Dragonflies

Kruger National Park | June 2017

Just below Lebombo Camp the road crosses the N’wanetsi River at the weir. It is a beautiful place, with golden-yellow fever trees growing on the banks of the river and hippos that stare at you with tiny eyes that just stick above the water surface, as you park your vehicle and look at the scene. The rooms hug the side of the ridge like eagle nests, overlooking the river below. This is a great place for birding, with kingfishers, herons, crakes all doing their daily activities. As you sit and watch the river-life you may notice the glistening wings and bright colours of the dragonflies as they hunt down their prey and protect their territories. This is a great place to look for these beautiful creatures. Flashes of blue and red and violet. They seem to be almost always busy, darting this way and that, hovering, chasing or just perching watching everything that moves near the water, their wings scattering the sunlight in sparkles.

Dragonflies and their relatives are an ancient group of creatures. There are fossils of dragonfly-like animals from the Upper Carboniferous Period (325 million years ago i.e. before the dinosaurs) that included the largest insect that ever lived, Meganeuropsis permiana with a wingspan around 750 mm (30 in). Dragonflies are insects that fall into the Order Odonata.

Dragonflies are found on every continent except Antarctica. They can be found from sea level and all the way to the tops of mountains (decreasing in species diversity with an increase in altitude). A number of dragonfly species are known to migrate. The globe skimmer or pantala was recently documented to travel all the way from India to Africa and back again (a round trip of between 14 000 and 18 000 kilometres). This dragonfly has an almost worldwide distribution.

Dragonflies can sometimes be confused with damselflies (which also fall into the Order Odonata). Damselflies are similar in structure, though they are usually lighter in build than Dragonflies. Damselflies tend to hold their wings folded, at rest, along or above the abdomen, whereas the wings of most dragonflies are held flat and away from the body. Dragonflies are strong and agile fliers, while damselflies have a weaker, more fluttering flight. It is also fairly easy to tell dragonflies from damselflies by looking at their eyes. The eyes of damselflies tend to be spread apart, whereas the eyes of dragonflies are almost joined and wrap around the head like a motorcycle helmet (or perhaps more like the helmet worn by jet –fighter pilots).

Dragonflies are extremely interesting creatures, both in design and behaviour. Consider their anatomy: The amazing structure of their strong, yet filamentous wings, which are attached to the back of the thorax and controlled by individually separate muscles, allows them to hover, change direction instantaneously or even reputedly fly at speeds of up to 60 kilometres per hour. This is important, as dragonflies are considered to be some of the most voracious predators in the insect world. Adult dragonflies often perch on overhanging reeds or on rocks searching for potential prey. Dragonflies usually go for small flies or mosquitoes, although they will also eat butterflies and even smaller dragonflies, if they can catch them (in fact they will pretty much eat any other flying insect that they can overpower). When they do see prey they tend to give chase in aerial pursuit. They out-pace and out-manoeuvre their prey. When they intercept their prey they first grip hold of it in their front legs, which are curved up and cage the prey, cutting off its escape route. The dragonfly then bites off the wings of its prey, immobilizing it. It can then return to a perch to feed or just consume its food mid-air without even bothering to land.

Dragonflies go through incomplete metamorphosis (they are hemimetabolous). This means that after hatching the nymphs go through various moults until they become adults (as opposed to having four distinct growth stages). Dragonfly larvae, or nymphs, live underwater (in ponds, rivers etc.) and scoot through the water by shooting a jet of water out their rectum, like tiny torpedoes. Even in their larval stages dragonflies are efficient hunters and predators.

Dragonfly nymphs are even more “cold-blooded” than their adult counterparts when it comes to killing. During their waterborne life, they hunt small insects and other larvae that are in the water with them (especially mosquito larvae). Some dragonfly nymphs will even eat tadpoles and small fish. To capture and hold their prey the nymphs have a specially designed mouthpart, where the lower lip of the mouth (the labium) has been modified into a hinged, extendable arm with a scoop at the end called a mask. Normally this mask is folded back and held flat against the face, but when potential prey is seen swimming or drifting past, the mask is rapidly shot forward to seize the prey.

Dragonflies have some of the most amazing eyes in nature. Their eyes literally surround most of the head of the adult dragonfly. They have an incredibly advanced sense of vision. They can see all around them. Many insects, house flies for example, have compound eyes with about 6 000 eye facets that give them a panoramic view of their surroundings. Dragonflies, in comparison, can have up to 30 000 facets / ommatidia. Each facet creates its own image, and the dragonfly brain compiles those thousands of images into one picture. This enables them to see movement extremely well. This is the reason it is very difficult to sneak up on a dragonfly.

Another amazing thing about dragonfly eyes is that, as humans we have what’s known as tri-chromatic vision, which means we see colours as a combination of red, blue and green. This is thanks to three different types of light-sensitive proteins in our eyes, called opsins. A study on dragonflies has shown certain species can have up to 30 different visual opsins! Dragonflies can supposedly see ultraviolet on top of blue, green and red. And it is thought that they can recognise polarised light coming off reflective surfaces like water as well.

As we watch the dragonflies watching us and everything else that moves around them we might see them guarding their little patch of river. Most of the dragonflies at the pools of water are males. They are beautifully coloured, like bright jewels. Females are usually drabber and often frequent areas away from the males to avoid being sexually harassed, and only come to the water when they are ready to mate and lay eggs. The males are extremely territorial and will chase any other male, and often other flying insects away. This may result in some spectacular flying, with aerial dogfights and high-speed acrobatics. When a female does come into the male’s territory he energetically chases her and grips her behind her head with his claspers. She may then bend her abdomen to the secondary genitalia of the male to take up the sperm that he recently placed there. This position is known as the “heart” or the “wheel”. The male and female then often fly “in tandem”, low over the water while she deposits the eggs just under the water surface. In some species the male may not still be connected to the female but he may fly above her or nearby in order to guard her and ensure that rival males are prevented from removing his sperm before “his” fertilized eggs are laid, and inserting their own.

Dragonflies are important insects as they are predators, and therefore fairly high up on the Trophic Pyramid and the food-chain. They therefore fill an important function in the ecosystem (they feed on numerous other insects and keep those numbers in check). They are also creatures that require good, clean, fresh water to live in during their larval stage. As such they can be used as very important indicator species of habitat destruction and pollution levels in freshwater habitats. A drop in numbers of dragonflies or a drop in the numbers of species of dragonflies in an area could give an ecologist an early warning of habitat degradation or other issues regarding the rivers and water-bodies.

Images: Blue basker, Pantala dragonfly, Dragonfly – Red-veined dropwing, Damselfly – common citril, Violet dropwing, Orange-winged dropwing, A blue skimmer, Ferruginous gliders flying “in tandem”, and a Portia widow.