Black widow spiders have earned a bad rap by supposedly eating the males of their species after mating with them. This is only partially true. Appearantly, mating must take a lot out of the males(true for homosapiens as well?), and if the male is too weak to continue hunting for his food, the female will put him out of his misery so he doesn't starve to death.
Two more facts worth noting are that only female black widows are poisonous, and the male black widows are considerably smaller than the females.