The safest way of dispatching an Earth Digger and its variations is with a ranged weapon, such as Xiao's slingshot. The weapon is able to hurt the creature, even when it is underground and from a far enough distance, you can chip away at it's health without fear of retaliation. In the event that you are forced to confront the creature with a melee character, then you need to keep in mind that timing and distance is the key.