The Eater of Worlds is similar to the Devourer but with more health, and splits into smaller worms as it takes damage. It appears to be made out of multiple Eaters of Souls which are linked to each other.
The Eater of Worlds is summoned with Worm Bait, which is made with Rotten Chunks (which are dropped by Eater of Souls) and Vile Powder (which is made from Vile Mushrooms found in corrupted areas). It must be summoned in The Corruption, otherwise you are killed instantly.
Each segment of the Eater of Worlds has 200 HP.
To defeat this boss, one must destroy each and every individual Eater of Souls that makes up its body, it is pretty simple to dodge them, just keep moving around. Weapons like Ball 'O Hurt, Blue Moon, Vilethorn (if you have mana) and fast swords like Muramasa and Blade of Grass are good choices. Damaging more than one part at time is the secret for a rapid killing without many Healing Potions. When defeated, a message will be displayed signaling the boss battle is over.