Black Widow vs False Widow: How to Tell Them Apart
A black widow is shiny jet black with a red hourglass under its abdomen; a false widow is a duller purplish to chocolate brown and never has red on its belly. Both are round-bodied cobweb spiders of the same family, which is why they get confused. The false black widow, Steatoda grossa, has mild venom and causes pain rather than serious illness. True black widows are one of only two spider groups the CDC lists as venomous in the United States, although US poison centres recorded no deaths among nearly 10,000 symptomatic exposures from 2000 to 2008.
Most guides to this question are written for Britain, which has no black widows. In the United States you can meet three black widow species, the brown widow and several false widows, sometimes in one garage.
Black widow vs false widow at a glance
| Black widows (southern, northern, western) | Brown widow | False black widow | |
|---|---|---|---|
| Genus | Latrodectus | Latrodectus geometricus | Steatoda grossa |
| Adult female colour | Shiny jet black; well-fed females can look plum or brownish | Mottled tan, brown and grey; dark ones are flat black, not glossy | Purplish brown to black, often with faint pale markings |
| Underside | Red hourglass, complete in the southern species, split in the northern, variable in the western | Orange hourglass, bottom half larger with rough edges; dark bands on the legs | No red at all |
| Adult female body length | 8 to 13 mm, about 1/3 to 1/2 inch | About 10 mm, 3/8 inch | 6 to 10.5 mm, about 1/4 to 3/8 inch |
| Egg sac | Tough, smooth, with crisp edges | Covered in silk spikes, like a large pollen grain | Fluffy, like a cotton ball with no clear edge |
| Indoors? | Rarely in living spaces; common in garages, sheds and wood piles | Almost never in homes; patio furniture, fences, plant pots | Thrives indoors: cupboards, bathrooms, under appliances |
| Bite | Neurotoxic; medical attention advised | Much milder than a black widow | Mild; local pain, sometimes nausea or headache |
If you only check one thing, check the underside. UC IPM states that the false black widow “never has red coloration”, while a true widow carries a red or orange mark there.
How to tell a black widow from a false widow in five checks
Work in this order. It also works for black widow vs false widow pictures: one photo from below, abdomen in focus, beats five from above.
- Look underneath. A red or orange hourglass, or two red triangles, means a widow. No red anywhere on the belly points to a false widow or another cobweb spider.
- Judge the shine. Adult female black widows are glossy jet black. False widows are purplish brown, and brown widows that happen to be dark are a flat black.
- Read the back. A false widow often shows faint pale yellow or greyish marks and a light crescent at the front of the abdomen, though these fade in many adult females. Northern black widows carry a row of red spots down the middle of the back.
- Find the egg sac. Widow sacs have crisp margins and are hard to tear; brown widow sacs are spiky; false widow sacs look like loose cotton wool.
- Note where it is. A round dark spider living in a kitchen cupboard or bathroom in Washington or coastal California is far more likely to be a false widow, which UC IPM says thrives indoors, than a black widow, which usually cannot find enough prey inside homes.
Why juveniles and males cause the arguments
Much online debate involves spiders that are not adult females. UC IPM describes young western black widows as tan or olive grey with a white stripe down the back, and adult males keep that pattern. The hourglass starts as a whitish shield and turns orange red with each moult, so a striped tan spider with an orange mark underneath is usually a young widow, not a harmless species. The western black widow’s hourglass can also be split, reduced to red flecks or, rarely, absent. False widow spiderlings, by contrast, are dark like their mother from hatching.
Are false widows still black widows?
No. False widows belong to the genus Steatoda, not Latrodectus. They share the cobweb spider family, Theridiidae, with true widows, hence the round abdomen and the tangled web. Penn State Extension counts eight Steatoda species in the United States.
- Steatoda grossa, the false black widow or cupboard spider. Found in Atlantic, Gulf and Pacific coastal states; UC IPM calls it extremely common in Pacific Coast homes from San Diego to British Columbia.
- Steatoda borealis. Slightly smaller and more common in the northern states.
- Steatoda nobilis, the noble false widow. Found in Southern California in 2011 and now widespread on the California coast. Females reach 14 mm, about 5/8 inch, with a tan pattern like a house with two windows.
Penn State notes that S. grossa is reported to prey on other spiders, including black widows, and that females may live up to six years; our guide to how long spiders live compares other species.
Brown widow vs black widow, and false widow vs brown widow
The brown widow is a true widow and the one most often confused with both others. UC IPM records it only in Florida for decades, then, in the 2000s, from Texas along the Gulf Coast into South Carolina and in great numbers in Southern California. A 2006 to 2008 survey found it in Georgia, Texas, Louisiana and Mississippi. An adult brown widow looks very like a young western black widow, so UC IPM publishes a key, extended here with a false widow column.
| Feature | Brown widow | Young western black widow | False black widow |
|---|---|---|---|
| Background colour | Tan, mottled with brown and grey | Olive grey | Purplish brown to black |
| Black spots on side stripes | Large, squarish | Small, elliptical | Markings faint or absent |
| Hourglass | Bottom half larger, rough margins | Top half larger, crisp straight margins | None |
| White marks at front of abdomen | Not continuous | Continuous | Pale crescent, often faded |
| Egg sac | Spiky, about 130 eggs | Mother’s sac smooth teardrop, about 300 eggs | Cottony, 200 or more eggs |
| Favourite spot | Undersides of plastic patio furniture, fences, pot rims | Holes, cracks and clutter near the ground, garages | Indoors, low and dark |
UC IPM says the brown widow’s spiky sac can confirm the species even when no spider is seen. In a 2012 Los Angeles Basin survey brown widows greatly outnumbered western black widows around homes, and neither was found in living spaces.
Where each spider turns up: our state analysis
We divided each state’s iNaturalist research-grade records of each spider by its total observations of anything, so busy states do not dominate. These are photographed sightings, mostly outdoors, not infestation rates.
Western black widows dominate the dry interior West: Utah has 25.99 records per 10,000 observations and New Mexico 21.57. The southern black widow peaks in Oklahoma at 13.71, then Arkansas and Mississippi. Texas is the meeting point, with 2,666 southern black widow records, 1,971 western black widow records and 1,392 brown widow records; our guide to common house bugs in Texas covers what else turns up there.
Brown widow records follow its documented arrival route. California has the highest rate at 7.07, then South Carolina, Georgia and Florida, with Louisiana, Mississippi and Alabama close behind. Away from the South and California the rates fall close to zero.
The false black widow is the Pacific Coast spider of the four, with a second cluster in the Southeast. Washington leads at 4.81, ahead of California at 3.81, then North Carolina and Georgia, and Washington has almost no brown widow records at all. Many false widow photos are identified only to genus, so these rates likely understate false widows overall.
When you are most likely to see each one
The widows and the false widow keep opposite calendars. Southern and western black widows and the brown widow climb through summer to a peak in September and October, at close to twice their usual share of all records. That matches US poison centre data, where black widow exposures peaked in September and bottomed out in January and February.
The false black widow does the reverse, peaking in November at 198 and staying high through January, with its lowest share in spring. It lives indoors year round, so the winter rise mostly reflects people noticing it when little else is about. Still, a dark round spider indoors in December is, on the odds, a false widow.
Black widow vs false widow bite
| Black widow | Brown widow | False widow | |
|---|---|---|---|
| Venom | Neurotoxin (alpha-latrotoxin) | At least as potent drop for drop, but far less injected | Mild; in laboratory tests it acts in a similar way to widow venom |
| Typical effects | Spreading pain, muscle cramps and rigidity, sweating | Pain and burning at the bite site | Local pain like a yellowjacket sting, minor swelling |
| Published case data | 9,872 symptomatic US exposures 2000 to 2008, no deaths | 15 verified bites in Africa, none with typical widow symptoms | 23 verified bites in Australia; severe pain in 26% |
| Who bites | Almost always the adult female | Rarely bites; drops and plays dead | Mostly indoors, often while dressing |
How venomous is a false black widow?
Mildly. UC IPM likens the bite to a yellowjacket sting: burning pain, then minor swelling. An Australian study of 23 bites by expertly identified Steatoda found pain in every case, severe in six, lasting a median six hours, with nausea, headache or malaise in 30 per cent. Penn State reports symptoms lasting one to 60 hours. Because they live in homes, UC IPM says false widows cause more bite incidents than true widows; 78 per cent of the Australian bites happened indoors.
What’s worse, false widow or black widow?
A black widow bite is clearly worse. Its venom acts where nerve meets muscle, and UC IPM lists rigid stomach muscles, sweating and spreading pain. Even so, US poison centre data are reassuring. Of 9,872 symptomatic exposures from 2000 to 2008, 65 per cent had minor effects, 33.5 per cent moderate, 1.4 per cent major, and there were no deaths. A later review of 15,299 exposures from 2012 to 2022 found 10.0 per cent were admitted to hospital.
For a suspected widow bite UC IPM advises seeking medical attention immediately; treatment is for a doctor or poison centre. Our bite identification guide explains why marks alone mislead.
Should I kill a false widow spider?
You do not need to. A false widow is not a medical risk in the way a black widow is, and it eats insects and even true widows. If you want it gone, UC IPM’s widow methods work here too:
- Vacuum it. Spiders’ soft bodies usually do not survive it, UC IPM says. Take the web and egg sac too.
- Or move it. Jar and paper, then release outdoors. Never handle a round-bodied spider bare-handed until a widow is ruled out.
- Remove the habitat. Clear low clutter and seal gaps around doors and foundations, as Montana State University Extension advises.
- Skip the fogger. Montana State says bug bombs do not work on house spiders, and UC IPM says insecticides give no long-term control. Use any product exactly as its label says.
See how to get rid of spiders in the house for sealing and the repellent evidence.
When to call a professional
A false widow problem is almost always a DIY job. True widows are different when numerous around small children, in a shed you use daily, or in play equipment; UC IPM notes that in good habitat, female western black widows can be found every few feet. Gloves, sealing and decluttering come first, but a licensed professional who inspects before treating can find harbourage you are missing. Be wary of fear-driven programmes for what turns out to be a false widow; as with the hobo spider, reputation can outrun evidence. For other species, see our spider identification guide.
Frequently asked questions
What is the deadliest house spider?
In the United States, the CDC names only two groups of venomous spiders: black widows and the brown recluse. Black widows rarely live in living spaces, where UC IPM says they usually cannot find enough prey. Even for black widows, US poison centres recorded no deaths among 9,872 symptomatic exposures between 2000 and 2008. The false black widow is the round dark spider most often found indoors, and its bite is mild.
Are false widow spiders dangerous?
Not in the way black widows are. Montana State University Extension calls them harmless to humans, and UC IPM compares a bite to a yellowjacket sting. In an Australian study of 23 verified bites, pain was universal and severe in about a quarter, and most patients received no treatment. Anyone with spreading pain or feeling unwell after a bite should see a doctor.
Does a false widow have a red hourglass?
No. UC IPM states that the false black widow never has red colouring on its underside, and Penn State says it lacks the red hourglass. Its back may show faint pale marks, often faded in adult females. Any red or orange mark on the belly of a round, glossy spider means you should treat it as a true widow.
How big is a false widow compared with a black widow?
Slightly smaller. Penn State gives adult female false black widows as 6 to 10.5 mm in body length, about a quarter to three eighths of an inch. Adult female black widows run from about 8 to 13 mm depending on species and source, with the western black widow around 13 mm, half an inch. The noble false widow is the exception, reaching about 14 mm.
Can a false widow kill a black widow?
Reportedly, yes. Penn State Extension notes that Steatoda grossa is reported to capture and prey on other spiders, including true black widows, and the two can share sheltered spots around buildings. That does not make false widows a control method for widows, but it is one more reason a confirmed false widow in a shed or garage can usually be left alone rather than sprayed.
Sources
- University of California Statewide IPM Program, Pest Notes: Widow Spiders and Their Relatives, UC ANR Publication 74149 (R. S. Vetter), 2017.
- Penn State Extension, False Black Widow Spider.
- Montana State University Extension IPM, Cobweb Weavers and False Widows (Steatoda spp.), fact sheet, November 2022.
- University of Florida IFAS, Featured Creatures EENY-560, Southern Black Widow, Latrodectus mactans (Eiden and Kaufman), 2013.
- Connecticut Agricultural Experiment Station, Northern Black Widow, Southern Black Widow fact sheet (R. Hiskes).
- Centers for Disease Control and Prevention, NIOSH, Venomous Spiders.
- Clemson Cooperative Extension, Home and Garden Information Center, Widow Spiders.
- Graudins, Gunja, Broady and Nicholson, Clinical and in vitro evidence for the efficacy of Australian red-back spider antivenom in the treatment of envenomation by a cupboard spider (Steatoda grossa), Toxicon 40:767 to 775, 2002.
- Natural History Museum, London, Identifying false widow spiders.
- Isbister and Gray, Effects of envenoming by comb-footed spiders of the genera Steatoda and Achaearanea in Australia, Journal of Toxicology: Clinical Toxicology 41:809 to 819, 2003.
- Monte, Bucher-Bartelson and Heard, A US perspective of symptomatic Latrodectus spp. envenomation and treatment: a National Poison Data System review, Annals of Pharmacotherapy 45:1491 to 1498, 2011.
- Kerns, Scheffel, Farah and Holstege, Black widow spider exposures: a retrospective review of the National Poison Data System 2012 to 2022, Wilderness and Environmental Medicine 36:154 to 158, 2025.
- Vetter and others, The prevalence of brown widow and black widow spiders in urban southern California, Journal of Medical Entomology 49:947 to 951, 2012.
- Brown, Necaise and Goddard, Additions to the known U.S. distribution of Latrodectus geometricus, Journal of Medical Entomology 45:959 to 962, 2008.
- The Pest Control Brief analysis of iNaturalist research-grade records, pulled October 2026.
