diagram of a spiracle

Air flow into the spiracles is regulated by small muscles that operate the valves within each spiracle. The muscles contract to close the spiracle and relax to open it.

The morphology of spiracles can vary between insect species. In some species spiracles may be simple valvular openings while in others it may be a more complex structure with increased functionality. For example, fruit flies have the ability to control the size of their spiracles which enables them to reduce the loss of moisture from their bodies in dry climates. In some species, the spiracles may possess hairs which function as a filter system to prevent entry of debris into the tracheal system.