Tracheal System of a Cockroach

diagram of the tracheal system of a cockrach

The tracheal system of an insect is a complex network of tubes (tracheae) which divide and subdivide into tubes of decreasing diameter. The tracheae eventually branch into microscopic tubes, tracheoles, which are less than 1µ in diameter and penetrate each cell of the body.

The tracheae are epidermal in origin (when an insect moults, the shed exoskeleton sometimes includes old tracheae because it is continuous with the cuticle). Each tracheal tube is lined with a thin strip of cuticle (called taenidia) that winds spirally through the membranous wall. This cuticular reinforcement of the tracheae prevents the collapse of the tracheal walls and also enables each tube to flex and stretch without restricting air flow.

Parts of the tracheal system lack taenidia, facilitating the formation of air sacs which act as reservoirs of air. Insects in dry climates are able to close their spiracles and use the air sacs as a temporary air supply, thus reducing the amount of water lost to the environment. Aquatic insects use the airs sacs as buoyancy regulators as well as an underwater air supply. Moulting insects also rely on their air sacs to inflate their bodies so that they may break free of their old exoskeletons.