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AQUATIC INSECTS
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General information
INSECTS are the most numerous species in the group of invertebrates. During the process of evolution they get used to living in almost every kind of environment, including the water environment. Insects include: dragonflies Odonata, May-flies Ephemeroptera, Plecoptera, Megaloptera, Trichoptera and some species of: Collembola, varied-wing bugs Heteroptera, Planipennia, Diptera, Hymenoptera, Coleoptera and butterflies Lepidoptera. Some insects such as e.g. dragonflies, May-flies or Plecoptera live in the water only as larvae; others such as e.g. water bugs or some cockchafers are connected with water during their adult lives. Adult insects (the so-called imago) breathe the atmospherical air and have to swim up to the water surface from time to time. Larvae of water insects do not receive the oxygen from air but from water by gills' growths, gills-tracheas or by the whole surface of a delicate skin.
Insects play a significant role in the processes occurring in the water environment. Some numerous species are essential elements in the process of circulation and transformation of organic matter - they are the food for many other animals and the predacious species have an influence on the population of other water organisms. Man uses a number of species of water insects to estimate the quality of water (the so-called bioindication). Depending on the specific composition, number and structures of teams of water organisms one can estimate the degree of pollution of the environment where these organisms live. The larvae of stoneflies Plecoptera, May-flies Ephemeroptera and caddisflies Trichoptera are the most sensitive to any pollution and the most useful in bioindication.
The aquatic insects of Wigry National Park live in every kind of reservoirs and water-courses starting from the small, periodically drying pools and drainage ditches to the large lakes and rivers. Despite the common occurrence in nature this group is not recognized to a large degree and will demand some further intensive research.
Stoneflies Plecoptera are insects connected with the flowing waters. They require clean and well-oxygenated water. Adult individuals have a flattened body, long feelers, opaque wings where the back wings are larger than the frontal ones, the abdomen equipped with two twigs. Larvae are similar to adults however they are smaller and they lack the wings. Males die after the act of copulation and females live a bit longer for some time. At this time the female lays from several hundred to about 2 thousand eggs which are attached to the abdomen by means of secretion. Later on the eggs are placed into water. It takes one to three years to become the winged adult insect. All young larvae of Plecoptera eat dead organic matter while older larvae are both herbivorous and carnivorous. Adult insects have retarded mouth organs and during their 4-6 weeks of life they only consume the fat accumulated in the period of life of larva.
Dragonflies and damselflies Odonata - adult individuals are insects of an average or large body size, large eyes, short feelers and often intensive and rich coloration. Dragonflies, both larvae and adult forms, are predacious. Depending on the body size the larvae of dragonflies eat water microorganisms, crustaceans, distomas and other parasite animals, eelworms, water insects, fishes and larvae of amphibians. After the act of copulation the female lays the eggs directly into waters and places them in the tissues of water plants or in the mud.
May-flies Ephemeroptera mastered different zones of water environments, starting from sediments covering the bottom, where they bore the tunnels, to the zone of water vegetation where they live on the leaves and stems of plants. Larvae mainly eat algae and small organic parts. Perfect insects live very short - from several hours to several days. At this time they only consume the reserves accumulated during the life of larva. Their underdeveloped alimentary canal does not allow to receive the food. After the mating flight the males die while the females lay eggs directly to water or on the surface of water plants. Larvae live about one year, sometimes even longer.
Caddisflies Trichoptera are insects similar to butterflies, however their wings in the resting position are always folded like a tile on the abdomen. Adult insects eat the nectar of flowers. The female lays eggs in packs covered with the jelly-like substance directly to the water or on the plants inclining over water. The eggs' development lasts from 2 to 4 weeks. Some individuals live inland just about 8 days. Some Trichoptera larvae build cocoons woven from the silken follicle which is built around using different materials such as: fragments of reed, spruce needles, the shells of molluscs, the grains of sand etc. Larvae living without the cocoon spin the special hunting nets which are located among the water plants or on the stones. Depending on the species, they eat plants, small water animals and dead fragments of plants.
Aquatic beetles Coleoptera aquatica are a group of insects which adapted to living in the water environment in a variety of ways. The back limbs of many species were equipped with the thick natatorial stubbles. Thanks to that these insects are perfect swimmers. Adult insects, despite breathing the atmospherical air, can stay underwater for a long time. Depending on the species, cockchafers can be herbivorous or carnivorous.
The varied-wing bugs Heteroptera are a group of insects having a characteristic stinging-sucking mouth opening and the differentiated construction of wings - the frontal wings are chitinous and membrane-like while the back wings are just membrane-like. Some species of bugs settle the water surface while others live in the water depths. Larvae are similar to adult individuals however they do not have the formed wings. Heteroptera mainly eat small living and dead water organisms.
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