While werewolves are the stuff of folklore, the light and the gravitational pull of the Moon do have real effects on the behaviour and physiology of a host of earthbound organisms — including, perhaps, people. Moonlight can also change animal behaviour. Many marine organisms move up and down in the sea depending on the level of moonlight in order to keep their light levels constant. On land, some nocturnal animals come out on a well-lit night to hunt , others stay hidden to avoid predators.