation takes about two seconds rather than a microscope.

Leg thickness against body size. A cellar spider is a tiny pale body on hair-thin legs. A giant house spider is a substantial brown body on legs that are proportionally much shorter and visibly thicker, with hair on them. If the legs look like sewing thread, it is a pholcid.

Posture. Inverted under a tangle for the cellar spider, always. A funnel weaver sits the right way up, in a tube at the edge of a flat sheet, or runs across a floor.

Speed. A cellar spider moves slowly and reaches. A giant house spider crosses a room fast enough that people describe it as darting. Nobody has ever been startled by the movement of a pholcid.

The web. Loose three-dimensional tangle in an upper corner against a flat sheet with a funnel at one edge, low down. The web alone settles it without looking at the animal.

Where you find them dead. Giant house spiders end up trapped in bathtubs and sinks because they are poor climbers on glazed surfaces. Cellar spiders do not, because they are not walking the floor in the first place.

Both are harmless, so nothing about the identification changes your safety. What it changes is the advice, because the funnel weavers have a hard seasonal peak in late summer and this one does not have a season at all.

The web, and why it is such a mess

A cellar spider builds an irregular mesh of threads rather than a patterned structure. There is no wheel, no funnel, no sheet — just a loose three- dimensional tangle strung across a corner, under a joist, behind a water heater, over a basement window or across the angle where a wall meets a ceiling.

It is not a badly built web. It is a differently built one. Prey blunders into the tangle, gets caught in threads it cannot see, and the spider comes down its own lines to deal with it. Nothing about the arrangement needs to be tidy, and tidiness would cost silk for no return.

Two practical consequences follow.

The first is that these webs accumulate. Utah State Extension’s note on the group is that the webs collect dust and debris and become unsightly over time, and that is the entire complaint most households have. A cellar spider web is not taken down and rebuilt on a schedule the way an orb web is. It stays, collects everything in the air, and eventually reads as neglect even in a house nobody is neglecting.

The second is that clearing them is easy and lasting. A dry web that the spider is no longer maintaining comes away on a broom or a vacuum wand in one pass and does not reappear the next morning.

It hunts other spiders

This is the part that changes how the animal reads, and it comes straight from the extension literature rather than from folklore.

Utah State Extension lists cellar spider prey as insects and other arachnids, and files the group under beneficial. A cellar spider in a crawlspace corner is not sitting there decoratively. It is running a small predation program on whatever shares the space with it — flies, midges, small moths, gnats, and other spiders, including ones considerably heavier than itself.

The reach of those legs is what makes it possible. A pholcid does not close with prey the way a hunting spider does; it stays at the far end of its own limbs and throws silk from a distance, which is a workable way of dealing with something that could otherwise bite back.

So the household calculation on this species is genuinely lopsided. Removing them costs you a standing predator on the smaller arthropods in your basement and buys you nothing, because there was no risk to begin with. That is not an argument for keeping a web over the laundry sink. It is a reason to take down the webs that bother you and leave the ones in the crawlspace alone.

Where they live in this county

Cellar spiders are indoor animals here in a way that most spiders are not, and the local building stock decides where they turn up.

Older Bellingham housing — the Lettered Streets, Columbia, Sunnyland, York, Roosevelt, South Hill. Unfinished basements, post-and-pier crawlspaces and original utility runs give this species exactly what it wants: undisturbed corners, stable humidity, and a supply of small insects coming up out of the ground. This is where the heaviest populations in the county sit.

Attached garages, everywhere. The corner above the door track, the space behind stored boxes, the angle where the header meets the wall. A garage is warm enough, dark enough and left alone enough to suit them perfectly.

Crawlspaces, particularly damp ones. The population down there tracks the insect population down there, which tracks how wet the space is.

Sheds, pump houses, well houses and covered moorage around Blaine, Birch Bay, Semiahmoo and the rural blocks toward Lynden and Everson, where nothing disturbs a web from one season to the next.

Newer construction on the hill neighborhoods gets them too, just in fewer places — better sealing means fewer insects getting in, which means fewer spiders finding it worth staying.

Penn State’s note that both sexes remain active year-round in heated structures is the local detail that matters most. Unlike the funnel weavers, whose numbers spike visibly in autumn, cellar spiders do not have a season. They are simply there, all year, and how many you notice depends mostly on when you last looked behind the water heater.

The bite question, answered properly

For completeness, because people ask, and because the honest answer differs from the one the myth sets up.

There is no documented case of a cellar spider causing harm to a person. Penn State says they do not bite people; UC Riverside says there is no reference to a pholcid bite causing a detrimental reaction; the Burke calls the danger story an urban legend outright. Between them that is the entire literature, and it points one way.

The more useful warning is the one Washington’s health department attaches to spider bites generally: unexplainable wounds are often misdiagnosed as spider bites, and the misdiagnosis can leave the actual condition — frequently a bacterial infection — untreated. If you have a wound that concerns you, the right move is to see a physician about the wound rather than to look for a spider. We identify arthropods. Reading skin is not our work and we will not pretend otherwise.

The regional handbook produced jointly by WSU, Oregon State and the University of Idaho does not list this species among the Pacific Northwest spiders of any public health interest at all, which is its own kind of answer.

What to actually do

The honest version, in order of how much good it does.

Take down the webs you can see. A vacuum wand or a broom on an extension handle clears a garage in a few minutes, and because these webs are not rebuilt nightly the improvement holds. Do the corners, the joist bays, the window wells and the top of the door track.

Get the egg sacs while you are there. Removing a bundle of forty eggs in February is a great deal cheaper than dealing with the spiders it produces, and the sacs are easy to spot on a spider that carries them in her jaws.

Move what they are hiding behind. Stored boxes, stacked lumber, a spare refrigerator, a pile of tires. Undisturbed volume is most of what a cellar spider needs from a building.

Deal with the insects, not the spiders. Warm-toned or motion-sensor exterior lighting near doors, screens that actually seat, and a drier crawlspace all reduce the food supply, and the spider count follows the food supply down. Nothing you spray works as reliably as taking the prey away.

Close the low gaps. Door sweeps, the ends of sliding door tracks, foundation vent screens and utility penetrations. That is exclusion work, and it pays for itself against several unrelated problems at once.

Skip the fogger. UC IPM’s assessment of spider spraying is that control by spraying is only temporary unless it goes along with housekeeping, and that it is just as easy and much less toxic to crush the spider. That is a pest control authority telling you the product is the weaker option, and on this species we agree.

Our verdict, and what sits behind it

Rarely worth treating, and never worth treating for what the animal might do, because it does not do anything.

There are situations where the work is real. A garage, crawlspace or basement carrying years of accumulated webbing that somebody wants back. A seasonal property at Birch Bay or Semiahmoo that stood closed through the wet months and now has silk across every opening. A commercial site with a legitimate appearance standard. A household where somebody’s fear of spiders is shaping how they use their own home, which is a real problem and not a trivial one.

All four of those are cleaning and exclusion jobs with a spider attached. We are happy to do them and we would rather call them what they are.

What we will not do is sell a treatment program against a beneficial spider on the strength of a venom story that the Burke Museum classifies as an urban legend. The regional handbook’s line on spiders in general is that it is rarely useful to apply pesticides or fumigate a house to control them, and that pesticides do not provide long-term control because surrounding spiders recolonize. That applies here with more force than usual, because this particular spider was on your side.

If you want it identified

Send a photograph. A shot from the side showing the body against the legs is enough, and a coin or a fingertip in the frame settles the scale question that long legs make so confusing.

The three things we will tell you: whether it is a cellar spider, a harvestman or something else entirely; whether anything about it warrants concern, which on this species it does not; and what, if anything, is worth doing about the corner it was sitting in. That conversation is free and it very often ends with a recommendation to leave the spider where it is.

Related work

The other spider that shares a crawlspace with this one is the giant house spider, which is larger, faster and also harmless. Our general position on spiders, including why spraying does less than people expect, is on spider control. If the crawlspace under the house is what is producing the insects that feed everything down there, the durable fix is crawlspace cleanout and restoration, and closing the low gaps that let it all in is exclusion and repairs.