Bufonid toads possess toxic compounds during most phases of their life cycle that render them unpalatable to many predators. However, snakes of several genera, including Thamnophis, frequently feed on toads and are apparently resistant to their toxins. When approached by garter snakes (T. s. sirtalis), toads (Bufo a. americanus) crouch and usually become immobile; visual stimuli are required to elicit these responses. Toads contacted by the main trunk (body) of a snake usually remain immobile and thus undetected by the snake; toads contacted by the head of a snake usually respond by hopping away and crouching again. The survival rates of toads exhibiting the species-typical response (i.e., hopping when contacted by the head of a snake and remaining immobile when contacted by the body of a snake) are significantly higher than those that respond with the alternative behavior.