Brown widow spiders outnumbered western black widows about 20 to 1 in timed searches around urban Southern California homes, in Vetter et al. 2012, Journal of Medical Entomology 49:947-951 (Los Angeles Basin collections; the paper also notes brown widows had spread through the San Diego metropolitan area by then). If you’ve spotted a shiny black spider or a mottled tan one under patio furniture, UC IPM’s egg-sac test is the field mark that does not need a lab. Here’s how to tell them apart, which bite actually needs a doctor, and when a licensed company should look.
How to tell a brown widow from a black widow
These two spiders are cousins, and people mix them up constantly. A few details settle it fast.
- Body color: Black widows are shiny, jet black. Brown widows run tan to dark brown with a mottled, marbled pattern down the back.
- Hourglass marking: Both have an hourglass shape on the underside of the abdomen. On a black widow, it’s bright red or orange. On a brown widow, it’s a duller orange or yellow, and sometimes hard to see at all.
- Size: UC IPM: a mature female western black widow is about 1/2 inch (13 mm) in body length, not counting legs. A mature female brown widow is smaller, about 3/8 inch (10 mm) in body length.
- Egg sacs: This is the giveaway when the spider itself is hiding. UC IPM: black widow egg sacs are yellowish, teardrop-shaped, with a tough covering. Brown widow egg sacs have silk protuberances all over the surface, like a large pollen grain.
- Behavior: Brown widows are skittish. Disturb one and it’s more likely to curl up and drop than stand its ground, which is part of why bites are so rare.
Why brown widows took over San Diego
Brown widows aren’t native to California. UC IPM: they became established in Southern California in the first decade of the 21st century. Vetter et al. 2012, Journal of Medical Entomology 49:947-951, used timed searches in the urban Los Angeles Basin. Around homes, brown widows were collected at about 8.59 per collector-hour versus 0.42 western black widows, about twenty times lower for black widows. That is not a San Diego yard census. The same paper records that brown widows had spread through the San Diego metropolitan area.
UC IPM cites that 2012 study for brown widows outnumbering black widows in urban areas around homes, parks, and playground equipment, and not in chaparral. Because brown widow bites are milder, UC entomologists note that a shift toward brown widows might lower overall serious-bite risk compared with previous decades.
Where each one hides around your property
Black widows still stick to the classic hideouts: garages, woodpiles, sheds, and other dark, undisturbed corners close to the ground. Brown widows are bolder. Check these spots first:
- Undersides of patio furniture and cushions
- Chain-link fences and mailboxes
- Garbage cans, buckets, and recycling bins left outside
- Eaves, window wells, and outdoor light fixtures
- Playground and play structure equipment
Because brown widows tolerate more exposed, higher-traffic areas, they’re the spider your kids or pets are more likely to run into during normal yard use.
Which bite is actually dangerous
Both spiders carry neurotoxic venom, but the two bites aren’t close in severity.
A black widow bite is a real medical event. UC IPM: the bite itself is painless or may feel like a pinprick. Within an hour, other symptoms may start, including rigid stomach muscles that some clinicians have mistaken for appendicitis. Seek medical attention. Do not treat this page as a complete symptom list.
A brown widow bite is a different story. UC IPM: the bite of the brown widow is much milder than that of the western black widow. Combine that with the brown widow’s habit of playing dead and dropping rather than biting when disturbed, and bites to people stay uncommon.
If you’re bitten by either spider and you’re not sure which one it was, treat it like a black widow bite until a doctor tells you otherwise. Try to safely capture the spider for identification if you can do it without risking another bite.
What to do if you find one
A single spider in an isolated spot is usually a DIY job. Vacuum it up, egg sac included, using a hose attachment so your hands stay away from the web. Wear gloves regardless of which species you think it is.
A widow problem becomes a professional job when you’re finding multiple spiders across the property, egg sacs keep reappearing after you clear them, or the spiders are in an area kids and pets use regularly, like a play structure or a patio. Our guide to DIY vs. professional pest control walks through that decision in more detail. If you’ve already confirmed black widows specifically, our black widow control guide covers removal step by step. For a broader look at what else might be sharing your yard, see our guide to common spiders in San Diego, and if the spider you found doesn’t match either widow, check whether it’s actually a brown recluse look-alike, a spider that’s rarer here than most people think.
A licensed company may vacuum or treat active spiders and egg sacs, then discuss residual work around foundations and harborage. Ask what is in the written scope. That is a spider control match request anywhere in our San Diego County service area. Pest Pros San Diego does not send a technician.
Frequently asked questions
Are there black widows in San Diego?
Yes. Black widows live throughout California, including San Diego County. They are often outnumbered around urban homes. Vetter et al. 2012, Journal of Medical Entomology 49:947-951, found brown widows about 20 times more often than western black widows in timed searches around urban Southern California homes in the Los Angeles Basin. A shiny jet-black widow with a bright red hourglass is still a real find here. UC IPM: both favor cluttered outdoor harborage such as woodpiles; brown widows also use more exposed spots such as chain-link fences and plastic patio furniture.
Are brown widow spiders dangerous to pets?
UC IPM’s widow notes describe human bite observations, not dogs or cats. We do not have a sourced pet-bite description. If a pet is bitten, call a veterinarian. Do not use this page as veterinary advice.
Do brown widows bite as often as black widows?
No. Brown widows are far more numerous around San Diego homes, but they’re also more likely to retreat or play dead than to bite when disturbed. Bites from either species are uncommon, and most happen when a spider gets trapped against skin, like inside a shoe or a glove.
How do I get rid of brown widow egg sacs?
Vacuum them up along with the spider using a hose attachment, then seal the vacuum bag or empty the canister into a sealed bag outside. UC IPM: brown widows produce about 130 eggs per sac, so leaving a sac behind undoes the rest of the cleanup.
Are brown widows an invasive species in California?
Yes. Brown widows aren’t native to California. UC IPM: they were first documented as established in Southern California in the early 2000s. Vetter et al. 2012 records spread through the Los Angeles and San Diego metropolitan areas.
Can brown widows and black widows share the same yard?
Yes, and in San Diego it’s common. They favor slightly different spots, black widows in darker, more enclosed areas like woodpiles and garages, brown widows in more exposed spots like patio furniture and fences, so a single property can easily host both.
UC IPM: black widows are common in garages; brown widows are not. Outside around the home, both can be common. Finding one widow in harborage does not mean the property is overrun. For a population past one corner, request a match. Pest Pros San Diego is not the company that treats the yard.
If you’re finding widow spiders around your home and want a licensed look, call (858) 400-6561 to get matched with a licensed local company.