Aquatic insects

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A water beetle

A whirligig beetle

Aquatic insects live some portion of their life cycle in the water. They feed in the same ways as other Insects. Some diving insects, such as predaceous diving beetles, can hunt for food underwater where land-living insects cannot compete.

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
# Breathe from bubble
# Breathe using a plastron
# Extract oxygen using a "gill"
# Storage of oxygen in hemoglobin molecules

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 larvaes 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.

Though not as complex as the gills of a fish, some aquatic insects have modified structures extending from the trachea which allow the organism to exchange gases with the environment. Oxygen diffuses from the water into these gills and moves from there through the gills to the insect’s body. Other aquatic insects can remain under water for longer periods due to a storage of oxygen. Insect hemoglobin has a strong attraction to oxygen molecules, and is carried in the hemolymph which circulates freely with the animal’s body.

References

Drees, B.M. and Jackman, John, (1999), “Diving Beetle” in Field Guide to Texas Insects. Gulf Publishing Company, Houston, Texas. (see http://insects.tamu.edu/fieldguide/bimg133.html)

Stanley, D. and Bedick, J. (1997). Respiration in aquatic insects. Retrieved Dec 27, 2003 from http://entomology.unl.edu/ent801/aqresp.html

Hutchinson, Robert (1998). Adaptations seen in insects for living in or on water. Retrieved Dec 27, 2003 from http://www.roberth.u-net.com/waterinsect.htm
Farb,Peter (1962). The Water Dwellers [LIFE]INSECTS pg.142

External links

[Insect stages] - "Some larvae, nymphs and adult insects that live in freshwater." A UK-based web site with microscopic photos of various insects and other microorganisms as well as biological information.

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