Grey House (Badumna longinqua)

Physical description and identification

The grey house spider is a compact, thick-legged spider that almost never leaves its web. Usually only the front half of it shows: the female sits in the mouth of her silk tube with the rest of her body pushed into the crevice behind it, and she vanishes the moment the sheet is touched. The web is often easier to identify than the spider.

Adults

• Size: females, the ones people find, have a body length of about 10–14 mm (0.4–0.55 in) and a leg span approaching 30 mm. Males are slimmer and smaller at 8–10 mm, with proportionally longer legs and swollen tips on the pedipalps.
• Colour: the carapace and legs are dark grey-brown to purplish brown under a dense coat of short grey hairs, which gives the whole spider a dusty, velvety look. The abdomen is charcoal to ash grey with paler paired patches and faint chevrons running back toward the spinnerets, and each leg segment shows darker rings and rows of stiff hairs.
• Eyes: eight small dark eyes in two short rows of four, all close to the same size. Older popular accounts claim the front pair is enlarged; no eye on a Badumna is noticeably bigger, and that absence of two large forward-facing eyes is what rules out a similarly grey jumping spider.
• Distinctive features: a cribellum, the flat plate of silk spigots in front of the spinnerets, and a calamistrum, the comb of curved bristles on the hind legs that teases that silk into a woolly ribbon. This is what makes a fresh web look bluish and fuzzy.

Eggs and egg sacs

The female wraps batches of pale round eggs in loose, disc-shaped white sacs fixed inside the retreat rather than out on the open sheet. She produces several over the warm months and stays with them, so the sacs are rarely seen.

Spiderlings

Hatchlings are pale and translucent, darkening to adult grey over several moults. They stay briefly in the mother's web, then leave as very small spiderlings, walking off along draglines or ballooning a short distance on a thread. Dispersal happens while they are juveniles, not at maturity — the common claim that they leave on maturing reverses what happens. Young that settle nearby build their first webs along the same wall, which is why the webs appear in clusters.

The web

The web is not a ladder and it is not an orb. It is an irregular lacy sheet of cribellate silk, typically 15–25 cm across, with a funnel-shaped tube at one edge running back into a crack, a window frame corner or a hollow in rough bark, and signal lines radiating across the sheet. The hackled silk is dry rather than glue-coated: its combed nanofibres snag insect bristles and claws, so it works like felt instead of flypaper. New webs are bluish-white; old ones grey off and collect dust. See our guide to spider webs for how this differs from a sticky orb.

Where the grey house spider lives

Badumna longinqua is native to eastern Australia, from Queensland south through New South Wales and Victoria. It travels well in shipping containers, timber, garden pots and on vehicles, and it is now common throughout New Zealand, widespread in Japan, established along the Pacific coast of North America — California, Oregon and Washington in particular — and recorded from Mexico, Uruguay, Argentina and Brazil, with scattered European introductions.

Its habitat is vertical and sheltered: rough surfaces with a crack behind them. Tree trunks, rock faces, brick walls, fence palings, water meters, window frames, guttering and the gaps around outdoor light fittings all qualify, and lighting helps, because moths drawn to a porch light stumble into a web built beside it. Older accounts listing wetlands, riparian forest and grassland describe the countryside the species occurs in rather than where it builds. This is an edge-and-crevice spider, abundant on the outside of buildings but rarely found indoors.

Are grey house spiders venomous?

Yes, in the same sense as almost every spider: it has venom glands and uses them on insects. It is not medically significant to people or pets, there is no antivenom and none is needed, and no serious envenomation has been confirmed. It is not related to the widow spiders, the recluses or the Australian funnel-webs, and it lacks the neurotoxins and tissue-damaging enzymes that make those groups dangerous. Its venom is a fast-acting insect toxin delivered by short fangs poorly suited to human skin.

Can grey house spiders bite?

A grey house spider can bite, but it is a poor candidate for it: its reaction to a hand or a broom is to bolt into the retreat. The realistic scenarios are pressing on a spider hidden in folded outdoor furniture or garden gloves, or grabbing a wandering male that has ended up in bedding in late summer.

Reported bites cause immediate local pain out of proportion to the tiny fang marks, sometimes with brief redness and mild swelling that fades within a day. Wash the site, apply a cold pack and take a simple painkiller if needed. Seek medical advice if the pain escalates or swelling spreads, which points to an allergic reaction or a secondary infection rather than to the venom itself.

Ecological importance and behavior of the grey house spider

The grey house spider is a sit-and-wait predator with an unusually strong attachment to its own web. It rests in the tube by day, sits at the mouth after dark with its front legs on the signal lines, and rushes out when a vibration tells it something has landed in the sheet. Prey is whatever the wall produces: moths, flies, ants, small beetles, bees and wasps, plant hoppers and psyllids.

Natural predators: the most important is the white-tailed spider, a webless hunter that specialises in invading Badumna webs and eating the resident. Parasitoid wasps provision their nests with adults, parasitic flies attack the egg sacs, birds and geckos take exposed spiders, and indoors cellar spiders catch wandering males. Some older accounts list a New Zealand short-tailed bird as a predator; no such bird exists, and the reference appears to garble New Zealand's lesser short-tailed bat, which does forage on the ground for invertebrates.

Prey-predator dynamics: the vertical sheets sit above the ground-level mesh of the hacklemesh weaver and below the aerial orbs of garden orb weavers, so they intercept a different set of insects. In New Zealand the species is now more abundant on buildings than most native spiders.

Seasonal behaviour: adults occur all year in mild climates. Mature males leave their webs in late summer and autumn, mate at the mouth of the female's tube and die within weeks, while females may breed through two seasons. Juveniles grow by moulting, and cast skins collect in the retreat beside the husks of past meals.

Relationship with humans: harmless and useful. If a web is unwanted, brushing it off and sealing the crack behind it is enough; insecticide is unnecessary, and an untreated wall is recolonised within weeks.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The species was described in 1867 by the German arachnologist Ludwig Carl Christian Koch, originally in a different genus; it was later moved to Badumna, erected by the Swedish arachnologist Tamerlan Thorell in 1890.
• Badumna spent most of the twentieth century in the family Amaurobiidae before being placed in Desidae, a family that also contains the true intertidal spiders of the genus Desis — although the grey house spider has nothing to do with the seashore.
• Because the female rarely leaves her web, one patch of silk on a garage wall may be occupied continuously for two years or more, growing as she lays fresh layers over the old.

In summary, the grey house spider is a harmless, hard-working neighbour: a grey, web-bound Australian that has quietly colonised walls on four continents and pays its rent in moths. Learn the lacy sheet with a funnel at one corner and you will recognise it anywhere it turns up.