BitSpawn's puzzle 69 scorpion toxin from puzzle 1077. All three revisiting puzzles here are four-bridge long-chain toxins with similar structures.
Scorpion toxin in Foldit refers to a series of revisiting puzzles involving toxins found in scorpion venom.
Revisiting puzzle 55: Scorpion Toxin presents a toxin from Androctonus australis.
Revisiting puzzle 57: Beta-Neurotoxin presents a puzzle 55-like toxin from Centruroides sculpturatus.
Revisiting puzzle 69: Scorpion Toxin presents a toxin form Hottentotta judaicus.
In addition to these revisiting puzzles, which have appeared several times, there were different scorpion toxins in early puzzles. See Scorpion Toxin for a toxin which appeared as a "New Player Puzzle" at least once. New player puzzles have since been discontinued.