Eater of Worlds

The Eater of Worlds is one of thirteen boss enemies. It is a giant Corruption-themed worm (resembling a Devourer, but much larger) with eyes. It is summoned using the Worm Food from within The Corruption, or by destroying 3 Shadow Orbs.

The Eater of Worlds is not a single target, but a string of 50 body segments with individual life counters. When any inner segment is destroyed, it splits into multiple smaller worms, each with their own head and tail. Each section of the Worm must be killed in order to defeat the entire boss.

Fighting the Eater of Worlds is the only way to obtain Shadow Scale, which are required to craft the Nightmare Pickaxe, The Breaker, and Shadow Armor. Defeating the Eater of Worlds also produces usable quantities of Demonite Ore. Individual segments drop some of these when killed, with a larger bonus drop upon defeating the entire entity.

Tips

 * Farming the Eater of Worlds is one of the most effective ways of making money prior to Hardmode. Mid-game armor and weapons will make the fight easy, and selling its drops will yield 9 to 11 each time, on average. After hardmode, is also the easiest way of farming soul of night. Every eater killed will give you 4-5 souls, and lots of hearts it drops. It makes you nearly invulnerable to all the other enemies that may spawn. The eater can also be summoned while killing other bosses to heal youself fast.
 * Weapons that pierce for multiple hits are effective, due to the Eater's large size (eg. Flails, Spears, Spiky Balls, Vilethorn). The Harpoon is also effective, and is best used when being charged by his head.
 * When you kill a section of the Eater of Worlds, they will drop hearts if the player is injured, as if it was another enemy. The near-constant hearts will heal the player, making the battle not as challenging as you may think.
 * The Eater of Worlds is very useful for farming the Corruption Key to open the Corruption Chest in the Dungeon.

History
Dévoreur de Mondes Eater of Worlds Пожиратель миров