Final answer:
Insects use spiracles connected to the tracheal system for gas exchange, a highly efficient respiratory system made up of tubes that transport oxygen directly to body tissues.
Step-by-step explanation:
Insects exchange gases through pores called spiracles, which connect to an internal system of tubes called tracheae, which in turn are connected to respiring tissues. Insect bodies have these spiracles along their thorax and abdomen, allowing for the efficient passage of oxygen into the body and regulating the diffusion of CO₂ and water vapor. The tracheal system is a highly specialized and direct respiratory system, consisting of chitin tubes that carry oxygen to the entire body, independent of the insect's circulatory system.
This respiratory system works well not only in terrestrial environments but also in freshwater aquatic environments. However, no insects live entirely in marine environments. The tracheae within this system branch throughout the body, ending in minute tracheoles that perform gas exchange directly between the air and cells, illustrating an evolutionarily significant adaptation for terrestrial life in hexapods, myriapods, and arachnids.