A black widow female generally lays eggs during the spring and summer months. In order to lay her eggs, she will construct whitish-colored, silky egg sacs, which are tightly woven and strong. These are usually rounded or pear-shaped. After a short time, the sacs will turn from white to tan. After constructing a sac, which takes a female a couple of hours, she will deposit anywhere from 25 to 250 eggs in it.
The egg sacs are suspended from the spider's web, which is located in dark, undisturbed areas like woodpiles, under rocks, or in outbuildings like sheds. The female fiercely guards her eggs and is more likely to attack a perceived predator during this time.
The spiders will emerge from the egg sac after about a month. These newly hatched spiders are called spiderlings. Because the egg sac may contain hundreds of eggs, hundreds of spiderlings will hatch, however, many of these will not survive because black widow spiders will eat one another in the early stage of their life.
A female black widow is able to store sperm after mating and is therefore able to lay more eggs without mating again.