Common house spider vs False black widow
These two are easy to mix up. Here's how to tell a common house spider from a false black widow, and whether either one bites or stings.
Common house spider
Parasteatoda tepidariorum
False black widow
Steatoda grossa
≠The key differences
Steatoda is usually darker, often more uniformly brown to purplish-brown and may have a smoother, more rounded abdomen; false black widows can be mistaken for Parasteatoda but Steatoda lacks the variable mottled tan patterns and may produce larger, stronger bites in rare cases.
⚖︎Side by side
| Common house spider | False black widow | |
|---|---|---|
| To humans | Mild bite | Venomous bite |
| Size | Females 5-8 mm body length; males 3-6 mm body length | Females 6-10 mm body length; males 4-8 mm |
| Colours | Brown, Tan, Cream, Dark brown | Dark brown, Purplish brown, Pale cream (faint markings) |
| Family | Theridiidae | Theridiidae |
| Habitat | Sheltered indoor and peridomestic sites: corners, ceilings, basements, attics, garages, window frames, behind furniture and under eaves. | Human structures (houses, basements, garages), sheds, under eaves, rock crevices and debris piles |
| Range | Probably native to South America but now cosmopolitan; found across North America, Europe, Asia, and other temperate regions often associated with human structures. | Originally from the Mediterranean and Macaronesia region; now nearly cosmopolitan, commonly found across North America, Europe and many other parts of the world |
| Active | Year-round indoors; most active at night when hunting and maintaining webs. | Active year-round in heated buildings; outdoors most active spring through autumn and mainly nocturnal |
| Pest? | No | Yes |
🔍How to spot a common house spider
- Irregular, three-dimensional tangled web in sheltered indoor corners with a silken retreat.
- Rounded, somewhat bulbous abdomen with variable brown/tan markings.
- Females noticeably larger and more robust than males; males slimmer with visible pedipalps.
- Shorter legs relative to long-legged house spiders; abdomen often patterned rather than uniformly black.
🔍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 common house spider and a false black widow?
Steatoda is usually darker, often more uniformly brown to purplish-brown and may have a smoother, more rounded abdomen; false black widows can be mistaken for Parasteatoda but Steatoda lacks the variable mottled tan patterns and may produce larger, stronger bites in rare cases.
Is a common house spider or a false black widow more dangerous?
Common house spider: Mild bite. False black widow: Venomous bite. Bites are rare and usually occur only if the spider is trapped against skin. 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.