These hides are skinned on killing the monster, thus no tools are required. Instead, the player must be able to comfortably kill the Mouseling Grunts.
They can be used to craft Mouseling Leather, which is used for various leather type equipment. It is also a decent source of money in early-game if the player is new to Life Forge. However, the player should have a decent amount of defense or be good at attacking from afar if they want to survive trying to kill multiple Mouseling Grunts, since movement speed can be slowed pretty quickly due to the lack of Strength to carry a ton of hides.
Tanning: 5 Mouseling Hide -> 1 Mouseling Leather