Beneath the water of desert wells, you can find a special "worm altar" block. Using a fishing rod on the water above will cause the player to reel in a giant worm beast.
The altar is destroyed and the Irthwurm leaps into the air only to burrow back into the ground. It will move around the player under the surface and jump out into the air to dive down and attack the player. Wherever the Wurm lands, it will cause a ripple effect in the sand which will make players within range fall into the sand and suffocate.
As the Irthwurm disappears under the sand, the player should bring Spectral Arrows in order to track the creature. When the Irthwurm is about to surface, sand particles will shake on the ground and a rumbling sound will occur.
Drops: Upon death, the Irthwurm drops lapis lazuli and a Sandy Scale.
Image of the Irthwurm: