When the bubble’s surface area decreases, its rate of gas exchange also decreases. Unfortunately, the size of the bubble shrinks over time as nitrogen slowly diffuses out into the water. An insect can remain under water as long as the volume of oxygen diffusing into the bubble is greater than or equal to the volume of oxygen consumed by the insect. The larger the surface area of the bubble, the more efficiently this system works. In effect, the bubble acts as a “physical gill” - replenishing its supply of oxygen through the physics of passive diffusion. The bubble usually covers one or more spiracles so the insect can “breathe” air from the bubble while submerged.Īn air bubble provides an insect with only a short-term supply of oxygen, but thanks to its unique physical properties, a bubble will also “collect” some of the oxygen molecules dissolved in the surrounding water. This bubble may be held under the elytra (wing covers) or it may be trapped against the body by specialized hairs. Some aquatic insects (diving beetles, for example) carry a bubble of air with them whenever they dive beneath the water surface. mosquitoes) insert their breathing tubes into these air stores and obtain a rich supply of oxygen without ever swimming to the surface of the water. Many aquatic plants maintain their bouyancy by storing oxygen (a waste product of photosynthesis) in special vacuoles. Water scorpions (Hemiptera: Nepidae) and rat-tailed maggots (larvae of a syrphid fly) are two more examples of aquatic insects that have snorkel-like breathing tubes. When the insect dives, water pressure pushes the hairs close together so they seal off the opening and keep water out. At the air-water interface, these hairs break the surface tension of the water and maintain an open airway. An opening at the end of the siphon is guarded by a ring of closely spaced hairs with a waterproof coating. In mosquito larvae, for example, the siphon tube is an extension of the posterior spiracles. A sudden, powerful contraction of the abdomen will expel a jet of water and thrust the insect forward - a quick way to escape from predators.Īlthough many aquatic insects live underwater, they get air straight from the surface through hollow breathing tubes (sometimes called siphons) that work on the same principle as a diver’s snorkel. This rectal gill mechanism doubles as a jet propulsion system. Water is circulated in and out of the anus by muscular contractions of the abdomen. Dragonflies differ from other aquatic insects by having internal gills associated with the rectum. Stoneflies and caddisflies have filamentous gills on the thorax or abdomen.
Fanning movements of the gills keep them in contact with a constant supply of fresh water. In mayflies and damselflies, the gills are leaf-like in shape and located on the sides or rear of the abdomen.
They are covered by a thin layer of cuticle that is permeable to both oxygen and carbon dioxide. In insects, gills are usually outgrowths of the tracheal system. Biological GillsĪ biological gill is an organ that allows dissolved oxygen from the water to pass (by diffusion) into an organism’s body. Larger insects, more active ones, or those living in less oxygenated water may need to rely on other adaptations (see below) to supplement cuticular respiration. Diffusion of gasses through this body wall (cuticular respiration) may be sufficient to meet the metabolic demands of small, inactive insects - More aboutĭissolved Oxygen especially those living in cold, fast-moving streams where there is plenty of dissolved oxygen. Many aquatic species have a relatively thin integument that is permeable to oxygen (and carbon dioxide). Read each of the following sections to learn about these adaptations and how insects use them to obtain oxygen and maintain an aquatic lifestyle. Aquatic insects need oxygen too! They are equipped with a variety of adaptations that allow them to carry a supply of oxygen with them under water or to acquire it directly from their environment.
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