Radscorpion

Radscorpions - "They seem to be extremely large versions of the north American Emperor scorpion. Contrary to my medical knowledge, their poison has grown more potent, not diluted, as I would expect."  "They seem to be sensitive to light.  Nocturnal."  -  Razlo of Shady Sands.

Samples of poison from their tail can be used to make Antidotes.

Appearances in Fallout games
Radscorpions can be encountered in all Fallout games.