Spiracle
기문
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<speciesfyi-glossary slug="spiracle"></speciesfyi-glossary>Definition
A small opening on the body surface of insects through which air enters the tracheal respiratory system.
Detailed Explanation
Insects lack lungs — oxygen diffuses passively through spiracles into a branching system of air tubes (tracheae) that reach directly to cells. This limits body size in insects, as diffusion efficiency decreases with distance. During the Carboniferous period, higher atmospheric oxygen concentrations (up to 35%) may have allowed giant insects like Meganeura (dragonfly with 70 cm wingspan) to evolve. Aquatic insect larvae often have gills instead of spiracles.