What identifying mark is characteristic of a Black Widow spider?

A distinct red or orange hourglass marking on their underside

The Black Widow spider possesses a unique and reliable visual characteristic used for identification: a distinct marking shaped like an hourglass, typically colored red or orange, located on the underside of its body. This feature is often sought when attempting to identify the species responsible for a bite. The venom from a Black Widow often leads to severe systemic effects, including sharp, radiating pain and abdominal cramping, which develop relatively quickly after the bite occurs, setting it apart from species whose primary danger is localized tissue damage.