Silk moth caterpillar air pore. Polarised light micrograph of a spiracle (air pore, upper centre) and its attached tracheae (air passages) from a silk moth caterpillar (Bombyx mori). Spiracles are found in the exoskeleton of insects. Air diffuses into the spiracles and is carried around the body by a network of tracheae. Oxygen diffuses from the air into the insects' tissues, and carbon dioxide leaves the tissues and exits the body.