Birds are common, and in vegetated environments, their numerous droppings commonly are found lying on leaves. Predators typically do not interpret bird droppings as a preferred source of food, so those remains are ignored by foraging animals. For the caterpillar that spends its life feeding on leaves, imitation of bird droppings is a useful mechanism of disguise. Butterflies of the genus Limenitis, such as the red-spotted purple and viceroy, have well developed that mechanism of deception. Compare the caterpillar (left image) with the actual bird dropping (right image).