Long Bodied Cellar (Pholcus phalangioides)

Physical description and identification

Almost everything people notice about Pholcus phalangioides is leg. The body is smaller than a grain of rice, pale and semi-transparent, and hangs motionless at the centre of a span of hair-thin limbs that can cover a palm.

Adults

• Size: females measure roughly 8–10 mm in body length, males about 6–7 mm. The leg span reaches around 7 cm (2.7 in), with the first pair of legs up to five times the body length — one of the most extreme leg-to-body ratios of any house spider.
• Colour: translucent yellowish-brown to pale grey with fine grey hairs, a large greyish blotch in the middle of the carapace and faint darker chevrons showing through the abdomen wall.
• Eyes: eight, but nothing like the two neat rows of a hunting spider. Six form two raised groups of three on either side of the head, with a small pair close together in front — a layout shared across the family. See our guide to spider eyes.
• Distinctive features: the abdomen is cylindrical and about three times longer than wide, quite unlike the globe-shaped abdomen of most house spiders. The legs end in a flexible, finely divided tarsus that curls around a single thread. Mature males are slimmer, with swollen pedipalps and forward-projecting jaws.

Eggs and egg sacs

A female binds her eggs in so little silk that they stay visible through the covering, then carries the bundle in her jaws — in the chelicerae, not the pedipalps, a detail frequently reported wrongly. She cannot feed while carrying it. A clutch holds 13 to 60 eggs, a female produces about three clutches in her life, and they hatch in two to three weeks.

Spiderlings

Hatchlings are colourless and almost invisible, with legs still short in proportion to the body. They stay clustered in the mother's web for several days before scattering. Over five or six moults the legs lengthen much faster than the body, so adult proportions appear only at the end. Shed skins hang in the web for weeks and are often mistaken for dead spiders.

The web

The web is a loose, untidy three-dimensional tangle with no radial pattern and no sticky droplets. It works mechanically: an insect blunders into the scaffolding, the threads collapse around it, and the spider — hanging upside down underneath — throws more silk over it from a distance with the combs on its hind legs, biting only once the prey is immobilised. Cellar spiders never eat old silk or rebuild, so the structure accumulates layers and dust. See our guide to spider webs.

Where the long-bodied cellar spider lives

Pholcus phalangioides is genuinely cosmopolitan: established on every continent except Antarctica, and one of the commonest indoor spiders of Europe, North America, Australia, New Zealand, southern Africa, Asia and South America alike. Older accounts listing only Asia, Europe, Africa and South America miss most of its range. Its native range is not known with certainty; the usual assumption of an Old World subtropical origin is an inference, not a documented fact. The modern distribution is the work of human trade, and one fertilised female can found a population in a new building.

The species is limited by cold rather than geography. It cannot survive freezing and becomes inactive below roughly 8 °C, so across most of its range it lives strictly indoors: cellars, crawl spaces, garages, sheds, barns and undisturbed ceiling corners. In warm-winter regions such as the Mediterranean and California it also uses caves, rock overhangs and shaded outer walls. It is the most familiar member of the cellar spider family and among the most reliable of all house spiders, preferring darkness, still air and humidity — which is why a damp basement holds more of them than a heated living room.

Are long-bodied cellar spiders venomous? The daddy-long-legs myth

Yes — like nearly every spider, Pholcus phalangioides has venom glands and uses venom to subdue prey. The real question is the one everybody asks: is the daddy-long-legs the most venomous spider alive, saved from being lethal only by fangs too short to break skin? No. The claim fails on both halves, for the same reason: nobody tested it before repeating it.

• The venom is not exceptionally potent. No study has ever shown pholcid venom to be unusually toxic to mammals, and the evidence points the other way: it acts on insects and contains nothing comparable to the neurotoxins of widow spiders or the tissue-damaging enzyme of a brown recluse. The species belongs nowhere near a list of the most venomous spiders.
• The fangs can penetrate skin. Pholcid fangs are short, around a quarter of a millimetre — but so are a brown recluse's, and that spider bites people readily. The arachnologist Rick Vetter made the point for years, and in 2004 MythBusters tested it: a cellar spider was induced to bite a human forearm, and it did. The result was a brief, faint burning sensation that faded within seconds, with no swelling and no mark.

The honest summary is the unglamorous one: the venom is weak, the bite is trivial, and the fangs are not what is protecting you.

Can long-bodied cellar spiders bite?

They can, and it hardly ever happens. The spider is fragile, slow to leave its web and quick to drop on a dragline or spin into a blur when threatened; biting is far down its list of responses. The few documented bites describe a small pinch or a momentary sting, sometimes with a trace of redness, gone within an hour. There is no necrosis, no systemic illness and no antivenom, because none is needed. Pets are in no danger either.

If you are bitten, wash the site with soap and water and apply a cold pack if it is sore. Nothing else is required. Watch for spreading redness or unusual swelling, which points to an ordinary skin infection or an allergic response rather than the venom, and seek medical advice if that happens. Keep the spider or a photograph, since most anxiety about indoor bites comes from misidentification.

Ecological importance and behavior of the long-bodied cellar spider

The long-bodied cellar spider is a patient, web-bound predator with an unusual speciality: it eats other spiders. It walks into a neighbouring web, plucks the silk with its front legs in a rhythm that imitates a struggling insect, and attacks the resident when it comes to investigate. This is aggressive mimicry, and it works on species much heavier than itself — house spiders, funnel weavers such as the giant house spider and, in trials, even widow relatives like the redback. The long legs are the key: they deliver silk and a bite from beyond a shorter-legged opponent's reach. The rest of the diet is ordinary indoor fare — mosquitoes, midges, flies, moths, woodlice, silverfish and ants.

Defensive whirling: touched or threatened, the spider braces its legs and gyrates so fast that its body becomes a blur, then stops abruptly. The effect breaks a predator's visual lock, and most of the family does it.

Natural predators: other pholcids, including larger individuals of its own species, are the main threat, and cannibalism is routine. Jumping spiders hunt them inside their webs, and parasitoid wasps, centipedes and geckos take them where ranges overlap.

Seasonal behaviour: indoors the species barely has a season. Adults, juveniles and egg-carrying females turn up in any month, with a mild peak in late summer. Females live around two years, occasionally three.

Relationship with humans: harmless and beneficial. If webs are unwelcome, a vacuum removes silk and spiders in one pass; insecticide is pointless, since new individuals walk back in within weeks.

Similar spiders and the other daddy-long-legs

Quick facts

Did you know?

• The species was described in 1775 by the Swiss naturalist Johann Caspar Fuesslin, making it one of the earliest named of all house spiders.
• The grey mark on the carapace, with two dark pits where the eye groups sit, suggests a tiny human skull — hence the nickname skull spider.
• Because it hunts other spiders in their own webs, a cellar spider population can gradually clear a building of larger species that people find far more alarming.
• The finely divided leg tips are an adaptation for a loose tangle: the spider grips single threads rather than a surface, and is clumsy on the ground.

In summary, the long-bodied cellar spider is a harmless, long-lived and effective indoor predator wrapped in a reputation it never earned. The venom is weak, the bite is a non-event, and the genuinely remarkable thing about it is what it does to the other spiders in your basement.