In folklore, a werewolf, or occasionally lycanthrope, is an individual who can shapeshift into a wolf or therianthropic hybrid wolf–humanlike creature, either voluntarily or involuntarily due to a curse or other affliction. In modern fiction, especially film, transformations are often depicted as triggered by the full moon and transmitted by a bite or scratch from another werewolf. Early sources for belief in this ability or affliction, called lycanthropy, are Petronius (27–66) and Gervase of Tilbury (1150–1228).