Lamia

The Lamia is a creature from ancient Greek mythology. The story says that the Lamia was a beautiful Libyan Queen who the god, Zeus, fell in love with. Hera, Zeus' wife became jealous of the queen and cursed her to become a child-eating monster. Where some accounts say that her face became distorted and hideous because of the evil she committed, some say she is still the beautiful woman that seduced the great god and captured his heart.
The Lamia is said to be half human, half serpent. She has a serpents tail from the waist down and the upper half of her is the woman that Hera cursed from her rage.
Later interpretations of the myth describe a number of Lamia who act like Succubi, who seduce young men and feed on their blood like a sort of vampire. In this interpretation, their venom is thought to be highly poisonous. There are accounts of male Lamia and even hermaphrodites.
Part of the curse that Hera placed upon the Libyan queen was that of being unable to close her eyes. This meant that she could never rest or sleep. Zeus took pity on her and made her able to take out her eyes. This, at least, enabled her some rest. However she is unable to sleep. She's described as night-haunting, suggesting that she was sort of nocturnal.