Aquatic Insects - Breathing

Breathing

One problem that aquatic insects must overcome is how to get oxygen while they are under water. 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.

Aquatic adaptations

1. Simple diffusion over a relatively thin integument
2. Breathing from a plastron or physical gill
3. Extraction of oxygen from water using a plastron or physical gill
4. Storage of oxygen in hemoglobin molecules in hemolymph
5. Taking oxygen from surface via breathing tubes (siphons)

Some insects have densely packed hairs (setae) around the spiracles that allow air to remain near, while keeping water away from, the body. They may even carry a bubble of air down from the surface. Others have a plastron 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. The trachea open through spiracles into this air film, allowing access to oxygen. The larvae and nymphs of mayflies, dragonflies and stoneflies still retain the air tubes they need for adult stage but when in larval stage they are equipped with gills that strain out oxygen in the water.

One mechanism used by some aquatic insects is one or more pockets of air called physical gills or sometimes 'gas gills'. When the insect dives into the water, it carries a layer of air over parts of its surface. The insect absorbs oxygen from this air as it would above the surface. Diffusion from the surrounding water replenishes the oxygen in the pocket of air. The large proportion of nitrogen in the air dissolves in water slowly and maintains the gas gill volume supporting oxygen diffusion. Insects need to periodically replenish their supply of air, not just oxygen.

Other aquatic insects can remain under water for long periods due to high concentrations of hemoglobin in their hemolymph circulating freely within the their body. Hemoglobin bonds strongly to oxygen molecules.