Worm AI

Worm AI is an AI type followed mostly by long enemies with multiple segments.

Behavior
An NPC with the Worm AI exhibits the following behavior:
 * Can pass through all solid blocks
 * Unaffected by liquids
 * Immune to knockback
 * Drops loot from the head segments (except The Destroyer, who drops loot from the closest segment to the player /  on the player)

Tips

 * Weapons that are capable of piercing enemies, like Flying Dragon, Rainbow Gun, or Death Sickle, are exceptionally effective against all types of worms.

Trivia

 * It is the only AI that is used by both non-boss enemies and bosses (Eater of Worlds and The Destroyer).

Reference
Wurm-KI