False black widow vs Northern black widow
These two are easy to mix up. Here's how to tell a false black widow from a northern black widow, and whether either one bites or stings.
False black widow
Steatoda grossa
Northern black widow
Latrodectus variolus
≠The key differences
False widows (Steatoda) are usually brown to purplish-black with paler markings and no red hourglass; their bites are generally far less severe.
⚖︎Side by side
| False black widow | Northern black widow | |
|---|---|---|
| To humans | Venomous bite | Venomous bite |
| Size | Females 6-10 mm body length; males 4-8 mm | Females about 8-13 mm body length; males about 3-6 mm |
| Colours | Dark brown, Purplish brown, Pale cream (faint markings) | Glossy black, Red (hourglass marking), Brown (male) |
| Family | Theridiidae | Theridiidae |
| Habitat | Human structures (houses, basements, garages), sheds, under eaves, rock crevices and debris piles | Undisturbed, sheltered locations near the ground: woodpiles, garages, basements, sheds, crawl spaces, hollow logs and under stones or debris. |
| Range | Originally from the Mediterranean and Macaronesia region; now nearly cosmopolitan, commonly found across North America, Europe and many other parts of the world | Eastern North America: southeastern Canada (southern Ontario to the Maritimes) and the eastern United States south to northern Florida and west to the Great Plains, most common in the Northeast. |
| Active | Active year-round in heated buildings; outdoors most active spring through autumn and mainly nocturnal | Most active spring through early fall; nocturnal and crepuscular (active at night and twilight). |
| Pest? | Yes | No |
🔍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)
🔍How to spot a northern black widow
- Glossy, rounded black abdomen on females with a red hourglass on the underside that is usually split into two parts.
- Females larger and more bulbous than males; males are smaller, slimmer and more patterned.
- Irregular, tangled cobwebs in sheltered, low locations like woodpiles, sheds, and basements.
- A row of red spots on the top of the abdomen and a broken hourglass point to the northern black widow; a complete hourglass and no dorsal spots suggest the southern black widow.
?Frequently asked questions
What is the difference between a false black widow and a northern black widow?
False widows (Steatoda) are usually brown to purplish-black with paler markings and no red hourglass; their bites are generally far less severe.
Is a false black widow or a northern black widow more dangerous?
False black widow: Venomous bite. Northern black widow: Venomous bite. Bites are uncommon and usually occur when a spider is pressed against skin. Bites inject neurotoxic venom that can cause latrodectism: pain spreading from the bite, sweating, nausea, muscle cramps and abdominal rigidity, sometimes with raised blood pressure.
Identification from photos is never certain: don't handle insects you can't identify, and get medical advice for bites, stings or allergic reactions.