The black house spider (Badumna insignis) is native to Australia and is not established in California. If you’ve spotted a dark spider in or around your California home, you’re almost certainly looking at a different species. Several common California spiders share a similar dark, rounded appearance, and knowing which one you’re dealing with matters because their bite risks vary significantly.
What the Black House Spider Actually Is
The true black house spider is a robust, dark spider found throughout Australia and parts of New Zealand. Females grow up to 18 mm in body length with a 30 mm leg span, while males are smaller at around 10 mm. Both sexes have dark brown to black legs and carapace, with a charcoal grey abdomen covered in fine, velvety hair. The abdomen sometimes shows a faint pattern of lighter markings on top.
These spiders build distinctive lacy sheet webs with funnel-shaped entrances leading to a hidden retreat. They favor rough surfaces like bark, brick, window frames, and wall crevices, which is why they’re sometimes called “window spiders” in Australia. Their silk is unusual: instead of being sticky, it’s made from many ultra-fine combed strands that snag insect legs like Velcro. None of these webs are turning up in California, though. The species hasn’t crossed the Pacific in any documented way.
Dark Spiders You’ll Actually Find in California
California has several species that look dark, build messy webs near homes, and get lumped together under “black house spider” in casual conversation. Here are the most likely candidates.
False Black Widow (Steatoda grossa)
This is probably the spider you found. The false black widow is a European import that has become extremely common in Pacific Coast homes from San Diego to British Columbia. It’s chocolate brown with a rounded abdomen, about 10 mm in body length, and never has red markings on its belly. It builds tangled, messy cobwebs in corners, garages, and window frames. Its bite can cause mild pain and localized swelling but is not medically dangerous.
Noble False Widow (Steatoda nobilis)
Discovered in Southern California in 2011, this is another European species that’s still spreading. Mature females reach about 14 mm in body length, making them noticeably larger than the common false black widow. They’re dark brown with a bulbous abdomen and sometimes show faint cream-colored markings. Their bite is more painful than Steatoda grossa but still not considered a serious medical concern for most people.
Western Black Widow (Latrodectus hesperus)
This is the one worth being cautious about. The western black widow is native to California, widespread throughout the state, and poses the greatest spider bite risk in the western United States. Mature females are jet black with the characteristic red hourglass marking on the underside of the abdomen. They build irregular, strong webs close to the ground in sheltered spots: under patio furniture, in meter boxes, woodpiles, and garage clutter. If the spider you found is glossy black (not fuzzy or matte) and has any hint of red underneath, treat it as a black widow.
Brown Widow (Latrodectus geometricus)
The brown widow became established in southern California in the early 2000s and has spread rapidly. It’s tan to dark brown with an orange or yellowish hourglass marking rather than the bright red of the black widow. Its egg sacs are distinctive: spiky and round, like tiny sea urchins. While venomous, the brown widow tends to inject less venom per bite than the black widow, and serious reactions are uncommon.
How to Tell Them Apart
Color alone won’t reliably identify your spider, since several of these species range from brown to nearly black depending on age and light. Focus on a few key details instead. A glossy, hairless abdomen with red markings points to a widow. A matte brown or chocolate body with no red at all is likely a false black widow. Check the web, too: widows build strong, three-dimensional tangles with thick silk near ground level, while false widows spin messier, flimsier cobwebs higher up on walls and ceilings.
Body shape helps as well. All of the species listed above have round, bulbous abdomens, but widows tend to look smoother and shinier. If the spider appears fuzzy or velvety, it’s not a widow. Size is a rough guide: a body length under 10 mm with no red or orange markings is most likely a harmless false black widow.
What to Do if You’re Bitten
For bites from false black widows and other non-dangerous species, basic first aid is all you need. Clean the bite with mild soap and water, apply an over-the-counter antibiotic ointment, and hold a cool, damp cloth over it for about 15 minutes each hour to reduce pain and swelling. Elevate the area if possible, and take an over-the-counter pain reliever or antihistamine as needed.
Seek emergency medical care if you think the bite came from a black widow, if you develop severe pain or stomach cramping, if the bite area keeps growing or develops spreading red or purple streaks, or if you have any trouble breathing or swallowing. If you’re unsure which spider bit you, err on the side of getting medical attention.
Keeping Spiders Out of Your Home
Regular, thorough cleaning is the single most effective spider control method. Vacuuming or sweeping removes spiders, webs, and egg sacs, and destroying those egg sacs is especially important since each one can contain hundreds of young spiders. Focus on quiet, undisturbed spots like closets, garages, attics, and storage areas. Reducing clutter in these zones makes them far less appealing.
Outside, move firewood, stacked materials, and debris away from your home’s foundation. Trim back shrubs, vines, and tree branches that touch the house, since these give spiders both a hiding spot and a direct bridge indoors. Install tight-fitting window screens and door sweeps to close off entry points.
Lighting matters more than you might expect. Standard outdoor bulbs attract night-flying insects, which in turn attract the spiders that eat them. Switching to yellow or sodium vapor bulbs at exterior doors reduces that food source. If you want to find out where spiders are concentrated, place sticky glue traps flush against the base of walls and in room corners. They’ll reveal hotspots you might not notice during a visual inspection.