Consumption of the whole or part of a reptile's own shed skin or that of a conspecific (keratophagy) has been documented in 248 species of lizards in 16 families and 19 snakes in four families. There are no authentic cases in turtles or crocodilians. An earlier review based primarily on zoo records noted keratophagy in 160 species of lizards, of which 16 were from literature sources designating field observations or stomach contents. We added an additional 16 captive observations for lizards and brought the total to 89 species for which this behavior has been documented in nature. Eating shed skins of conspecifics has been observed in 23 lizard species in five families. All of the 19 snake species known to have eaten their shed skins, except one, a Clelia clelia, were in captivity. We reviewed six hypotheses that may explain the occurrence and evolution of keratophagy. These are the Nutritional Hypothesis, Skin sensitivity hypothesis, Artificial Behavior Hypothesis in Snakes, Accidental Hypothesis, Predator Avoidance Hypothesis, and the Reduced Parasite Load Hypothesis. The Nutritional and Artificial hypotheses provide the least explanatory power for this behavior. The remaining four hypotheses have varying levels of predictability but each may function within different contexts. We provide recommendations for elucidation of these hypotheses in our discussions of them. Finally, our attempts at electronic searches were hindered because of the variation in the terminology used for this behavior, and because most authors did not include an appropriate term in their list of keywords or in the abstract. We recommend standardization of the term “keratophagy,” and that authors of diet and behavioral studies in which consumption of shed skin was observed include this term in abstracts and key words.
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Vol. 1 • No. 1