Equip the Dark Silver shield (can be won from Garl Vinland at last area of World 5). The Maneaters' snake tails will occasionally imbue them with a yellow power. If you stand directly in front of them and guard when the snake rises above the rest of the creature, the flash of yellow will temporarily blind the Maneater, allowing for one or two heavy hits before dodging to safety. It is not known if this works with other shields.