A black widow spider's life cycle begins as an egg, which is laid by the female in a silky egg sac that she creates. A female may deposit as many as 250 eggs in one sac and will create several of them. Once she lays her eggs, she then stands guard and is more likely to attack during this time.
The young spiders, called spiderlings, will hatch in about a month. Spiderlings molt, or shed their skin, one time inside the sac, then several more times before they fully mature.
The spiderlings initially stay near the sac, but after a few days will climb up to a high area where there is air flow. They will spin silk threads in order to float in the air, which allows them to disperse to a wider area. The entire life cycle of a black widow spider-from egg to adult-takes close to one year.
Young spiders are lighter in color than adults, usually whitish or yellow, but as they mature, they become darker. The pattern on the young spiders of both sexes resembles that of the adult male. They also tend to have one or two reddish spots on the under side of the abdomen. Immature black widow spiders do not have a dangerous bite. It is only the bite of the adult female that is harmful to humans.