A branching system of air tubes
Insects use a tracheal system to bring respiratory gases directly to tissues where respiration is occurring, rather than relying on a separate transport system to carry the gases to those tissues.
Spiracles are openings in the exoskeleton that connect the external air with larger tubes called tracheae. These divide repeatedly into narrower tracheoles.
Large numbers of tracheoles extend directly to muscle fibres. Their many fine endings provide a large surface area for gas exchange, while their close association with respiring cells gives gases a short diffusion distance.