Anomura Fungus

The Anomura Fungus is an insect like creature that spawns in underground or surface mushroom biomes during a Blood Moon. However they tend to spawn rarely on surface mushroom biomes without a Blood Moon along with some other mushroom enemies. Their spawn rate increases and can spawn at any time in hardmode.

Trivia
Anomura is an order of crustacean with some species similar in looks to this creature.