Dweller

A  is one of the monster types you'll encounter. It spits an acidic type of bile as a projectile when attacking from a medium range. They have very strong defense making harder to deal damage to them with low-damage weapons. Gatling Turrets are effective against them, and water can be used to slow them down greatly.

Location
You can find Dwellers in the Surface Caverns, under the Grassy Hills.