The venom from a black widow bite initially causes pain, swelling and redness at the injection site, according to LiveScience.com. After about an hour, pain similar to a dull muscle ache can spread throughout the entire body.
LiveScience.com further explains that symptoms normally seen with a black widow bite also include sweating, nausea and headaches. In severe cases, the victim may have trouble breathing and can experience muscle weakness and stiffness, especially in the abdominal area. Pain from a bite lasts several hours while the other symptoms continue for up to a week.
Black widow bites are rarely fatal, according to Wikipedia. However, individuals who are very young, elderly or ill should immediately seek emergency medical attention when bitten.