How Insect Breathe
Insects lack lungs. Their basic respiratory system is tracheas. Tracheas of insects are aeriferous tubes which end on the sides of the body as small breathing holes (spiracles). Fine-branched parts of tracheae — tracheoles — permeate the entire body, covering organs and even penetrating inside some cells. In this way, oxygen is delivered to the cells of the body, and the gas exchange is ensured without use of the circulatory system.
Many insects living in water (water beetles and true bugs, larvae and pupae of mosquitoes, etc) have to rise to the surface to take in air, i.e. they also have air breathing. Larvae of mosquitoes and some other insects, for the time of renewing the air in the tracheal system, get “hanged” from beneath to the surface of the water with the help of water-resistant hairs.
Water beetles (water scavenger beetles, true water beetles) and true bugs (for example, backswimmers), having breathed at the surface, take on an additional supply of air under their wing covers before they submerge.
In larvae of insects living in water, damp soil, tissues of plants, skin breathing plays a big role.
Well-adapted to water life, larvae of mayflies, caddisflies, and other insects have no open spiracles. They take in oxygen through the surface of all parts of the body where the covering is thin enough, especially through the surface of leaf-shaped outgrowths permeated by a network of tracheas. Larvae of the midge Chironomus also have respiration through the skin — through the whole surface of the body.