Eater of Worlds

The Eater of Worlds is a Boss monster summoned by using Worm Food in The Corruption. If the food is used anywhere else than in The Corruption the user will instantly die by taking 950 damage. Furthermore if the player uses Worm Food when he/she's already fighting The Eater of Worlds the player will take 7000 points of damage.

A large worm with a body comprised of several Devourer connected to each other.

Spawns after breaking 3 Shadow Orbs or luring him out with a Worm Food

Drops a piece of Shadow Armor and a lot of Demonite and Shadow Scales.

Strategy
The Eater of Worlds acts like a larger Giant Worm, digging through the ground always trying to ram the player, will most of the time be in the ground. Because of its large size and how his body sticks together as many weak parts, a Vilethorn is highly recommended to be brought to the fight, as the player can attack multiple parts of his body at the same time doing tremendous damage.

If you kill a part of its body it will split into a second worm and will keep dividing every time it happens. The more worms out the harder he is. The smallest size it can split into are 3 units and killing any part of that worm then will kill it. The Eater of Worlds are defeated once you kill all off them. After it is defeated, it will drop items such as a piece of Shadow Armor, a lot of Demonite and Shadow Scales.

Failing to kill the eater of worlds will result in the creature chasing you back to spawn. While it seems like he will relentlessly fight you until you kill him, he will after some time eventually disappear if you keep dying to him ("Eater of Worlds is Defeated!" message with no loot dropped).

Standing on a wide, elevated platform (with either glass or sky below it) helps tremendously, as you can see him approaching from below.