Phasmids are named for their excellent camouflage that makes them almost impossible to see in the wild (Phasmida = "apparition"). Living in temperate and tropical areas all over the world, they are adapted to mimic, or look like twigs or leaves , vanishing into the vegetation. Stick insects are long and brown with bumpy surfaces like bark, while leaf insects are green and flat with ridges like leaf veins. Phasmid behavior supports their camouflage, as they freeze in place or sway from side to side like a leaf in the breeze. Despite their uncanny ability to blend in, phasmids have other defenses at their disposal. Some release noxious chemicals that stink or burn. Some phasmids fall out of trees and play dead. A few species take an opposite approach, making loud sounds and flashing bright colors to startle predators. Phasmids are usually active at night (nocturnal), using their keen eyesight to get around when daytime predators are asleep.