Insects in Aquatic Ecosystems

Invertebrates are multicellular, eukaryotic heterotrophs that do not have a backbone. A heterotroph is an organism that is dependent on other organisms to provide a source of organic materials that they will consume as food.

There are three growth patterns insects or invertebrates may follow. The first method is molting. The insect born of the egg is like a small replica of parents. It grows by molting. Old skins split when they become too tight and they grow out of them. The second growth pattern is known as incomplete metamorphosis. A nymph comes out of the egg. It looks similar to the adult of the species but is immature, nonproductive and lacks many other important details. In the case of winged insects, nymphs' lack wings. Often these eggs are laid in the water and the young spend their nymph period in water. They are equipped with gills and feed in the water. They molt underwater and when they crawl out of water they emerge as adults. Dragonflies and Damselflies are two examples of insects that undergo incomplete metamorphosis.

Complete metamorphosis occurs when a species grows from an egg to larva to a pupal stage to a sexually mature adult. The growth takes place not by an increase in the number of cells but by an increase in the size of cells. An example of complete metamorphosis would be from an egg to larvae like a caterpillar to chrysalis or pupa to a fully emerged adult like a butterfly.

Invertebrates can be used to indicate the quality of water. Aquatic worms, the lunged snail, the blackfly, leech, and the midge fly can be found in any quality of water. Black ducks enjoy dining on the midge fly.

Species like Crayfish, the Alderfly, Crane Fly, the Riffle Beetle Larvae, the Damselfly, the Sowbug, the Dragonfly, the Watersnipe fly, the Scud, the Whirligig Beetle Larva, and the Fishfly all indicate good to fair quality water. When considering the quality of the water consider species count. For instance, if there is a low number of dragonflies this may indicate that the water is of poor quality.

The Stonefly, the Riffle Beetle Adult, the Gilled Snail, the Planarian, the Mayfly, the Water Penny, Caddisfly and Hellgramite all indicate water that is of good quality.

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