Dragonflies are part of the Odonata order, and Anisoptera infraorder. They are agile fliers and have a vast palette of metallic colours which makes them conspicuous in flight. They can fly straight up and down, hover like a helicopter and even mate mid-air. If they can’t fly, they’ll starve because they only eat prey they catch while flying, when in their final adult stage.
There are around 3.000 species of Ansioptera spread around the world, with most of them being located in the tropical regions, and fewer in the temperate ones.
Most of them are considered beneficial as they pray on smaller insects as adults. They are a great control on the mosquito population, as a single dragonfly can eat 30 to hundreds of mosquitoes per day. They also eat gnats, flies and other flying insects. Dragonflies have even been seen eating winged termites as they fly out of the ground. As a larva, they eat tadpoles or small fish.
They can, however, be considered pests as well, as they are predators both in their aquatic larval stage and in their adult one. Dealing with a dragonfly infestation can affect your crops, and knowing how to keep them in check is important.
Description and distribution
Dragonflies are found everywhere around the world, except for Antarctica, with tropical areas being more populated than the more temperate ones. Pantala flavescens is probably the most widespread dragonfly species in the world, occurring on all continents in the warmer regions. Depending on the area where they are found, certain species have adapted to temperatures between 18 and 45 °C, such as those living in the Mojave Desert. They can also be found at different altitude levels, from sea level to the mountains. However, their number does decrease and the diversity of species diminishes with the raising altitude. Their altitudinal limit is about 3700 m, represented by a species of Aeshna in the Pamirs.
When it comes to their description, dragonflies, no matter their type, or the place where they can be found, have a few general characteristics, and those are their slender bodies, their wings and the head fully covered in eyes. As with any other insects, the adult dragonfly has its body separated into three main segments: the head, the thorax and the abdomen.
The head is very large and has short antennae. However, it is dominated by two compound eyes, which cover most of its surface. These provide complete vision in the frontal hemisphere of the dragonfly. These compound eyes meet at the top of the head, however, besides them, the dragonflies also have three simple eyes, also known as oceli.
The mouth of the dragonfly is strong and adapted for biting, as it has a toothed jaw that assists the insect in quickly catching and devouring its prey.
The thorax consists of three segments, as in all insects and it bears the two pairs of wings and three pairs of legs of the dragonfly. The wings are narrower at the tip and wider at the base and do not fold, even when the insect has landed on the soil. They are long, veined, and membranous, with the hindwings being broader than the forewings. The legs are rarely used for walking, but are used to catch and hold prey, for perching, and for climbing on plants. The abdomen is composed of 10 segments and this is where their reproductive organs can be found.
Although in adulthood, the dragonfly looks generally the same, structure like, as a nymph, their aspect differs depending on the instar they are part of. Dragonfly nymphs are loosely classed into claspers, sprawlers, hiders, and burrowers, and they are known to be able to remain in the nymph stage for up to 2 years. The main difference from the adults is that the nymphs lack wings and reproductive organs. They do have internal gills and water is pumped in and out their abdomen through an opening at its tip, as they spend their life in water.
The coloration of a dragonfly is an interesting aspect, as they have iridescent or metallic colours, with an overall combination of yellow, red, brown, and black pigments, with structural colours, which make them be considered some of the most beautiful insects, along side butterflies. Freshly emerged adults often have a pale coloured body, and the strong colours appear only after a few days. Dragonfly nymphs are usually a well-camouflaged blend of dull brown, green, and grey.
Breeding and dietary information
The mating in dragonflies is quite a complex, choreographed process. The males need to first attract the females to their territory while driving away rival males. When they are ready to mate, the male grasps the female by the head and the pair fly in tandem with the male in front, sometimes resting on a twig or plant stem. The female then curls her abdomen and forwards under her body to pick up the sperm from the male’s secondary genitalia, while the male uses his “tail” claspers to grip the female behind the head. The fertilisation can be delayed, so the male is in danger of having his sperm removed by other males, as they insert their own.
Depending on the specie, egg laying can take place in two forms. In some families, the female has a sharp-edged ovipositor with which she slits open a stem or the leaf of a plant on or near the water, and then she pushes her eggs inside. In other families, the female lays her eggs tapping the surface of the water repeatedly with her abdomen, by shaking the eggs out of her abdomen as she flies along. After the egg is laid, the insect does not go through a pupal stage, by only through several nymphal stages, from which then the adult emerges. A dragonfly can lay up to 1500 eggs, which then take up to a week until they hatch into aquatic nymphs, which then moult between 6 and 15 times, as they grow. Most of a dragonfly’s life is spent as a nymph, under the water, as it can take up to two years until they develop into an adult. When they are ready to become adults, they exit the water surface and climb on a plant, where they then have their final moult, with the adult dragonfly emerging, swallowing air and expanding its wings.
Dragonflies are agile fliers, as they are capable of even migrating across oceans. They can move in any direction and changing direction suddenly. Their wings behave quite dynamically during flight, flexing and twisting during each beat.
Regarding their feeding habits, it is known that dragonflies are excellent for pest control. Due to their speed and flight agility, they are able to catch and carry their prey while flying. They are mostly carnivorous, as they eat a wide variety of smaller insects, such as: small midges, mosquitoes, butterflies, moths, damselflies, and smaller dragonflies. A dragonfly can consume up to a fifth of its body weight. This is why dragonflies are a good natural pest control method, especially when dealing with a mosquito infestation. They are also voracious predators in their larval state as well, eating bloodworms, other small insects, tadpoles and small fish.
Dragonflies can themselves become pray, as they are the preferred meal of birds such as the falcon, the merlin or swallows. Some wasp species also prey on the dragonflies and while in their larval stage, many ducks, herons, and frogs eat them.
The relationship between dragonflies and humans
Dragonflies have been the subject of research for a long time, especially because of their ability to fly. However, due to the massive destruction of rainforests, many species are in danger of becoming extinct. Damming rivers and drainage of low-lands is also contributing to the disappearance of suitable habitats for dragonflies. This is also why, in order to survive, many species adapt and start affecting crops. Many dragonflies now depend on rice fields, ponds and creeks and as they are attracted to shiny surfaces, such as gravestones, solar panels or automobiles, which they mistaken for the surface of water, laying their eggs can now become an issue. This also impacts the development of the dragonfly population, adding to their fast decline.
Normally, dragonflies are insect you would want around your yard, as they are not dangerous for humans, but they do help you get rid of annoying insects. However, for the very same reason, they, themselves, can be considered pests, especially to apiaries, because they also tend to feed on bees when the opportunity arises. If you do want to get rid of dragonflies, as you consider they are to numerous in your yard, you can follow the steps presented in our other articles about this specie, as the will teach you ways in which you can ‘Prevent a dragonfly infestation’ or ‘How to get rid of dragonfly infestation’ should this be the case. Follow the methods presented there, and keep in mind that when it comes to dragonflies, you might want to think twice about deterring them from your yard.