Giant House (Eratigena atrica)

Physical description and identification

The giant house spider is a big, hairy, long-legged funnel weaver in muted browns. Size is the first thing anyone notices, but the useful features are the mottling on the legs and the pair of long spinnerets that stick out behind the abdomen like a short tail.

Adults

• Size: females measure about 12–18 mm in body length, males 10–15 mm. Female leg span is around 45 mm; the longer-legged males can reach 75 mm (roughly 3 in), which is why the males that wander in autumn look so much bigger than the females sitting in the webs.
• Color: beige, brown or orange-brown overall. The sternum carries a row of about three paler dots down each side, and the abdomen has a chevron pattern with roughly six paler spots along each flank. Legs and palps are hairy and marked with darker mottling or faint bands.
• Eyes: eight eyes of similar size arranged in two rows. They form only crude images — enough to register light, shadow and movement — so the spider identifies prey by vibration rather than sight. Our guide to spider eyes explains why web-builders invest so little in vision.
• Distinctive features: the long posterior spinnerets are visible from above and are a family trait of the funnel weavers. Mature males have swollen pedipalps and disproportionately long legs; females are heavier and shorter legged.

Eggs and egg sacs

Females build lens-shaped white egg sacs, typically containing about 40–60 eggs, and fasten them in or beside the funnel retreat. Several sacs may be produced over a female's long life. She guards them and remains with the web rather than dispersing.

Spiderlings

Hatchlings are pale and stay clustered near the sac for around a month before spreading out. Each then needs a long series of molts — commonly eight to ten — spread over one to two years before reaching maturity, which is why houses hold spiders of every size at once.

The web

The web is a broad, flat sheet of tightly woven silk, opaque white when new, that narrows at one end into a tube. The spider sits in the tube with its front legs resting on the sheet. The silk has no glue at all: it works by tripping and tangling insects long enough for the spider to cross the sheet and bite. Webs are wedged into the angles of walls, behind furniture, in cupboards, lofts, sheds and garages, and outdoors in cavity walls, log piles and rock crevices. The silk is added to rather than replaced, so an undisturbed web becomes a thick grey mat over months. See our overview of spider webs for how sheet webs differ from sticky orbs.

Where giant house spiders live

Eratigena atrica and its close relatives are native to western and central Europe, and the group is one of the most familiar elements of the household fauna across Britain, France, the Low Countries and neighbouring countries. It has been carried to North America and is now well established in the Pacific Northwest — Washington, Oregon and British Columbia — as well as in parts of eastern Canada.

The habitat is exactly what the name suggests: buildings. Cavity walls, lofts, cellars, garages, sheds, outbuildings and the backs of cupboards all suit it, and it tolerates dry indoor air better than most large spiders. It also lives perfectly well outdoors in log piles, hollow trees, rock crevices and cave entrances, so garden populations continually resupply the ones indoors. Older accounts describing it as a spider of dry-forest caves capture only the wild end of a range that is overwhelmingly synanthropic.

Are giant house spiders venomous?

Yes, and harmlessly so. Like every member of the family it carries venom for subduing insects, dominated by small peptides of the agatoxin type that act on invertebrate ion channels. Those molecules are potent against flies and moths and have no meaningful activity against mammals at the doses involved.

The giant house spider is not related to the widow spiders, has no dermonecrotic enzymes of the kind recluses carry, and appears on no list of medically important species anywhere in its range. Despite being one of the most frequently encountered large spiders in European homes, it has never accumulated a record of serious bites — which, given how many millions of encounters happen each autumn, is the strongest evidence available.

Can giant house spiders bite?

It can bite, and unlike many smaller house spiders its fangs are long enough to pierce human skin — but it very rarely does. A giant house spider's response to a person is to freeze and then run. Bites are recorded almost exclusively when the spider is squeezed: trapped in clothing, caught under a hand, or held.

The result is a brief sharp pain, sometimes compared to a bee sting, with mild local redness and swelling that typically settles within a couple of hours and always within a day or two. There is no tissue destruction, no systemic illness and nothing to treat beyond comfort.

Wash the area with soap and water, use a cold pack for soreness, and keep it clean. Seek medical advice only if the area becomes progressively hot, red and painful over following days, discharges pus, or is accompanied by fever — that indicates a bacterial skin infection rather than venom. If you can safely retain the spider or photograph it, do so; correct identification prevents a great deal of unnecessary worry.

Ecological importance and behavior of the giant house spider

This is a nocturnal ambush predator with an exceptionally sedentary lifestyle. A female may spend years in a single corner, enlarging her sheet and emerging only to seize prey: flies, blowflies, moths, wasps, woodlice, silverfish and other spiders, including smaller funnel weavers.

Natural predators: birds, spider-hunting wasps, centipedes, shrews and cats indoors. Cellar spiders sharing the same buildings are capable of killing much larger spiders, giant house spiders among them.

Prey-predator dynamics: in the Pacific Northwest the species is also a competitor and predator of the introduced hobo spider, and its spread through the region appears to have reduced hobo numbers in houses. Indoors, a few established webs measurably suppress fly and moth populations.

Seasonal behavior: the reason for "spider season" is simple — mature males abandon their webs from late August to October to search for females, and a male that falls into a bath or sink cannot climb the smooth sides and is found stranded the next morning. Males die within weeks of mating; females are long-lived, commonly two to three years and occasionally far longer.

Relationship with humans: entirely beneficial. The spider needs no control and providing an escape route from smooth-sided baths — a towel over the edge — solves the only real problem it causes.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The giant house spider once held the Guinness World Record for the fastest spider, clocked at about 1.18 mph (0.53 m/s) — a speed it can only hold for a second or two before it has to stop and recover.
• The genus name Eratigena is an anagram of Tegenaria, the genus these spiders were moved out of in a 2013 revision of the European funnel weavers.
• "Giant house spider" covers a taxonomic argument. Three forms long treated as separate species — atrica, saeva and duellica — were merged under Eratigena atrica in 2013, and later work using morphology and DNA argued for splitting them again. It is safest to speak of the Eratigena atrica group.
• The autumn invasion is not spiders coming in from the cold. Most were born in the building or its walls; what changes in September is that the males stop hiding and start walking.

In summary, the giant house spider is a large, fast, long-lived and completely harmless predator that has shared European buildings for centuries and now does the same in the Pacific Northwest. Learn the mottled legs, the sheet-and-funnel web and the autumn wandering males, and the biggest spider in the house stops being frightening.