Cave Spirit

Cave spirit is a little dangerous hostile creature that spawns underground in dark areas of all worlds except the biome (not the world) Underground. They can be difficult to spot due to their dark colors and shadowy appearance, but they frequently emit a distinctive growl that can give away their presence.

Characteristics
They have low health and deal low damage. They are particularly threatening early game as they are able to deal about one heart worth of damage to poorly equipped dwarfs before they are killed. They may also attempt to flee after taking a significant amount of damage (when health is lower than 20%). Despite their lack of any appendages, they hover, like beholders, but they do not fly, rather they must jump and climb like other creatures.

They only spawn in areas of very little to no light and have a better chance of spawning in caverns, tunnels or other areas of increased space.

They drop three needles when they die.

Tips
To limit their ability to spawn, ensure your mines are lit. Even a little light may help reduce their ability to spawn.