Black house spiders are not considered dangerous. Their bite can be painful and cause some swelling, but they are timid and rarely bite at all. The Australian Museum also makes clear that they are not related to funnel-web spiders, even though their webs have a funnel-shaped entrance. The bigger issue in most Shire homes is how many settle around the windows.
How do you identify a black house spider?
The black house spider, *Badumna insignis*, is a dark, solid-looking spider. The Australian Museum describes a dark brown to black body and legs, grey hairs on the front section, and a charcoal grey abdomen with white markings that are sometimes hard to see.
The web is the easiest clue. It is a lacy, untidy sheet of silk spread around one or more funnel-like entrances that lead back into a crack or gap. The silk is not sticky. It is made of very fine combed strands that snag the spiny legs of insects. Older webs turn grey and woolly as the spider keeps adding layers. That is why they are also called window spiders: window frames, wall crevices, brickwork and rough tree bark are where these webs build up.
How is it different from a funnel-web spider?
The funnel shape in the web causes most of the confusion. The Australian Museum notes that black house spiders are not related to Australian funnel-webs and are not similar in appearance, size or life history.
A true funnel-web usually lives in a burrow in the ground. One exception is the southern tree funnel-web, which burrows into crevices in tree trunks, much like the places black house spiders choose. The museum points to the silk to tell them apart. A tree funnel-web disguises its crescent-shaped entrances with bits of bark worked into the silk. Black house spider silk is left exposed and lacy.
So a grey, woolly web in the corner of a window frame is almost certainly a black house spider. A spider wandering across the floor or the pool area at night, or coming out of a hole in the garden bed, needs more care. If you cannot tell which spider you are dealing with, keep clear of it and leave the identification to a technician.
What does a black house spider bite do?
The Australian Museum describes the bite as painful with local swelling. Nausea, vomiting, sweating and giddiness are occasionally recorded, and in a few cases skin lesions developed after several bites.
A prospective study by Geoffrey Isbister and Michael Gray, published in the Internal Medicine Journal in 2004 and listed on PubMed, followed 25 people with confirmed bites from *Badumna* spiders. Every person had pain, and it was severe in seven cases, but the median time it lasted was five minutes. Redness appeared in 68% of cases, puncture marks in 24% and swelling in 12%. None of the 25 people developed a necrotic ulcer, and the authors concluded that black house spiders are unlikely to cause one. Most bites happened in daylight, and 92% between October and March.
If symptoms persist, or you are not sure which spider bit you, see a doctor.
Why do black house spiders settle around the house?
Because the house brings their food to them. The Australian Museum notes that around homes they feed on moths, beetles and termites drawn to the light of windows and lamps at night. Museums Victoria notes that webs built near porch and outdoor lights get a steady supply of insects.
The female almost never leaves her web unless she is forced to, and she keeps several white egg sacs inside the retreat until they hatch. The spiders mature over summer and live for about two years.
Jannali is mostly homes and bushland reserve. A Jannali house backing onto bush, with grey woolly webs in every window frame on the back wall and around the outdoor light, is a good case for spider control in Jannali that treats the frames, eaves and the light fittings where the insects gather.
Bonnet Bay sits on the Woronora River, with sandstone gullies and parks covering almost a quarter of the suburb. A Bonnet Bay home with sandstone retaining walls and rough-barked trees close to the house gives black house spiders plenty of crevices to build in, so spider control in Bonnet Bay should take in the walls and trees near the house as well as the windows.
Why do they matter if they are not dangerous?
Museums Victoria describes black house spiders as one of the white-tailed spider's preferred foods, and the Australian Museum lists the white-tailed spider among their enemies. A house with webs in every window frame is likely to see white-tailed spiders hunting through the rooms at night.
One untidy window corner is easy to live with. When webs cover the eaves, the pergola and every frame along one side of the house, the problem is the number of spiders and the insects feeding them.
A Cronulla apartment near the beach where black house spider webs keep filling the balcony door frame and the light above it needs fast spider control in Cronulla before white-tailed spiders follow them inside.
A family in Barden Ridge who has found a white-tailed spider in the bedroom, and grey webs in the window frames along the same wall, should book spider control in Barden Ridge and ask the technician to check where the black house spiders are living, since that is where the hunters are finding food.
Before you book
Note these details so the technician can plan the visit:
- which windows, walls or light fittings have the most webs
- whether the webs are grey and woolly, or whether you have seen a spider on the ground or near a hole in the garden
- whether anyone has been bitten, and whether you have seen white-tailed spiders inside
- whether trees, sandstone walls or bush sit close to the house
Send those details to our team for pest control for homes across the Sutherland Shire: call Sutherland Shire Pest Control Pro on 02 8360 3033 or email [email protected].