Minibeast Profiles: Aquatic Insects
by Gary A. Dunn.M.S., F.R.E.S., Director of Education
As the largest group of animals, the insects use practically every type of watery (aquatic) habitat that is available. There are insects that live in, on or near both fresh water and saltwater, including some ocean surfaces, salt marshes, salt lakes, mineral springs, thermal pools, puddles, alpine pools, roadside ditches, tree holes, pitcher plant leaves, freshwater marshes, swamps, pond and lakes, underground streams in caves, brooks, creeks, streams and rivers. Only the ocean depths and the deepest freshwater lakes are void of insects.
Adult mayfly
Some of the insect orders are completely aquatic, meaning all members of the order spend at least one of stage of their life in the water. The common "aquatic orders" include the mayflies (order Ephemeroptera), dragonflies and damselflies (order Odonata), stoneflies(order Plecoptera), and caddisflies (order Trichoptera). Some of the other insects orders contain one or more families that are aquatic or semi-aquatic for all or part of their life. For example, in the springtails (order Collembola) there are several families with aquatic species. In the true bugs (order Hemiptera) there are water boatmen, backswimmers, marsh treaders, water striders, ripple bugs, giant water bugs, waterscorpions, velvet water bugs, creeping water bugs, and toad bugs. In the Neuroptera there are spongilla flies (they live inside freshwater sponges), dobsonflies, fishflies, and alderflies. In the beetles (order Coleoptera) there are crawling water beetles, whirligigs, predaceous diving beetles, burrowing water beetles, water scavenger beetles, water penny beetles, mud-loving beetles, long-toed water beetles, and riffle beetles. In the true flies (order Diptera) there are mosquitoes, midges, black flies, crane flies, snipe flies, hover flies, and shore flies. There are even some moths (order Lepidoptera) that have aquatic caterpillars.
There are two major problems with an aquatic lifestyle: methods of locomotion and sources of air (oxygen). There are actually two different problems when it comes to locomotion, namely, staying put in swiftly moving water and moving about in still water! Insects that inhabit swiftly flowing waters use a variety of "anchors" to stay in one place. They may use their claws as hooks, glue themselves to rocks, use suction cups, or hold themselves down with pebbles or sticks. Insects that live in still waters move around by swimming with legs shaped like paddles, wiggling their bodies, or shooting spurts of water out of their hind end.
The ways that aquatic insects get their air for breathing depends on where they live. Insects that live on the surface of the water generally have no problem getting air. Those insects that live near the surface but spend lots of time swimming beneath the surface of the water may use special breathing tubes ("snorkeling") or carry an air bubble trapped around the outside of the body ("scuba diving"). Some insects spend all of their time under water and they are able to take dissolved oxygen right out of the water with their tracheal gills.
PROFILES OF COMMON AQUATIC INSECTS
At certain times of the year, you may notice an odd insect or two attracted to an outside light. Occasionally aquatic insects such as these are considered an annoyance, but usually the problem does not last long. The following are four of the more common aquatic insects that attract attention because of their size, shape, or numbers. They are aquatic because their immature stages live in water.
DOBSONFLIES. The most spectacular of these insects is the dobsonfly Corydalus cornutus, having a wing spread of 4 to 5 inches. It is usually found near water, but at night it may be attracted some distance to bright lights. The wings of both males and females are net-veined, and the mandibles (jaws) of the female are inconspicuous, while those of the male are long and sickle-like.
The larvae, called hellgrammites, are found under stones in swift moving streams and are used by fishermen for bait. Before you try them for bait - remember these insects have strong jaws and can inflict a painful bite. The larvae may live for three years before transforming to adults and may be as long as 2 or 3 inches when full grown. Hellgrammites are predaceous insects feeding on small aquatic life.
MAYFLIES. Mayflies are soft-bodied, slender insects that may be seen moving in great clouds moving across streams and lakes at twilight in an up and down motion mating dance. Fishermen model many "dry flies" after these fragile insects. The adults have two or three long tail filaments and may be seen attracted to lights in the early evening. Generally the adults hide in trees and shrubs close to aquatic areas until the mating flight. Hundreds of these insects move off the vegetation and into the air, fly about 1/2 hour during which time some of them mate, and then return to vegetation for cover or to the surface of the water to lay eggs.
The nymphs live in clear fresh waters and feed on vegetable matter including diatoms and desmids (which make the gold-green color upon stones of the brook bottom). They will also feed on soft tissues of larger plants, either alive or dead.
MIDGES. Aquatic midges (some resemble mosquitoes, but they do not bite) often occur in large swarms. Midges breed in water and under summer conditions several generations may occur each year. Adults are relatively short lived, about 10 days at most. Their presence causes a great annoyance to homeowners who live near the aquatic breeding sites. In some instances they may be so numerous as to cover sides of houses. The males of many species swarm at dusk and mating occur when females enter the swarms. Turning off lights or the use of yellow lights at night when midges are active (dusk and for about 1 hour thereafter) can help reduce the annoyance. Larval stages serve as food for fish in the aquatic habitat.
STONEFLIES. Adult stoneflies are seen near trees, rocks, or other materials. The adults may be attracted to lights at night. They range from 1/2 to 2 inches in length and are dark colored, brown or yellow or pale green. The adults do not fly very far. In contrast to the caddisflies, these insects hold the wings close to the body giving them a flattened appearance. Adults are usually found near water in shady places.
The nymphs are found under stones, around branches, or in debris in the stream bed. Most are vegetarians, feeding on dead organic matter, but a few are predaceous.
When the nymph completes development, it crawls out of the water and takes firm hold on a rock, stick or other nearby object. Very soon it goes through the final molt, the nymphal skin splits right down the center of the back and the adult stonefly emerges. Within a few minutes, the wings are hardened and the insect is ready for flight. The adults live only a few weeks.
CADDISFLIES. The caddisflies are small to medium-sized insects that look somewhat like moths in overall appearance (below, left). The wings are usually held roof-like over the abdomen when the adult insect is at rest. Unlike moths, the wings and body are covered with hairs, not scales.
The larvae are aquatic living in lakes and streams. Most of the larvae construct "portable homes" or cases (above, center and right). Many types of materials are used in the case construction including small stones, sand grains, leaves, sticks, conifer needles and even small snail shells held together by silken threads. The cases are often found attached to vegetation near the aquatic site. The larvae feed on aquatic animals with a few species predaceous on insects, After the larval stage is completed, the insect pupates inside the case and seals the entrance with silk.
-- Carolyn Klass and Edgar M. Raffensperger, Cornell University, Ithaca NY (reprinted from Insect World 11(3), June 1998)
| This educational resource was prepared by the Young Entomologists Society, 6907 West Grand River Ave., Lansing MI 48906-9131, phone/fax 517-886-0630, e-mail YESbugs@aol.com. Support minibeast youth education - join Y.E.S. today! |