It’s been a bumper year for dragonflies and local ecologist Paul Chanin has been observing and photographing them in his garden. In this report, he explains how to tell a dragon from a damselfly and gives us a fascinating insight into the habits and lifecycle of these remarkable insects.
Our pond is only 8 sq metres in area (about 11 ft by 8 ft) but produced nearly two dozen dragonflies in June and early July. On one day, July 2nd, there were four! It takes several hours, sometimes more than a day, for the adult dragonfly to be ready to fly which gives plenty of time for photography.
Dragons and damsels
The species we have is the southern darter which has a zigzag of yellow/green patches along its body. It is nearly 70 mm long (3in) and its wingspan is 110 mm (over 4in). Like all dragonflies, when it is fully grown its wings stretch out sideways like a plane and cannot be folded across the back of the body. The similar and closely related damselflies are easily distinguished at rest because they can fold their wings. They are also much smaller, with bodies which are about half as long, while the abdomen (‘tail’) is about the thickness of a pencil lead. We see at least two species of damselflies around our pond; the small red damselfly and the southern damselfly which has a blue body.
Both dragons and damsels belong to an ancient group of insects called the Odonata which first flew across the earth during the carboniferous period more than 300 million years ago. One of the early species had a wingspan exceeding 70cm (more than 2 ft) which would have been terrifying if humans were around at the time. Today the largest ones are only a quarter that size and live in Central America.
The adult dragonflies that we normally see have a fairly short life span, only a few weeks during which time they seek out a mate and a suitable pond to lay their eggs, before dying. However, the young live much longer and have an aquatic lifestyle in a form known as a nymph. This stage can last for two or three years when the animal lives entirely underwater. The nymphs are efficient predators with large eyes and a remarkable set of jaws on a hinge structure under the head. This can swing forward to catch small animals a centimetre or more in front of them and they prey on animals up to the size of small fish. They mainly crawl around but can propel themselves forward by a form of jet propulsion when they expel water from the end of the abdomen.
Unlike butterflies, which produce an immobile cocoon or chrysalis in which the young animal changes from a maggot-like caterpillar into a fully developed adult, dragonfly nymphs change directly into adults within a few hours. The dragonfly nymph breathes water right up to the stage when it crawls up a plant stem and starts to emerge as an air breathing adult. A remarkable feat.
The late stage of a dragonfly nymph has several features characteristic of adults; large bulbous eyes and jointed legs with sharp claws on the end which enable them to grip firmly onto plants. They also have small structures on their backs which contain the wings, neatly folded and ready to enlarge on emergence as blood is pumped into the veins.
Aided by their four wings, dragonflies are remarkable fliers, capable of hovering, flying vertically upwards, backwards and even upside down. Some species can attain speeds of 55 km an hour (35 mph) - very helpful when catching prey on the wing. The wings have some remarkable design features. The distinctive veins are particularly important. They provide rigidity, especially along the leading edge, but not too much and enable the wings to be ridged rather than flat, particularly towards the front, which aids airflow. They also ensure that when bending does occur it happens in ways that maximise the efficiency of the wings.
Male dragonflies are territorial and chase other males away from a pond or patch of water they have adopted, while waiting for females to enter it. If the female is ready to mate, the mail grasps her behind the head with special claspers at the end of his abdomen. To transfer sperm, which is held in the male’s thorax (main part of the body with the legs), the female has to connect the end of her abdomen so that the two animals form a loop. After mating, the female lays her eggs in the water, sometimes in tandem, when the male continues to clasp her to make sure that no other male gets a chance to mate before the eggs are laid!
There are over 40 species of these remarkable animals in Britain, about half of which live in the southwest. If you have a pond or take a walk beside a lake or river from June to September, do keep a look out for dragons and damsels.