Worm AI

Worm AI is an AI type followed by most multi segmented enemies

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

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 a boss (Eater of Worlds).

Reference
Wurm-KI IA Ver 蠕虫 AI