What Organs Are Used in the Respiratory Systems of Insects

Unlike humans and other vertebrates, insects do not breathe by filling up a pair of lungs. The only similarity between insect and vertebrate respiration is the branching tracheal system that transports oxygen from the outside world to the inner cells. For insects, oxygen is drawn in not through the mouth, but through tiny openings in the body called spiracles.

  1. How Spiracles Work

    • Spiracles are the tiny openings found on the thoraxes and abdomens of insects. Open spiracles let air in passively, allowing the insect to breathe without having to actively respire. Unfortunately, open spiracles can lead to evaporation of the insect's bodily fluids in dry environments, or flooding of the insect's trachea in watery environments. For these reasons, some insects pinch their spiracles closed with specialized muscles to either keep water in or shut it out.

    The Tracheal System

    • Air first enters the insect's body through tracheal trunks. These trunks are the only parts of the tracheal system directly connected to the spiracles. Deeper in the insect's body, the tracheal trunks branch out into smaller tracheal tubes. The tracheal tubes continue to branch until they reach the inner cells. Spiraling through most trachea are supportive fibers called taenidia. The taenidia keep the trachea from collapsing under pressure, which would restrict airflow.

    Air Sacs

    • Where taenidia are not present in the trachea, the membranes are allowed to expand and collapse more easily. This leads to the formation of small air sacs that can be squeezed shut or inflated with air, depending on the insect's needs. A diving insect, for instance, needs to close its spiracles to avoid drowning. With no outside oxygen available, the insect relies on air stored in its air sacs to survive under water. Conversely, air sacs can deflate to make room for growth.

    Tracheoles

    • The tracheal system ends in fluid filled membranes called tracheoles. Tracheoles reach deep into the insect, delivering oxygen to muscles and other living cells and exchanging it for carbon dioxide. The water in tracheoles facilitates the movement of gasses through the process of diffusion. The movement of oxygen gas also depletes the water supply of the tracheoles. This means that a resting cell has more fluid in its tracheoles than an active cell.