Published on February 15, 2013 by Amy
Dragonflies form an important part of Wetland wildlife and they play a significant roll in its general ecology. They are among the most beautiful and spectacular insects flying today and they are also among the most ancient of living creatures.
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The Dragonfly is also known as the Darner, Darning Needle, Devil’s Arrow and Devil’s, Darning Needle, because of the superstition that it can sew up the eyes, ears and mouth of a sleeping child. Contrary to such folklore, Dragonflies are entirely harmless to humans.
Dragonflies are worldwide in distribution with more than 5,000 described species. There are about 450 species of dragonflies in North America. Dragonfly adults are medium to large insects. In fact, a fossilized dragonfly from 250 million years ago has a wingspan of 28 inches. Fortunately, present-day dragonflies are considerably smaller. Dragonfly adults are often brightly colored and have a long slender abdomen. They also have two pair of long, slender wings with many net-like veins. The wings do not fold and are held outstretched when at rest. Adults are usually found near water but are good fliers and may range several miles. They are active during the day, and can be observed hunting and mating. Males of some species are territorial, defending their domain from other males who enter.
Odonate larvae are non-discriminate hunters which will eat any animal as large as or smaller than themselves, including their own species. Small vertebrates such as tadpoles and fish fry are not immune from attack. Prey may be stalked or ambushed. The labium is shot out by a rapid rise in haemolymph pressure. The prey is held with the hand-like palps and is withdrawn to be chewed by strong mandibles.
Almost all odonate larvae are aquatic. They occur in every sort of water body from soaks and seepages to streams and rivers, lakes, temporary pools and water-filled tree holes. A few species tolerate moderately salinity, a few others have semi-terrestrial larvae which roam across the surface of bogs and swamps at night. A half-dozen or so fully terrestrial larvae are known from distantly related families.
As they grow, larvae undergo approximately 10-20 molts, over a time between 3 months and about 6-10 years depending on species. Instar number is not always fixed but may depend on seasonal conditions and food supply. Wing pads develop externally from about the 6-7th instar. Metamorphosis is direct without a pupal stage and emergence takes place on a fixed support out of the water, sometimes a considerable distance from the water”s edge. The newly emerged adult flies away from water for a few days to feed and mature, during which time the full adult color develops. Teneral (new) adults can be recognised by a glassy sheen of the wings. Additional color changes occur later in life in some species.
Adult Odonata are visually oriented hunters with exceptional aerobatic ability and extremely acute eyesight. Many are strong fliers, and to catch them can be extremely difficult. Males tend to congregate around the breeding sites where they may be seen either perched on waterside vegetation, hovering over small territories or hawking up and down in search of females. Females of many species spend much time away from the water, only appearing to mate and lay eggs, but some congregate with the males. Most adults are long-lived. In cold climates some over-winter in sheltered places and in the dry tropics some aestivate through the dry season. Some undertake long dispersal flights, including transoceanic journeys, but others remain tightly associated with their larval habitat.