In French folklore, the Guivre was a serpentine (e.g. wingless) dragon. It had very poisonous breath that withered grass and caused virulent plagues and diseases in anyone who breathed in the foul fumes. The Guivre also appeared in medieval heraldry. Guivre was the Old French word for "viper". The Wyvern was considered an English import of the Guivre.