Self-cannibalism is the practice
of self-eating, also called autocannibalism or autosarcophagy.
Autocannibalism is a mental condition characterized by the practice of eating parts of oneself, such as skin, nails, hair and scabs.

The ancient Ouroboros symbol depicts a snake biting its own tail.

Erysichthon of Greek mythology ate himself in an insatiable hunger given to him as a punishment by Demeter.

In an Arthurian tale,
King Agrestes of Camelot goes mad after slaughtering the Christian disciples of Josephus in his city and eating his own hands.