Why do female black widows eat there mate after mating?

AnswerIt is not a prerequisite for the female to eat the male, in fact there are many instances where the male escapes unharmed. While tending its eggs the female considers anything on its web that is smaller than it to be prey and simply does not want to miss out on a meal or potential food source for it's young. They are solitary insects and have no contact with the male of the species except when it's eggs need to be fertilized.