Western black widow spiders are small, from 7 to 15 mm long. They have a large abdomen and four small pairs of legs. They are black with a red geometric hourglass pattern on the underside of the abdomen. Females are much larger than males and usually a duller colour.
Cobweb spiders, like all spiders, have eight legs. In most species, the abdomen is marked with colourful patterns that simplify identification. These spiders have “combs” on their hind legs that they use to wrap their prey in layers of silk.
The shapes of the webs woven by these spiders vary greatly from one species to another. The spiders often rest head down on their webs.