Development stage of dragonfly
The life cycle of the dragonfly varies from six months to as much as six to seven years. The first stage of their life cycle is egg. You can find more about different speices of dragonflies here
Stage 1. EggEgg is the first developmental stages for drgaonfly.
As you can see in the picture on the right, female dragon flies
lay eggs in or near water. Eggs are often placed in or on plants. Dragonflies are oviparous animals. Oviparous means they lay eggs with little or no other help from their mother. Some other dragonflies are exophytic. They cannot fully function as oviparous and poorly lay their eggs directly onto the surface of the water or into mud at the water's edge. The eggs of endophytic species are long and cylindrical, while those of exophytic species are broad and ovual shaped. In the end of the egg, there is a very tiny hole through where the sperm enters just before depositing eggs. This is where the larva will later hatch which we will look in the next developmental stage.
In order to prevent the eggs to sinking into the mud or water, egg has a subtance surround it that protects it from attach to the leaves of plants or stones under the water. Most eggs start to develop as soon as they were laid. The next developmental stage, larva, hatch out one to three weeks after they had laid.
Stage 2. LarvalThe second developmental stage, larva, is the growth stage of an dragonflies. In order to grow a new larva, developing larva repeats to shed one outer casing. This phenomenon is know as molt. Periods between these moults are called 'instars' and the number of instars necessary to complete development varies between eight and fifteen. When the larva reaches the final instra, it develops all the organs it needs to sustain life as a dragonflies.
As shown in the picture (left), the larvae of dragonflies have robust bodies that are somewhat bullet-shaped.
A larva is a juvenile form of animal with indirect development. It has special organs which do not occur in the adult form. Dragonflies spend most of their life cycles in the form of larval. In this stage, they live beneath the water surface, using internal gills to breathe. This stage lasts about three months to rour or more years.
Stage 3. Emergence
When larva completes its growth and if the enviornmental condition permits, dragonflies ends its long aquatic life and begins a new life. In the third developmental stage, emergence, dragon flies live completely separte life from the water.
To meet the emergence, the larva climbs up the stem of plant until it is well out of water. It holds itself firmly and breaks at the back of the head and slowly the adult insect emerges. This process is shown on the right picture.
As soon as the adult insect emerges, 'blood' is then pumped strenuously round the body. It expands the body and also the wing-buds, transforming them into the beautiful lace-like wings which the insect will soon use to fly away from the water.
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Stage 3. Imago (Adult)
In the adult stage, dragonflies can fly. The necessary growth having been achieved during the larval stage, the imago can concentrate on ensuring the continued existence of its species: it is the stage of dispersal and reproduction.
Other Characteristics... The structure of dragonflies' eye makes a good eyesight. Their
compund eyes have 30,000 facests and they have a light-sensing organ which makes them to view 360 degrees of field vision. Their main predators are fish and frogs and main source of food is fish-spawn, tadpoles and smallers insect's larva. They are also one of the fastest insects, travelling about 97 km/hr.
Resources
Widipedia
http://en.wikipedia.org/wiki/Dragonflies-
http://en.wikipedia.org/wiki/Dragonflies-
A Beginner's Guide to Dragonflies
http://people.colgate.edu/wda/Beginners_Guide.htm
http://people.colgate.edu/wda/Beginners_Guide.htm
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