Guide:Eater of Worlds strategies

Terrain and Gear
Like all Bosses preparing for the fight is probably the biggest factor in your success:

Standing on a wide, elevated platform (with either glass or sky below it) helps tremendously, as you can see him approaching from below. Further more, since Worms cannot navigate in the air, it will also drastically reduce the Eater of World's mobility. Under such a scenario, the Eater of Worlds can almost always be evaded: Getting hit is often a result of the player's own risk-taking to deal extra damage.

The Platform can further be upgraded with several levels of Wood Platforms, to further increase the player's mobility. Rocket Boots can also help, but are not a requirement.

Good Armor is not a strict necessity, as the Eater of Worlds tends to hit hard, rather than often.

Weapons
Because of its large size and multiple body parts, weapons that can deal damage to multiple sections should be used:Vilethorn, Ball 'O Hurt, Shurikens, Vile Powder, Space Gun, etc... Guns can also be very effective at killing Worms of small size. Also, large swords like the Phaseblade, Blade of Grass and Fiery Greatsword can deal damage evenly if swung repeatedly at the long worm's arcing body.

Note that while weapons like the Ball 'O Hurt tend to damage the Eater of Worlds faster, it will also deal more focused damage, splitting the Eater of Worlds more often. The Ball 'O Hurt is excellent for killing the sub-Worms.

Vile Powder, on the other hand, will not deal its damage as fast (but still very fast), but will have a balanced damage distribution throughout the entire body. Vile Powder has the advantage of being easy to find and free. Furthermore, it is a very safe weapon to use against the worm: It can be placed before dodging the Eater of Worlds and running away, but it will still take damage. It is recommended to have 30 to 150 Vile Powders for this strategy, depending on how conservative you are, and how soon you make the switch from "Damage the Worm" to "Hunt the sub-Worms"

The choice of the weapon will essentially boil down to how safe you want play, or how fast you want to kill the Eater of Worlds.

Using dynamite will instantly kill any parts of the worm hit, providing an extremely fast (but expensive) way to kill the Eater of worlds, If you don't have the proper equipment, It's best to use things with fixed damage like grenades, which are very effective when destroying the main worm.

Managing the Worms
Killing a section of the Eater of Worlds will split into an additional Worms with the Head of the new worm starting where you destroyed the segment. Of course, the more worms that are out, the harder he is. A fundamental strategy when killing the Eater of Worlds is correct management of each sub-Worm. Avoid splitting the Worm when you can. If there are little Worms, concentrate on killing those first, before returning to the main Worm.

Death
Failing to kill the Eater of Worlds will result in the creature chasing you back to spawn, with some delay depending on how far away you were when you were fighting him. He will relentlessly attack until you slay him. After some time he will disappear if you keep dying (an "Eater of Worlds is Defeated!" message will appear with no loot dropped). Occasionally, only one section will follow you if you die, and you can obtain a piece of Shadow Armor relatively easily. (As of patch 1.0.5 the Eater of Worlds will not follow you past corruption)

"Surfing" the Worm
Note that it is much easier to get the Worm to surf by having a two Block wide platform.