THE INSECT TRACHEAL SYSTEM
Insects, being arthropods, have a relatively inefficient, open circulatory system with no vessels to carry oxygen to different parts of their body. Because of the inefficiency of the circulatory system, a centralized respiratory system, such as lungs, would not meet the respiratory demands of the insect's cells. Instead, insects have evolved a very simple tracheal system that relies on a network of small tubes that channel O₂ directly to the different parts of the body.

The tracheal system is composed of chitin-ringed tubes called tracheae that connect directly to the air through openings in the body wall called spiracles. The tracheae are reinforced with rings of chitin, the same material that makes up the arthropod exoskeleton.

The tracheae branch into smaller and smaller tubes, called tracheoles, that eventually terminate on the plasma membrane of every cell in the insect's body. The tips of the tracheoles are closed and contain fluid. Air enters the tracheae through the spiracles and travels through the tracheoles to the fluid-filled tips, where oxygen diffuses directly from the tracheoles into the cells, and CO₂ diffuses from the cells into the tracheoles.