Widows are so named because of the cannibalistic behavior that they exhibit during the mating process. After mating is complete, the male is sometimes killed and consumed. Cannibalism is further witnessed in the spiderling stage. Females will lay hundreds of eggs, but very few young will hatch and actually survive to adulthood due to consumption of one another.
Black Widows typically feed off of other insects, capturing them in their extremely strong webs and then injecting the prey with enzymes that will liquefy their insides. The spiders are then able to drink up the fluids.