A comparative study of grooming in colubrid snakes

Grooming behavior (head rubbing) of five species of colubrid snakes was observed in order to gain a greater understanding of the topography, phylogeny, sensory control and function of the behavior. The species Thamnophis sirtalis, Thamnophis butleri, Thamnophis melanogaster, Storeria dekayi, and Cyclophiops semicarinatus, were chosen based upon phylogenetic relationships and natural diets. Each species was observed consuming earthworms; head rubbing behavior predictably followed ingestion. Three forms of head rubbing were identified, including two forms of labial rubbing and one form of rostral area rubbing that is hypothesized to function in foraging as well as grooming. Two controlled experiments were performed, one using multiple feedings with either normal or immobilized earthworms, and the other allowing snakes to contact surface secretions of earthworms and purified mucin without contacting the worm. Snakes showed a significantly greater number of head rubs when consuming active earthworms than when consuming immobilized worms. The subjects also had a greater number of head rubs in response to earthworm mucus than to either earthworm surface wash or mucin. It is concluded that the physical properties of earthworm mucus (adhesiveness) stimulate head rubbing behavior. Mouth gaping behavior was found to covary with head rubbing, and it is proposed that tactile cues associated with gaping behavior are a possible sensory modality regulating head rubbing. In addition to the removal of substances that physically interfere with normal movement, other postulated functions of head rubbing are prevention of habituating to prey chemoattractants and of alarming subsequent prey items to the snake's presence. Differences were found among the species based upon natural diet and phylogenetic relatedness: the rostral scale mb was absent in both Thamnophis melanogaster,/em> and Cyclophiops semicarinatus, and the earthworm specialist, Thamnophis butleri, was found to be less sensitive to the parameters of predator-prey interaction than the other species. These findings are generally consistent with findings of phylogenetic conservatism and contextual stimulation of grooming behavior in other taxa.