Dragonflies – Raptors of the Insect World
Dragonflies belong to an insect order Odonata which literally means “toothed jaw”. They are ancient insect that have existed on earth for 300 millions years.
Like all insects, the body of a dragonfly consists of the head, thorax and abdomen. The head is dominated by the enormous compound eyes. In contrast, the antenna is minute that it is not noticeable. Attached to the thorax are three pair of legs, and two pairs of membranous wings that move independently. Dragonflies can hover, accelerate forward and fly backward to some extent. The abdomen is distinctively long, and on its surface are numerous spiracles - tiny openings that allow gas exchange during breathing.
Unlike insects such as butterflies that go through complete metamorphosis, a dragonfly life cycle is known as incomplete metamorphosis. It is missing the pupal stage and therefore consists of only three stages: eggs, larva (nymph) and adult.
- Eggs - The female lay its eggs into water, or lay them in emergent vegetation. In some species, the female will submerge under water to lay eggs.
- Larva - The larva, known as nymph looks somewhat like adult with pairs of three legs, but it is wingless and the body is not colourful. It will stay in the aquatic environment for up to four years, depending on species, using its internal gills to breath underwater.
- Adult - When the nymph is ready, it will climb out of water to nearby vegetation and shed their nymphal skins. Then, adult dragonfly will emerge and lives for only about a few weeks or months.
Dragonflies are often regarded as raptors of the insect world because they prey on other insects like flies, mosquitoes and midges. They have specialized organs that are useful to detect, catch and eat their prey.
Their large compound eyes consist of thousands of subunits are very sensitive to movements. The head can be tilted in many directions and therefore they have broad field of view to search for prey. Using their strong and flexible wings, dragonflies can easily out-fly their prey. They snatch their prey in mid-air using their legs and then consume it using its chewing mouthparts. Even the nymph is a ferocious predator. It preys on animals such as tadpoles and small fish using its extendable jaw.
Dragonflies may be a predator among insects, but they are not among the top organisms of the food chain. Many vertebrate like birds and frogs eat them regularly. Bee-eaters, for example, could sally forth to catch a flying dragonfly using their long bill.
Dragonflies and Damselflies
Damselflies are another insect of the order Odonata and look very much like dragonflies. Both insects have large pair of eyes, two pairs of wings and long abdomen. Additionally, damselflies share the same type of habitat as dragonflies such as streams, ponds and lakes. On closer inspection, however, there are several differences between both Odonates and some are listed in the following table.
Wings held horizontally at rest
Wings held upright at rest
Eyes touch or almost touch
Larger distance between eyes
Hind wings broader than fore wings
Both pair of wings are similar
Benefits to Humans
Dragonflies prey on insects that are considered harmful to humans especially mosquitoes. A study has shown that larvae of a particular dragonfly feed readily on larvae and pupa of the mosquito Aedes aegypti which causes dengue fever. Since dragonflies larvae require clean water to survive, its population status is also use as biological indicator in wetlands.