We investigated the importance of various factors on the defensive behavior of two pitviper species, the cottonmouth and the pigmy rattlesnake: We used cottonmouths in a controlled environment to explore the importance of thermal cues on defensive strike, and the effect of experience with a potential predator on the defensive behavior of adults and neonates. Thermal information was not of importance in eliciting a defensive strike. Adults and neonates differed in their tendencies to habituate to a confrontational but non-harmful stimulus: adults decreased defensiveness over days while neonates did not. The cost of habituation may simply be too high for neonates given their vulnerability. We also analyzed data collected on a population of free-ranging pigmy rattlesnakes: pigmy rattlesnakes were not aggressive as previously concluded. Snakes that were moving struck more frequently than coiled snakes. Fleeing behavior was affected by initial posture of the snake, the age class, and recent feeding.