The Eldritch Crab is one of the mobs that can only spawn in the Outer Lands .
The Eldritch Crab is spawned from a crusted opening. The crusted opening has the ability to spawn eldritch crabs in a certain amount of time when the player is within 16 blocks of it. They have 20 health points (10 hearts) and will take up to 3 diamond sword hits to kill. These single-block wide creatures deal a great amount of damage and can be pretty hard to kill. When encountered, they will crawl and leap towards the target and would try to get on their target's head, where they will continue to deal damage. They are hostile against the player, Crimson Clerics and Crimson Knights and will attack any entity that damages it. Occasionally, they will make their entire body almost see through to the point of near invisibility, further increasing their ability to kill.
Upon death, Eldritch crabs can drop an Ender Pearl. Due to them being a common enemy in the maze, champion versions are often encountered.An Eldritch Crab will spawn on the death of a Shambling Husk. This Eldritch Crab wears said husk's mask on its abdomen. This implies that the Shambling Husk is really a knight (perhaps a Crimson Knight) that was killed by the Eldritch Crab, and the crab proceeded to don the knight's helmet and control its body (i.e. make the husk shamble). However, they will never turn a victim into a shambling husk and no official sources talk about this at all.