The Witcher Bestiary - Fleder
Fleder Occurrence: Fleders are lesser vampires which usually hunt in rundown city districts; they are also found near cemeteries and in the wilderness.

Immunity: They are fearless and resistant to stun attempts.

Susceptibility: Sensitive to silver and Vampire Oil.

Tactics: They dive at opponents from the air, try to daze their victims and drink their blood.

Alchemy: Abomination lymph and wing membrane.

Common people believe that fleders are dead heathens who turned into vampires and rose from their graves. Being vampires, they attack sleeping people and drink their blood. According to peasants, a man bitten by a fleder becomes a fleder himself. This is nonsense, obviously.