The scorpion Centruroides vittatus is periodically exposed to freezing temperatures in its natural habitat. It survives such stress by employing physiological mechanisms characteristic of the freeze-tolerant survival strategy used by some insects. Studies over a 12-mo period revealed that scorpions collected in the field and exposed to freezing temperatures in the laboratory froze at high subzero temperatures. High percentages of these animals recovered after freezing. Neither polyols nor thermal hysteresis proteins, which may serve as antifreezes, were found in sufficiently high levels in the hemolymph to substantially lower body supercooling points. Instead, potent ice-nucleating activity compartmentalized in the gut induced ice formation. Ice-nucleating activity peaks in winter months and appears to be proteinaceous. This is the first reported observation of freeze tolerance and ice-nucleating agents in scorpions.