After mating with a male, the female black widow does actually eat him – simply because he is the closest highly nutritious meal
The male doesn’t seem to mind, in fact, he offers himself to her. He does a little backflip onto his back, exposing his stomach to her fangs, ready for her to tuck in. Normally they are solitary insects and females have no contact with males except for when it’s time to mate.
Sometimes the male will manage to escape unharmed and alive. While the female tends to her eggs, she will consider anything on the web that is smaller then her as prey. The male widow could eat the female in theory, however she is much bigger in size, and stronger. So she is unlikely to be overpowered by the male. The black widow was named after this because she technically becomes a widow once she eats her mate.