Dragonflies and Damselflies
The order Odonata ("toothed ones") includes some of the most ancient and beautiful insects that ever roamed Earth, as well as some of the largest flying invertebrates ever to have lived. Odonata consists of three groups: Anisoptera (which includes dragonflies), Zygoptera (which includes damselflies), and Anisozygoptera (a relict group represented by only two living species. This order is very diverse with about 5000 species, and its members are easy to observe.
Both dragonflies and damselflies belong to the Odonata, which is a subgroup of insects, which in turn is a group of uniramian arthropods. Many characteristics distinguish Odonata from other groups of insects -- minute antennae, extremely large eyes (filling most of the head), two pairs of transparent membranous wings with many small veins, a long slender abdomen, an aquatic larval stage (nymph) with posterior tracheal gills, and a prehensile labium (extendible jaws underneath the head). Among living Odonata, there are twenty-five families, mostly dragonflies and damselflies. Of all their characteristics, the easiest way to tell a dragonfly or damselfly from other insects is by the size of the eyes and shape of the abdomen. If the eyes are very large in proportion to the head and the abdomen is long and thin, then it is almost sure to be in Odonata.
A dragonfly is an insect belonging to the order Odonata, the suborder Epiprocta or, in the strict sense, the infraorder Anisoptera (from Greek ανισος anisos, "uneven" + πτερος pteros, "wings", due the hindwing being broader than the forewing[1]). It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body. Dragonflies are similar to damselflies, but the adults can be differentiated by the fact that the wings of most dragonflies are held away from, and perpendicular to, the body when at rest. Dragonflies possess six legs (like any other insect), but most of them cannot walk well. Dragonflies are some of the fastest insects in the world.
Dragonflies are valuable predators that eat mosquitoes, and other small insects like flies, bees, ants, wasps, and very rarely butterflies. They are usually found around marshes, lakes, ponds, streams, and wetlands because their larvae, known as "nymphs", are aquatic beings.
What's an Odonate?
Dragonflies and damselflies together make up the insect order Odonata. The Greek word "odon" means tooth, and the name here refers to the toothed jaws of these predatory insects. Fortunately for us, dragonflies and damselflies use their formidable mandibles on mosquitoes, midges, and other pest insects.
- Of its ability to seek out pure water
- Of its ability to Reflect multiple colors with changing angles of light
- Of its awe inspiring flight and speed
- Of its ability to almost single handedly control insect populations
- Of its ability to adapt to change with indescribable ease
- Of the way it lives out its adult life, living each moment to the fullest
Compound Eyes
Like all arthropods, dragonflies have compound eyes - only, they are a little more specialized, suited for a born predator.
When dragonflies see, they don’t exactly see…they more sense. Sense movement at a much wider angle than any human could even imagine. The reason being, its eyes are ball-like and see at a complete 360 degree span. Each Ommatidia, called Ommatidium in singular, is an eye in itself, capable of seeing anything right in front of it. This helps the dragonfly sense movement anywhere around it.
Furthermore, the dragonfly has a flattened area right in front of its eyes with a concentration of eye cells that see directly in front. This helps it see the little mosquito as it flies around, so it can home in on its meal. Other predators of the Arthropod family like the Praying Mantis and the best fliers like bees have similar flattened fronts to help them see better, as they fly.
The body of the dragonfly is supported by two pairs of extremely powerful wings that help it float at the slightest breeze and can flap fast and hard enough to hover even against a strong head wind. Here again, although its wings are transparent and seem quite frail, you’ll find they’re a whole lot stronger than they might seem at first sight. The construction of my wings and the fact that they are not jointed like those of butterflies, and can operate independently, helps the dragonfly fly and run a neat little air show on its own, capable of flight in all directions, up, down, left, right, forwards and even backwards. Nope, the hummingbird is not the only one that can go on the reverse gear.
The surfaces of dragonfly’s wings are not smooth. They have small pocket like ridges that catch even the slightest gust of wind to take flight. Although the rough surface poses a certain degree of aerodynamic drag, the dragonfly can move fast enough, and more importantly, have enough control in flight to make sure if it catches sight of its meal, it’s as good as eaten. Not many an insect escape its six legs once the chase begins, as it out-flies the prey and grabs it using its legs to eat them at ease. To make it as simple as possible, the legs are positioned in such a way that they form a pouch like shape. This helps grab prey leaving them with very little chance of an escape.
As the dragonfly flies a lot, it needs to both heat up and cool off and hence, the famous Obelisk pose. The muscles that flap its wings need to be warm at all times.
Coming back to the Obelisk, dragonflies bask in the sun as much as possible when they need the heat. And when they need a little breather from the warmth, they position their bodies in such a way that it makes little or no direct contact with the sun’s rays.
They also do something quite similar to catch the warmth of the setting sun. Same pose, vastly different purposes.
This is about the biology of the beautiful dragonfly. If you want to know more about the lifecycle of the dragonfly, what it eats or what the dragonfly symbolizes, check out the pages dedicated to each.
The Nymph Stage
Once the dragonfly eggs hatch, the life cycle of a dragonfly larva begins as a nymph. A nymph looks like a little alien creature. It hasn’t grown its wings yet and has what looks like a crusty hump hanging onto its back. Dragonfly nymphs live in the water while they grow and develop into dragonflies. This portion of the dragonfly life cycle can take up to four years to complete, and if the nymph cycle is completed in the beginning of the wintertime, it will remain in the water until spring when it is warm enough to come out.
Dragonfly nymphs live in ponds or marshy areas because the waters are calmer than in a stream or river. Sometimes they can be found in the calmer backwaters of rivers, too. Dragonfly nymphs may eat smaller dragonfly nymphs as they develop.
The Adult Dragonfly Stage
Once the nymph is fully grown, and the weather is right, it will complete the metamorphosis into a dragonfly by crawling out of the water up the stem of a plant. The nymph will shed its skin onto the stem of the plant and will then be a young dragonfly. The skin that the nymph left behind is called the exuvia and you can find the exuvia still stuck to the stem for a long time after the dragonfly has left it.
Once the dragonfly leaves the exuvia it is a full grown dragonfly. The dragonfly will hunt for food and begin to look for a mate. Once the dragonfly finds a mate, the female will find a body of calm water that will be a good place to lay her eggs, and the life cycle of the dragonfly begins all over again. Adult dragonflies only live about two months. 
How do they grow?
Dragonflies hatch from eggs in freshwater, and spent at least a few months (sometimes several years) as aquatic predators. As they grow they molt (shed their whole skin at once) many times. Once they are big enough, they crawl out of the water and the adult stage emerges from the skin of the nymph. Once they have transformed into the winged adult stage, the stop growing.
Most dragonfly species spend the winter as nymphs in the water, but some migrate south, and spend the winter as adults. In few species that lay their eggs in the late summer or fall, the eggs don't hatch until spring. Dragonflies emerge from the water in the warm months of spring or summer.
How long do they live?
Dragonflies live for months at least, and some live for several years as aquatic larvae before emerging and living for a few months as adults.
What do they eat?
Dragonflies in their aquatic stage eat many kinds of small animals: aquatic insects, tadpoles, small fish, and other invertebrates. Adult dragonflies eat flying insects, especially mosquitoes and other true flies, but also aphids, smaller dragonflies, damselflies, and just about any other insects they can grab.
What eats them and how do they avoid being eaten?
Immature dragonflies avoid predators by hiding, and by jetting away if they have to. Adult dragonflies avoid predators with their quick and agile flight, and hide in vegetation when it is too cold to fly.Known predators
- ¦frogs
- ¦fish
- ¦large spiders
- ¦insect-eating birds
What roles do they have in the ecosystem?
Dragonflies are sometimes the top predators in ponds with no fish. Adult dragonflies help control populations of mosquitos and other flies.
Immature dragonflies avoid predators by hiding, and by jetting away if they have to. Adult dragonflies avoid predators with their quick and agile flight, and hide in vegetation when it is too cold to fly.
No comments:
Post a Comment