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For a comparative study of facial grooming behavior, we selected five species of colubrid snakes (Thamnophis sirtalis, T. butleri, T. melanogaster, Storeria dekayi, and Cyclophiops semicarinatus) based upon their phylogenetic relationships and natural diets. In an initial descriptive study, head-rubbing behavior reliably followed ingestion of earthworms in all five species. Three forms of head rubbing were identified, including two forms of labial rubbing and one form of rostral area rubbing. The latter occurs during foraging as well as grooming. Two additional controlled experiments were then performed. One experiment assessed the effects of multiple feedings with either normal or immobilized earthworms. The second tested the effects of allowing snakes to contact surface secretions of earthworms and purified mucin without physically contacting the worm. The snakes showed a significantly greater number of head rubs when consuming active earthworms than when consuming immobilized worms, and this increased over the five trials. The snakes also head rubbed more frequently in response to earthworm mucus than to either earthworm surface wash or diluted mucin. The physical properties of earthworm mucus (adhesiveness) thus seem to stimulate head-rubbing behavior. Differences in head rubbing among the species are discussed in relation to natural diet and phylogenetic relatedness. Furthermore, mouth gaping often occurred with head rubbing and can be distinguished from yawning. Tactile and kinesthetic cues associated with this gaping behavior may aid in regulating the occurrence of head rubbing. Neonate snakes head rubbed in a species-typical manner.