Radscorpions are mutated, via radiation and exposure to the FEV virus, 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. Apart from their size, they appear visually identical to normal scorpions, with mottled, dark blueish-gray carapaces.
As radscorpions almost always move in groups of two to five individuals, they can be very dangerous to low level players. Also the addition of Damage Threshold makes them harder to kill for an unprepared Courier. They tend to charge the player character directly and quickly.
Radscorpions take normal damage when shot in the torso, stinger, or claws, and reduced damage when shot in the legs. Unlike other creatures, radscorpions lack a "weak point" that can be targeted for extra damage (they have no "head," for example), which makes V.A.T.S. combat and firearms somewhat less effective against them. Additionally, all radscorpions are armored to some extent, which makes them even more difficult to kill.
Their claws are less-armored than the rest of the carapace; successfully crippling these will stun the radscorpion. Using the Guns skill, the creatures are vulnerable to armor-piercing weaponry. Their tail is also is a formidable weapon, as they use it for poisonous attacks.
These are the most common variety of radscorpion. These poisonous predators seem to possess different speeds, some taking their time and others bolting at top speed. Their size ranges from that of a large dog to that of small livestock.
The smaller and less common variant of radscorpion, these creatures are likely juveniles or a smaller strain of radscorpion, as they are encountered both in the company of larger varieties as well as by themselves.
A larger and much more dangerous variant of radscorpion that is faster, as well as rarer than the usual radscorpion. It does a lot more damage and has a higher Damage Threshold (on par with that of a sentry bot), making them particularly difficult to kill for low level or otherwise poorly equipped players.
Giant radscorpions can be found anywhere that radscorpions will gather or sometimes can be found alone. The player can encounter them very, very early on, since some of them are just outside Goodsprings and Goodsprings Cemetery.
pcps3xbox360 When viewed from a distance, the radscorpion(s) frequently slide vertically across uneven terrain (interfering with V.A.T.S aiming), on the PC version they can also possibly sink into the ground making it near impossible to kill them. If the Courier is unable to kill the sunken radscorpion, it remains as a red tick indicating an enemy on the radar, making it also impossible to leave the area by fast travel. [verified]
pc In the case that a radscorpion has fallen underneath the ground and the Courier's companions have weapons, the follower will attempt to attack the enemy until they either run out of ammunition or the radscorpion is killed by a general area of effect weapon, such as a grenade. [verified]
xbox360 There's a chance that radscorpions, in particular Giant Radscorpions, will freeze in place and not attempt to attack the player when the player comes within their perception range. In this case, any and all types of ranged weapons will deal no damage to them, and the only way of killing the Radscorpion is to use melee or unarmed weapons against it, and/or telling any companions to switch to melee combat.[verification overdue]
↑Razlo dialogue file - "They seem to be extremely large versions of the northIn-game spelling, punctuation and/or grammar 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."