Giant House Spider (Eratigena atrica): Facts, Size and Speed

What is a giant house spider?

The giant house spider belongs to the family Agelenidae, the funnel weavers, named after the funnel-shaped retreat at the back of their webs. It was long placed in the genus Tegenaria, and many older books still call it Tegenaria atrica or Tegenaria gigantea. In 2013 it was moved to the new genus Eratigena, a name made by rearranging the letters of Tegenaria.

The name “giant house spider” actually covers three very similar species: Eratigena atrica, E. duellica and E. saeva. For a time they were treated as one species. A 2018 study of their anatomy and genetics found small but consistent differences, and the three were restored as separate species, a view accepted by the World Spider Catalog in 2020. They can only be told apart under a microscope, by the shape of the male palps and the female genital openings, so in everyday use all three are simply “giant house spiders”.

Appearance

The giant house spider is dark brown to reddish or yellowish brown, with long, hairy legs. The front part of the body (the cephalothorax) has darker bands, and the abdomen shows a pale stripe down the middle with a row of lighter spots on each side. Underneath, the breastplate carries a pale arrow-like marking of three spots on each side.

Males and females look alike in color, but adult males have a slimmer abdomen, even longer legs and swollen pedipalps, the short, leg-like organs near the mouth that they use for mating. They look like a pair of small boxing gloves.

Like other funnel weavers, the giant house spider has eight eyes of equal size in two rows. Its vision is poor: it probably distinguishes little more than light and dark. It senses prey and danger mainly through vibrations in its web and the hairs on its legs.

How big is a giant house spider?

The giant house spider is among the largest spiders in Central and Northern Europe, and it often looks bigger than it is because of its long legs.

Spider weights are rarely measured, but even large females weigh well under a gram. For truly heavy spiders, see the largest spiders in the world.

How fast is the giant house spider?

The giant house spider is one of the fastest-running spiders known. A figure of about 0.5 m/s (1.7 ft/s), roughly 1.9 km/h (1.2 mph), comes from a measurement made decades ago and long listed by Guinness World Records as a spider speed record. It is an old, single figure rather than the result of systematic testing, but it fits the experience of anyone who has seen one dash across a room.

Relative to its body size the speed is remarkable: at that rate a spider with an 18 mm body covers well over 25 body lengths a second. It cannot keep it up for long, though. Like many spiders, giant house spiders run in short bursts and then pause, partly because their breathing system cannot supply oxygen fast enough for long runs.

Habitat and range

Giant house spiders are native to Europe. In the wild their original habitats are caves, rock crevices and dry woodland, where they build webs under stones and in hollows. Today they are best known from buildings, including houses, cellars, sheds, garages, attics and barns, especially in dark, rarely disturbed corners.

The group was accidentally introduced to the Pacific Northwest of North America around 1900 and has increased greatly since. E. duellica is now widespread in Washington, Oregon and British Columbia, while E. atrica itself has been recorded in British Columbia, Montana, Quebec, Newfoundland and Nova Scotia. In Europe the species has also turned up in countries where it was not previously recorded, such as the Baltic states.

Webs and diet

The giant house spider builds a flat, untidy sheet web with a funnel-shaped retreat at one end. The silk is not sticky. Instead, the sheet works as a tripwire and tangle: when an insect walks or lands on it, the spider feels the vibrations, races out of the funnel, bites the prey and carries it back into the retreat.

Common prey includes flies, beetles, moths, woodlice and other spiders, more or less anything small that crosses the web. Like nearly all spiders it uses venom to subdue prey and digestive fluids to liquefy it. Webs are typically built in corners at floor or ceiling level, between boxes, behind furniture and near windows. For more on spider food in general, see What do spiders eat?.

Behavior and seasons

For most of the year giant house spiders go unnoticed. Females and young spiders rarely leave their webs except to catch prey. The change comes in late summer: from about July to October, adult males leave their webs and wander, sometimes for long distances, in search of females.

These wandering males are the spiders that appear in bathtubs, run across carpets at night and give rise to talk of a “spider season” in Britain and Northern Europe. They are not moving in from the cold; most were already living indoors. The full story is in Why do spiders come indoors in the fall?.

Spiders found in bathtubs have not usually climbed up the drain. More often they have fallen in while wandering and cannot climb the smooth, steep sides.

Reproduction and lifespan

When a male finds a female’s web, he signals his presence by plucking and tapping the threads. The female’s silk and body carry chemical signals that help males recognize her. Males may stay with a female for some time and mate several times, and they usually die within weeks or months afterward. Some are eaten by the female.

The female wraps her eggs in a silk sac, which she hides in or near her web. At least 60 spiderlings can emerge from one sac. Unusually for spiders, the young stay together for about a month, sharing the web without cooperating to catch prey. They molt seven or eight times before reaching adulthood.

Giant house spiders usually live two to three years, which is long for a European spider, and lifespans of up to six years have been recorded. Females live longer than males. Compare other species in How long do spiders live?.

Is the giant house spider dangerous?

No. Giant house spiders are not considered dangerous to people or pets. They are reluctant to bite and prefer to freeze or run away. Their fangs can pierce human skin, so a bite is possible if a spider is pressed against the body, but the usual result is local pain and swelling that soon passes. See Are house spiders dangerous? for the bigger picture.

Predators, look-alikes and relationship with people

In houses, giant house spiders are hunted by the long-legged cellar spider (Pholcus phalangioides), which raids other spiders’ webs. Outdoors, birds, shrews, spider-hunting wasps and other spiders take them.

The giant house spider is often confused with the smaller barn funnel weaver or domestic house spider (Tegenaria domestica) and, in North America, with the hobo spider (Eratigena agrestis). The hobo spider is smaller, with a body of no more than about 15 mm (0.6 in). It was once blamed for serious bites in the Pacific Northwest, but later research found no good evidence for this. Some people suggest that giant house spiders may compete with hobo spiders where both occur.

The giant house spider has not been assessed by the IUCN. It is common across its range and benefits from living alongside people, eating flies and other insects in homes and outbuildings.

Myths and facts

Myth: house spiders move indoors when it gets cold. Giant house spiders are a house-dwelling species that lives indoors all year. The ones seen in autumn are males that have left their webs to look for mates, not outdoor spiders seeking warmth. Most outdoor spiders would not survive long in a dry, heated house.

Myth: house spiders crawl up through the plughole. Bathroom drains have water traps that spiders cannot easily get through. A spider in the bath has almost always fallen in from above and is unable to climb back out over the smooth enamel.

Myth: a big, fast spider must be dangerous. Size and speed say little about venom. The giant house spider’s venom is adapted to insects, and it would much rather run than bite. In Europe and North America, the spiders of real medical interest are a few quite different species, such as widow spiders and recluse spiders.

Fact: they are useful lodgers. By catching flies, moths, woodlice and other spiders, giant house spiders act as a natural check on small invertebrates in sheds and cellars, and a single female can occupy the same quiet corner for years.

Fact: they are among Europe’s speediest spiders. The old record speed of about 0.5 m/s (1.7 ft/s) is still widely quoted, and in sprints this spider covers many times its own body length each second.