Darters, skimmers, chasers, golden-ringed and emperors, with their stunning colours and amazingly agile flight, dragonflies are probably one of the most thrilling groups of insects, and Devon is one of the best counties in which to see them.
Fossil records show that insects like modern dragonflies have been around for 300 million years, some of the older fossils are huge, the size of a modern crow. The largest modern species is the giant petal-tail from Australia which has a wingspan about the same as my hand span, 17cm.
Dragonflies begin life in water, eggs dipped into a pond, stuck to waterside plants, or inserted into leaves and stems by the females adept ovipositor. The eggs hatch into something that looks more like an earwig than an elegant aeronaut, a nymph or naiad form.
The name nymph might suggest something elegant and lovely but, like the adults, they are fearsome hunters. They will eat almost any other creature in the pond or river that is smaller than themselves, including tadpoles and small fish. They have a hinged jaw called a labium or mask that shoots out to grab prey and then pull it in to be eaten. This was said to be the inspiration for the terrifying monster in the film Alien.
To make them even more fearsome, the nymphs are jet propelled. They breath through gills inside the anus and they can contract the abdomen muscles to shoot a stream of water that can propel them many times their body length.
As they grow, the nymphs shed their exoskeletons, perhaps as much as six to eight times, and they live most of their lives in this state. The emperor dragonfly lives for up to two years underwater before emerging as an adult.
When it is ready to metamorphose into an adult, the nymph will climb up vegetation and sit with its head out of water adjusting to atmospheric rather than aquatic oxygen. Then it will climb clear of the water, anchor itself firmly on an upright stem, the exoskeleton will split open at the thorax and adult will drag itself out. The wings will be pumped with a liquid haemolymph to extend fully.
The newly emerged adult will sit as the exoskeleton and wings harden, and then it is off, but it will last only a few months as an adult, long enough to breed.
Adult dragonflies are awesome aviators. Their four wings can operate independently enabling them to hover, rise up, drop down, go forwards, backwards or sideways, and any combination in between. Couple this with their incredible eyesight and you have expert hunting machines.
The eyes are huge, taking up most of the head. Their vision range is almost 360 degrees, and can sense up to 300 images per second which is better than some slow motion cameras. It has been shown that they have the ability to spot prey, other flying insects such as moths, and anticipate its flight path to allow it to be in the right place for a catch. They have a hunt success rate of over 90%.
The dragonfly grasps the prey in flight and then bites off the head before flying to a feeding post where the rest of the creature can be devoured. Feeding posts often have many scattered moth and other insect wings on the ground, showing the dragonfly returns to its favourite diner.
The males establish a breeding territory and hope to attract a passing female. Mating is a complicated process with the male gripping the female’s head with a pair of claspers at the tip of his abdomen. They fly in tandem with the female arched under the male to collect a packet of sperm he has placed under his abdomen.
There are over 25 different UK dragonflies. At this time of year you are most likely to see brown hawkers, common darters with their brick red bodies, the iridescent blue emperors, and golden-ringed dragonflies.
Dragonflies are related to but different from damselflies. These too spend most of their lives as underwater nymphs, but they are much less agile in the air and, when they perch on plants, they fold their wings along the body while dragonflies usually hold them spread wide.
Aylesbeare and Harpford Commons are excellent places to see dragonflies. If breeding, they will be seen buzzing over open water, but they spend much of their time hunting along hedgerows and across fields if there is a plentiful supply of flying insects, another reason to promote wildflower meadows and pastures.
Ed Dolphin
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