Southern black widow vs False black widow
These two are easy to mix up. Here's how to tell a southern black widow from a false black widow, and whether either one bites or stings.
Southern black widow
Latrodectus mactans
False black widow
Steatoda grossa
≠The key differences
Generally rounder and duller brown or purple-black; lack the clear red hourglass and are less likely to cause severe envenomation, causing only mild bite symptoms.
⚖︎Side by side
| Southern black widow | False black widow | |
|---|---|---|
| To humans | Venomous bite | Venomous bite |
| Size | Females 8-13 mm body length; males 3-6 mm body length | Females 6-10 mm body length; males 4-8 mm |
| Colours | Black, Red, Brown, White | Dark brown, Purplish brown, Pale cream (faint markings) |
| Family | Theridiidae | Theridiidae |
| Habitat | Sheltered, undisturbed sites near the ground: woodpiles, boxes, garages, basements, crawlspaces, hollow stumps, under eaves and inside cluttered storage. | Human structures (houses, basements, garages), sheds, under eaves, rock crevices and debris piles |
| Range | Southeastern and south-central United States, west to Texas and Oklahoma and north to about the Ohio Valley and southern New England; most common in the southeast. Exact range and taxonomy can vary with local populations. | Originally from the Mediterranean and Macaronesia region; now nearly cosmopolitan, commonly found across North America, Europe and many other parts of the world |
| Active | Most active in warm months (spring to fall); nocturnal and most active at night when hunting in their webs. | Active year-round in heated buildings; outdoors most active spring through autumn and mainly nocturnal |
| Pest? | No | Yes |
🔍How to spot a southern black widow
- Shiny black, globular abdomen on females with a red hourglass marking on the ventral side.
- Females 8-13 mm body length; males much smaller and often brownish with dorsal markings.
- Tangled irregular cobwebs in sheltered, undisturbed areas near the ground or in buildings.
- Hourglass marking is usually on the underside of the abdomen; look at web location and body shape if marking is not visible.
🔍How to spot a false black widow
- Round, smooth, shiny abdomen; body length 4-10 mm depending on sex
- Uniform dark brown to purplish coloration; may show faint pale markings but lacks bright red hourglass
- Builds irregular, tangled cobwebs in sheltered corners, often near the ground or in undisturbed indoor areas
- Compare size and markings to distinguish from related species (see similar species)
?Frequently asked questions
What is the difference between a southern black widow and a false black widow?
Generally rounder and duller brown or purple-black; lack the clear red hourglass and are less likely to cause severe envenomation, causing only mild bite symptoms.
Is a southern black widow or a false black widow more dangerous?
Southern black widow: Venomous bite. False black widow: Venomous bite. Female bites inject neurotoxic venom (latrotoxin) that can cause local pain, muscle cramps, sweating, nausea, elevated blood pressure, and in severe cases respiratory difficulty. Bites are uncommon and usually occur when a spider is pressed against skin.
Identification from photos is never certain: don't handle insects you can't identify, and get medical advice for bites, stings or allergic reactions.