Western black widow vs Northern black widow
These two are easy to mix up. Here's how to tell a western black widow from a northern black widow, and whether either one bites or stings.
Western black widow
Latrodectus hesperus
Northern black widow
Latrodectus variolus
≠The key differences
Also similar; differs in distribution and some dorsal markings. Expert identification or geographic context helps distinguish species.
Found in western North America; similar in appearance but separated geographically. L. hesperus females often show more prominent dorsal red markings.
⚖︎Side by side
| Western black widow | Northern black widow | |
|---|---|---|
| To humans | Venomous bite | Venomous bite |
| Size | Females 7-13 mm body length; males 3-6 mm body length | Females about 8-13 mm body length; males about 3-6 mm |
| Colours | Black, Red (hourglass), Brown (male/patterns) | Glossy black, Red (hourglass marking), Brown (male) |
| Family | Theridiidae | Theridiidae |
| Habitat | Dry, sheltered sites near the ground or in human structures: woodpiles, sheds, crawl spaces, garages, rock crevices, under ledges and in dense vegetation. | Undisturbed, sheltered locations near the ground: woodpiles, garages, basements, sheds, crawl spaces, hollow logs and under stones or debris. |
| Range | Western North America: western United States, southwestern Canada and parts of northern Mexico | 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 | Spring through fall; most active at night | Most active spring through early fall; nocturnal and crepuscular (active at night and twilight). |
| Pest? | Yes | No |
🔍How to spot a western black widow
- Shiny black, globose abdomen on females with a red or red-orange hourglass marking on the underside
- Females larger (7-13 mm) and more robust than males (3-6 mm); males are often brownish with dorsal patterns
- Irregular, tangled cobwebs in sheltered, low locations (near the ground, under eaves, inside sheds)
- Smooth, glossy abdomen (not notably hairy) and relatively long, slender legs
🔍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 western black widow and a northern black widow?
Also similar; differs in distribution and some dorsal markings. Expert identification or geographic context helps distinguish species. Found in western North America; similar in appearance but separated geographically. L. hesperus females often show more prominent dorsal red markings.
Is a western black widow or a northern black widow more dangerous?
Western black widow: Venomous bite. Northern black widow: Venomous bite. Females are venomous; bites can cause latrodectism (local pain, muscle cramps, sweating, nausea, elevated blood pressure). 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.