Orb-weavers often eat their old webs before spinning new ones! Spider silk is made from protein, so consuming the web returns that protein to the spider’s silk glands, ready to be used another day.
If food is plentiful, the spider doesn’t need to eat its web–which is why you see old, empty orb webs that have been abandoned. But if the spider isn’t eating regularly, it can survive by consuming its web and spinning a new one until it catches a meal.