Radscorpions are mutated from the North American Emperor scorpion, which were prolific in many pet stores at the time of the Great War. Contrary to many expectations, their venom grew more potent when they mutated rather than becoming diluted. Though considered nocturnal and sensitive to light, radscorpions can be found active during the daytime in the areas they inhabit. Samples of their venom can be used to make antivenom.
Radscorpions, of all variants, are vicious enemies. They have rock-solid carapaces that can withstand considerable amounts of damage, and their stingers are filled with a potent poison. They almost always gather in packs of at least four individuals and are incredibly deadly to unprepared player characters.
Lesser radscorpions are diminutive when compared to their larger brethren and pose less of a threat. Nonetheless, their stingers still inject deadly radscorpion poison into their foes and as such are dangerous to unprepared travelers.
The nasty radscorpions deal more damage from their stingers and have greater health than regular radscorpions, hence their name. However, they are not as common as their counterparts. They are most often found in caves and during random encounters around the wasteland.
The black radscorpion is a tougher version than the regular radscorpion. They are encountered at higher levels, and they can also be encountered with groups of radscorpions and in caves. They are rare at low levels.
The regular radscorpion appears in both Fallout and Fallout 2. The nasty radscorpion appears only in Fallout and the lesser, the black lesser and the regular black radscorpion appear only in Fallout 2.
↑Razlo dialogue file - "They seem to be extremely large versions of the north American Emperor scorpion."
↑Chris Avellone, Fallout Bible 1 - "The radscorpions are a result of a combination of radiation and the FEV virus, and Razlo in Shady Sands is correct - they were originally Emperor Scorpions that have grown... big."