House Spider, Giant House Spider, or Something Else?

Four different animals get called a house spider, they are not closely related, and confusing them is why the question "is this dangerous" gets such inconsistent answers.

Start with where it is and what it is sitting in.

The four

Common house spider (Parasteatoda tepidariorum) — small, 5–8 mm, mottled brown, with a globular abdomen and thin legs. Hangs upside down in an untidy tangle web in a corner, behind furniture, in a window frame. This is the one making the cobwebs.

It is a cobweb spider, in the same family as the widows, which is why the web looks similar and why people worry. The body is mottled brown rather than glossy black, and there is no marking underneath.

Giant house spider (Eratigena atrica) — large, body 12–18 mm with a leg span that can reach 75 mm. Brown, hairy, fast. Builds a flat sheet web with a tube retreat in a garage, shed, cellar or wall gap, and is the animal most often found running across a floor in autumn or stuck in a bath.

Southern house spider (Kukulcania hibernalis) — southeastern United States. Females are large, dark, velvety and live for years in a crevice with a distinctive radiating tangle of silk around the entrance. Males are lighter brown, long-legged, and wander — and they are frequently reported as brown recluses.

Cellar spider (Pholcus phalangioides) — very long thin legs, small body, hanging in a loose web in a ceiling corner. Vibrates rapidly when disturbed. Called daddy long-legs, along with two entirely different animals, and the subject of the most repeated falsehood in the whole subject — the daddy long-legs myth.

Telling them apart

The web does most of the work here, which is generally true — identifying a spider by its web covers the four architectures and what each one rules out.

The one worth a second look

None of the four. But the common house spider shares a family and a web type with the widows, so the tangle web in a dark void is the one situation where a proper look is worth it.

The separation is the abdomen and the underside: a widow's abdomen is a smooth glossy sphere with a red or orange marking beneath, and a house spider's is mottled brown with nothing. Black widow or common house spider has the full set.

False widows (Steatoda) sit between the two and cause a good deal of alarm, particularly in Britain. Glossy, dark, with a globular abdomen and often a pale crescent or skull-like marking on top — but never the hourglass underneath. Their bite is comparable to a wasp sting.

The hobo spider question

In the Pacific Northwest the giant house spider and the hobo spider live in the same buildings and are separated by microscopic examination of the genitalia. Neither can be identified from a photograph, and every field character offered for the hobo has turned out to be unreliable.

That would matter if the hobo were dangerous. On the current evidence it is not — the claim rested on a small number of unreplicated studies and the CDC removed the species from its list in 2017, which is set out in the hobo spider was never dangerous.

So the practical answer in that region is that a large fast brown funnel weaver is a large fast brown funnel weaver, and it does not matter which.

The autumn ones

Most large house spiders seen in the open are mature males walking in search of females, between late August and early October. They have been in the building all year and are not coming in from the cold — why there are suddenly spiders everywhere.

Which also means they are not evidence of an infestation, of a gap in the building, or of anything about the house. It is a calendar effect.

Getting one out

A glass and a piece of stiff card, and a garage or shed rather than the garden — house spiders are indoor animals in much of their range and an October night outside is often fatal. Getting a spider out of the house without killing it has the method, including for the large ones.