Female black widows are usually dark or black in color with a red or orange hourglass on the bottom of the abdomen or a pair of red spots. They will also have red or red and white markings on the top of the abdomen, either having a single stripe, bars or spots, but some may have no markings at all
Males are half the size of the females. They are grey or brown and usually lighter in color than females. They may or may not have an hourglass marking on their abdomen If they do it will be yellow or white, not red.
Since black widows have latrotoxin in their venom, their bites are potentially dangerous and may result in severe muscle pain, abdominal cramps, and muscle spasms. These effects usually last for 3-7 days.