Garden tiger moth spiracle. Coloured scanning electron micrograph (SEM) of a spiracle (air pore, centre) of a garden tiger moth caterpillar (Arctia caja). Air diffuses into the spiracle and is carried around the body by a network of tubes called tracheae. Oxygen diffuses from the tracheae into the caterpillar's tissues and carbon dioxide leaves the tissues and exits the body. Spiracles are found in pairs on either side of most body segments. They are an ingrowth of the chitinous body wall. Magnification: x1130 when printed at 10 centimetres wide.