Egg sacs are oval, brown, papery and about inch long. They hold from 25 to 750 or more eggs, which have an incubation period of 20 days. Newly hatched spiders are predominately white or yellowish-white, gradually acquiring more black and varying amounts of red and white with each molt. Growth requires two to three months, with older females dying in autumn after egg laying. The female black widow stores sperm, producing more egg sacs without mating.
Some females live more than three years.
You may not always feel the black widow spider bite at first. The first sign of a bite is a small local swelling. There may be two small red spots in the center of the swelling. After three hours or so, the site of the bite becomes more painful. Common reactions include an overall ache of the body, in particular the legs.