Another egg case from my Black Widow spider just hatched. Notice that the babies are brown and white, instead of the characteristic shiny black with red markings. Why?
The black and red color of the adult is warning coloration, letting potential predators know that the spider can inflict a painful bite. The babies are not dangerous. If they had the warning coloration, predators would soon consider the colors as an advertisement for a tasty snack instead of a warning. By being more visible, more of the young would be eaten. Instead, the baby spiders have colors that make them better at hiding. Once they grow larger, they will develop the characteristic Black Widow colors.