Male and female black widows look different. In all cases, "the females are the most distinctive, with shiny black bodies and a red hourglass-shaped marking on the underside of their round abdomen," said Jo-Anne Nina Sewlal, an arachnologist at the University of the West Indies in Trinidad. The hourglass marking can, on occasion, also be orange-yellow.
Female black widows are about 1.5 inches long. The males are about half the size of females. Males are lighter in color, with red or pink spots on their backs, according to the North Carolina Cooperative Extension Service at North Carolina State University