As larvae, Spicebush Swallowtails have two stages of mimicry. While the larvae are in the early stages, they are dark brown in color and thus appear to resemble bird droppings, which encourages predators to leave them alone. When the larvae have progressed to their fourth and last instar and are nearly ready to pupate, they turn a yellow-green color and are marked by two large black dots with a white highlight. The placement of these dots on the swollen thorax creates the illusion that the caterpillars are common green snakes. Mimicking snakes help the caterpillars to ward off predators, specifically birds. The caterpillar Spicebush Swallowtails enhance the physical resemblance behaviorally, as they have been observed to "rear up and retract the actual caterpillar head."