Caterpillar of the giant swallowtail, Papilio cresphontes, with its scent horns (osmateria) extended. Early stages resemble a fresh bird dropping and this caterpillar is highly dependent upon its camouflage for protection, but when disturbed it extends its normally hidden scent horns. They produce a foul smelling substance that is thought to deter predation. Giant swallowtail butterfliesh are found over a large portion of the southeastern US, west and south into much of South America. During summer it extends its range northward as far as Canada. Photo, Dallas, TX on a citrus, a plant that this caterpillar is often a pest of. In citrus growing regions this caterpillar is often known as the "orange dog".