Summary
Common house spiders are mottled tan-and-brown; black widows are glossy jet-black with a red ventral hourglass. Their webs and posture are otherwise nearly identical.
Diagnostic traits
| Trait | Common House Spider | Southern Black Widow |
|---|---|---|
| Color | Mottled tan, brown chevrons | Glossy jet-black |
| Hourglass | Absent | Bright red, ventral |
| Body length ♀ | 5–6 mm | 8–13 mm |
| Web posture | Hangs in tangle anywhere | Hangs upside-down in lower tangle |
The bottom line
At-a-glance comparison
| Common House Spider | Southern Black Widow | |
|---|---|---|
| Scientific | Parasteatoda tepidariorum | Latrodectus mactans |
| Family | Theridiidae | Theridiidae |
| ♀ body | 5–8 mm | 8–13 mm |
| Leg span | 20–30 mm | 25–38 mm |
| Range | 1 U.S. states | 23 U.S. states |
| Medical | Low | Medically significant |