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How to identify it
- Mature females are about 3/8 inch (10 mm) in body length and mottled tan, brown and gray, though color ranges from almost white to almost black; dark ones are a flat black rather than the shiny black of a mature black widow.[1]
- The egg sac is covered in pointed silk bumps, like a large pollen grain, and confirms brown widows even when no spider is seen.[1][4]
- Males are much smaller, about 3/16 inch (4 to 5 mm), and easy to overlook.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Immature black widow | Very similar. Brown widows usually have a tan background and large, squarish black spots on the side stripes, while young western black widows are more olive gray with small, elliptical spots; the spiky egg sac is the surest way to tell.[1] |
Where it lives
Found worldwide in subtropical areas and now reported from nearly every country in the Americas. In the U.S. it was long known only from Florida; since the 2000s it has been found in Texas, Louisiana, Mississippi (as far north as a county bordering Tennessee), Georgia and up the Atlantic coast into South Carolina, and in Southern California, where as of 2016 it was established from Santa Barbara to the San Bernardino area and south to Mexico.[1][2][5][3]
Biology and life cycle
Females lay about 130 eggs per sac and can make 20 or more sacs in a lifetime, sometimes several within a short time.[1]
When disturbed, brown widows usually pull in their legs, drop from the web and play dead.[1]
Females guard their egg sacs, and in experiments the spikes helped: wasps that parasitize widow eggs laid more eggs on the side of a sac where spikes had been removed, and females exposed to the wasps made later sacs with denser spikes.[4]
Very dense brown widow populations in towns had parasitism rates of only 0 to 5 percent, and researchers think fewer predators and parasites in built-up areas help it spread.[6][4]
Damage and signs
- Around homes it hides where fingers go: under the lips of plastic patio furniture and potted plants, in the recessed handles of plastic trash bins and under playground equipment.[1][3]
- In urban Los Angeles, brown widows greatly outnumbered native western black widows around homes, in parks and in plant nurseries, but were rare or absent in garages, crops and natural areas, and neither widow was found in the living space of homes.[3][1]
Health risk
Brown widow venom carries alpha-latrotoxin like other widows and its bites can cause the same kind of symptoms, but bites are less toxic than western black widow bites and documented cases are rare. A 2008 case report of a previously healthy patient who needed hospital care shows a bite can still be serious.[7][3][8]
Control
Prevention
Wear gloves when moving stacked materials or cleaning garages and sheds, and shake out gloves, clothing and shoes stored outdoors before use.[10][9]
Keep them out
Seal cracks in the foundation, keep screens and doors tight, and point outdoor lights away from doors and windows so they attract fewer insects.[9][1]
Sanitation
Remove clutter, woodpiles, leaf litter and heavy vegetation next to the foundation, and vacuum or sweep webs and spiders regularly; vacuumed spiders usually don't survive.[9][1]
Traps and physical control
Check and wipe out the undersides of patio furniture, play equipment and other outdoor objects with sheltered lips, and remove the spiky egg sacs. Widows are active at night, so a flashlight search after dark finds them.[1][3]
Pesticides
Insecticides don't give long-term spider control and generally shouldn't be used against spiders outdoors; spraying is only temporary without housekeeping.[9][1]
If someone is bitten
NIOSH first aid for a spider bite: stay calm, wash the bite with soap and water, apply a cold, damp cloth or wrapped ice, raise the area if possible, don't try to remove venom, and seek medical care.[10]
For widow bites, MedlinePlus advises getting medical help and calling Poison Control (1-800-222-1222). Keep the area still, remove rings and tight clothing, and bring the spider in a secure container if you can. Children, pregnant women and older people may be given widow antivenom.[11]
A doctors' review notes widow antivenom isn't widely available in the U.S. and is considered for severe cases; a patient with a confirmed brown widow bite improved quickly after antivenom.[12][7]
Why it spreads so well
The brown widow is one of the most successful invasive spiders: in the Americas it is found mainly around houses but also in farm areas.[5][4]
Its egg sacs suffer little from parasitic wasps in towns, and its guarding behavior and spiky sacs fend them off, which may give it an edge over native widows.[6][4]
In Southern California the brown widow appears to be displacing the more toxic western black widow, so researchers suggest the overall risk of widow bites there may actually be lower than before it arrived.[3][1]
Where sources disagree
Bite severity: a Southern California study found brown widow bites less toxic than black widow bites, but a 2008 case report of a previously healthy patient hospitalized with severe pain, cramps, vomiting and muscle twitching called for rethinking the idea that brown widow bites are minor.[3][8]
Common questions
- Is the brown widow more dangerous than a black widow?
- Usually not. Its bite is less toxic than a western black widow's, though its venom contains the same main toxin and at least one bite has needed hospital care.[3][7][8]
- Will I find brown widows inside my house?
- Rarely. They live outside around homes, parks and playgrounds; a Southern California survey found none in the living space of homes, and UC IPM says they are uncommon in garages.[3][1]
- How can I tell it's a brown widow and not a black widow?
- Look for the egg sac: brown widow sacs are covered in pointed silk bumps, while the female's tan, mottled body is easy to confuse with a young black widow.[1][4]
Sources
- University of California Statewide IPM Program, “Pest Notes: Widow Spiders and Their Relatives, Publication 74149 (revised March 2017).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnblackwidow.pdf (accessed 2026-11-11)
- Journal of Medical Entomology, via PubMed, “Brown, Necaise and Goddard (2008), Additions to the known U.S. distribution of Latrodectus geometricus (Araneae: Theridiidae).” pubmed.ncbi.nlm.nih.gov/18826042/ (accessed 2026-11-11)
- Journal of Medical Entomology, via PubMed, “Vetter, Vincent, Danielsen and others (2012), The prevalence of brown widow and black widow spiders (Araneae: Theridiidae) in urban southern California.” pubmed.ncbi.nlm.nih.gov/22897057/ (accessed 2026-11-11)
- Proceedings of the Royal Society B, via PubMed, “Arabesky, Johnson, Rozenberg, Lubin, Segoli and Mowery (2025), Maternal care thwarts parasitoids in the invasive brown widow spider (Latrodectus geometricus).” pubmed.ncbi.nlm.nih.gov/40328306/ (accessed 2026-11-11)
- Environmental Entomology, via PubMed, “Taucare-Rios, Bizama and Bustamante (2016), Using global and regional species distribution models to infer the invasive stage of Latrodectus geometricus in the Americas.” pubmed.ncbi.nlm.nih.gov/28028084/ (accessed 2026-11-11)
- Oecologia, via PubMed, “Mowery, Arabesky, Rozenberg, Lubin and Segoli (2023), Invasive brown widow spiders avoid parasitism despite high densities.” pubmed.ncbi.nlm.nih.gov/37160461/ (accessed 2026-11-11)
- Toxicon, via PubMed, “Keyler, Ahmad, Rodriguez and De Silva (2020), Latrodectus geometricus envenoming: rapid resolution of symptoms following F(ab')2 antivenom therapy.” pubmed.ncbi.nlm.nih.gov/33068558/ (accessed 2026-11-11)
- Southern Medical Journal, via PubMed, “Goddard, Upshaw, Held and Johnnson (2008), Severe reaction from envenomation by the brown widow spider, Latrodectus geometricus.” pubmed.ncbi.nlm.nih.gov/19005454/ (accessed 2026-11-11)
- University of California Statewide IPM Program, “Pest Notes: Spiders, Publication 7442.” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnspiders.pdf (accessed 2026-11-11)
- Centers for Disease Control and Prevention, NIOSH, “Venomous Spiders at Work (Sept. 28, 2026).” www.cdc.gov/niosh/outdoor-workers/about/venomous-spiders.html (accessed 2026-11-11)
- MedlinePlus, U.S. National Library of Medicine, “Black widow spider (Medical Encyclopedia).” medlineplus.gov/ency/article/002858.htm (accessed 2026-11-11)
- American Family Physician, via PubMed, “Herness, Snyder and Newman (2022), Arthropod bites and stings.” pubmed.ncbi.nlm.nih.gov/35977137/ (accessed 2026-11-11)
- iNaturalist, “Latrodectus geometricus taxon page (order and family).” www.inaturalist.org/taxa/47383 (accessed 2026-10-06)