If this site, quoted below, is not expert enough then I'm not sure what you are looking for. Possibly you have your scorpions mixed up? I believe that "most venomous", "potentially fatal", would be a bit more than a "painful reaction". I'm sorry if this was not the information you were looking for. As best I can tell from your question, this is your answer, including the pictures to help identify it.
Bark Scorpion (Centruroides exilicauda)
DESCRIPTION: body (not "tail") up to 2.75" long. Distinguished from other local scorpions by its long, thin pincers (when you're this toxic you don't need strong pincers).
NATURAL HISTORY: Most venomous local scorpion (potentially fatal -- when stung, call the Arizona Poison and Drug Information Center
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