Aquatic insects must get
oxygen while they are under water.
Almost all animals require a source of oxygen to live. Insects draw air into their bodies through
spiracles, holes found along the sides of the
abdomen. These spiracles are connected to
tracheal tubes where oxygen can be absorbed. All aquatic insects have become adapted to their environment with the specialization of these structures, enabling: • Simple diffusion over a relatively thin
integument • Temporary use of an air bubble • Extraction of oxygen from water using a
plastron or
blood gill • Storage of oxygen in
hemoglobin and
hemocyanin molecules in
hemolymph • Taking oxygen from surface via breathing tubes (
siphons) The nymphs of the
hemimetabolous orders mayflies, dragonflies and stoneflies, and the larvae of the
holometabolous orders
megalopterans and caddisflies, possess tracheal gills, which are outgrowths of the body wall containing a dense network of tracheae covered by a thin cuticle through which oxygen in the water can diffuse. Some insects have densely packed hairs (
setae) around the spiracles that allow air to remain near, while keeping water away from, the body. The trachea open through spiracles into this air film, allowing access to oxygen. In many such cases, when the insect dives into the water, it carries a layer of air over parts of its surface, and breathes using this trapped air bubble until it is depleted, then returns to the surface to repeat the process. Other types of insects have a
plastron or physical gill that can be various combinations of hairs, scales, and undulations projecting from the cuticle, which hold a thin layer of air along the outer surface of the body. In these insects, the volume of the film is small enough, and their respiration slow enough, that
diffusion from the surrounding water is enough to replenish the oxygen in the pocket of air as fast as it is used. The large proportion of
nitrogen in the air dissolves in water slowly and maintains the gas volume, supporting oxygen diffusion. Insects of this type only rarely need to replenish their supply of air. Other aquatic insects can remain under water for long periods due to high concentrations of hemoglobin in their hemolymph circulating freely within their body. Hemoglobin bonds strongly to oxygen molecules. A few insects such as
water scorpions and
mosquito larvae have breathing tubes ("siphons") with the opening surrounded by
hydrofuge hairs, allowing them to breathe without having to leave the water. == Locomotion ==