Eratigena

Physical description and identification

Eratigena is a genus of large, fast funnel weavers in the family Agelenidae. It did not exist before 2013, when Bolzern, Burckhardt and Hänggi revised the European Tegenaria group using anatomy and DNA, found one cluster of species sitting well apart from the rest, and moved it into a new genus named Eratigena — an anagram of Tegenaria. Around twenty species are recognised, most Mediterranean, and two are famous: the giant house spider and the hobo spider.

Adults

• Size: the genus spans a wide range. The giant house spider (E. atrica) has a body of about 15–18 mm and a leg span approaching 7 cm, making it one of the largest spiders Europeans see indoors. The hobo spider (E. agrestis) is much smaller at roughly 7–14 mm. Females are consistently larger than males.
• Colour: brown is the rule, from sandy tan to deep chocolate, with the pattern doing the work rather than the colour. Most species carry a row of pale chevrons down the abdomen and two indistinct darker bands on the carapace.
• Eyes: eight small eyes of similar size in two short rows of four. No pair is enlarged, which separates the genus immediately from wolf spiders, the group it is most often mistaken for.
• Distinctive features: long posterior spinnerets projecting past the abdomen; dense hair on the legs, palps and body in the giant house spider; a narrower, oblong abdomen in the hobo. The teeth along the fang furrow differ between species and are one of the characters specialists count. Identification to species needs an adult and a microscope.

Eggs and egg sacs

A female wraps her eggs in a dense white silk sac, typically containing between about 60 and 100 eggs, and keeps it inside or beside her retreat rather than out on the open sheet. Sacs are produced from late summer into autumn, and a female that survives the winter in a building may make more than one.

Spiderlings

Spiderlings hatch as miniature adults, pale and long-legged, and grow only by moulting — several times before maturity. They disperse on foot along silk lines rather than by ballooning, which is one reason these spiders build up in a single building over years instead of spreading quickly across a landscape.

The web

Every species builds the same structure: a flat, untidy sheet of dry silk with a tubular funnel at one edge leading into a crack or a hole in a wall. The silk carries no glue. It works as a vibration sensor and a stumbling field, and the spider does the rest, sprinting out to grab whatever has fallen onto it. Sheets are added to rather than rebuilt, so an old web in a garage corner is a thick grey mat. See our guide to spider webs.

Where Eratigena spiders live

The genus is native to the western Palearctic: Europe, North Africa and parts of Central Asia, with the greatest species richness around the Mediterranean. Claims that Eratigena occurs across Africa generally overstate the case — the African records are North African, not tropical. One species, E. laksao, is known from Southeast Asia.

Two species have crossed the Atlantic in cargo. The hobo spider reached the Pacific Northwest in the first half of the twentieth century and is now common in Washington, Oregon and British Columbia; the giant house spider group arrived in the same region and has largely displaced it indoors. In Britain and much of northern Europe the giant house spiders are the classic autumn "spider season" animal.

Habitat is consistent: a dark, dry cavity beside an open surface. Indoors that means garages, cellars, sheds, wall voids and the space under stairs; outdoors, rock piles, dry-stone and retaining walls, log stacks and cave entrances. The hobo spider is far more an outdoor animal than its reputation suggests, while the giant house spiders are among the most familiar of all house spiders.

Are Eratigena spiders venomous?

Yes, and like nearly all spiders they use that venom on insects. No Eratigena species is medically significant to humans. This matters because the hobo spider spent three decades being described as dangerous: from the late 1980s it was blamed for necrotic, slow-healing skin wounds in the Pacific Northwest. That claim never survived scrutiny. Laboratory work failed to reproduce tissue damage, no comparable effect is reported from the species' native Europe, and in 2017 the United States Centers for Disease Control removed the hobo spider from its list of venomous spiders. Older articles calling the hobo's bite "painful but not venomous" err in the opposite direction: the spider is venomous, its venom simply does not harm people.

Can Eratigena spiders bite?

They can, and the fangs of a large female giant house spider are long enough to pierce skin — but it takes real provocation. These are timid, web-bound animals whose reflex is to bolt into the funnel, and documented bites involve a spider trapped against skin in clothing, bedding or a glove.

A bite feels like a sharp pinch, leaves a small red mark and may itch or swell mildly for a day or two. Wash it with soap and water, use a cold pack and keep the site clean. Seek medical advice if pain worsens over several days or the area becomes hot and spreading, which indicates a skin infection rather than venom. There is no antivenom for any Eratigena, because none is needed.

The hobo spider's name is another source of trouble. Agrestis means "of the fields", not "aggressive", and the species is no more prone to biting than its relatives.

Ecological importance and behavior of Eratigena spiders

Eratigena spiders are nocturnal ambush hunters that spend the day in the retreat with their front legs on the silk. The sheet transmits the footfall of anything that lands on it, and the spider crosses it at remarkable speed. The diet is broad and almost entirely insect: flies, moths, beetles, earwigs, ants and woodlice. Older accounts listing wasps and other spiders as the staple describe occasional prey, not the norm.

Natural predators: spider-hunting wasps and mud daubers, which stock their nests with paralysed spiders, along with centipedes, ants, cellar spiders, birds, shrews and lizards. Wandering males are by far the most vulnerable.

Prey-predator dynamics: the sheet sits low down against a vertical surface, a level few other web builders use, so a row of Eratigena webs along a wall works as a continuous insect filter. Where two species overlap indoors the larger wins: giant house spiders prey on hobo spiders, which is one reason hobo numbers are lower inside buildings than outside them.

Seasonal behaviour: males mature in late summer and abandon their webs to search for females through autumn, which is why so many large spiders appear in European houses in September and October. Males die within weeks of mating; females may live two to three years, longer in an undisturbed indoor site.

Relationship with humans: beneficial and essentially risk-free. Removing a web and sealing the crevice behind it works better than any spray, and a wandering male is easily caught under a glass.

Species in the genus and similar spiders

Quick facts

Did you know?

• The genus name is a deliberate anagram of Tegenaria — the authors of the 2013 revision built the joke into the nomenclature.
• A giant house spider once held the record as the fastest-running spider ever measured, clocked at roughly half a metre per second over a short burst, a speed it needs because its web has no glue in it.
• The autumn wave of large spiders in British and Irish houses is almost entirely mature Eratigena males on the move, not an invasion and not a population boom.
• Giant house spiders eat hobo spiders, so the arrival of the larger species in North American buildings pushed the hobo back out to walls and rockeries.

In summary, Eratigena is a young genus with an old history: European funnel weavers that were called Tegenaria for two centuries and were reclassified in 2013. They are big, fast and startling, and they are also harmless — the scariest thing about them is the reputation the hobo spider was given by mistake.