Such a relationship has lasted for around 120 million years. The head of the butterfly contains the most sensory structures, including the antennae, eyes, and mouth parts. The antennae are complex sense organs that can detect air movement, humidity and odors. The Johnston's organs, located at the base of the antennae, are used for orientation during flight. Adult butterflies have compound eyes with as many as 6000 different lenses, which are ideal for detecting movement.
Caterpillars have around twelve ocelli and no compound eyes.
Adult butterflies have a sucking mouthpart called a proboscis to aid in nutrient uptake. The butterfly's thorax contains the legs and wings. Butterflies have three pairs of legs, two of which may be smaller and held close to the body, called brush-feet. Legs are functional for sense as well as movement, and contain sensory cells to locate host plants. The veination is used in classi- fication.