[header] How to identify a black widow spider [title] Look for red markings on female black widows. [step] Female black widows are best known for the red spots on their bellies. A black widow may have a connected red hourglass shape on the underbelly, or two triangles that don't touch in a slight hourglass shape. 
[substeps] One type of black widow has a row of reddish dots instead of the hourglass shape that the species is known for. There is a lot of variation in the coloring of black widows.