25-July Jurassic Skies: London’s Dragonfly Dynasty

Dragonflies are instantly recognised by most of us. They are large, impressive, swift and agile insects that look X-shaped as we look at them head on. We tend to notice them patrolling their habitat, looking for food, mates and rivals. The adult males tend to be brighter than the females, with both sexes living on the wing for about a month. When they land they characteristically rest with their wings outspread at ninety degrees to their bodies. Dragonflies can loosely be divided into hawkers, which hawk or patrol constantly, and darters which tend to be smaller, fatter and not quite as restless as hawkers. They prefer to dart out from favourite perches and then quickly return to them.

Damselflies, except for demoiselles, are usually smaller, slimmer and have a more delicate, fluttering flight. They usually have rounded wings, which at rest they tend to hold over their backs. To see a good range of both dragonflies and damselflies visits to Cornmill meadows, Esher Common, Richmond Park, Home Park and Barnes Wetland Centre are to be recommended. Eighteen species have been recorded from Cornmill meadows dragonfly sanctuary alone.

Dragonflies were the dominant insect when dinosaurs rules the earth. These were the so-called ‘dawn dragonflies’ which flew in the Carboniferous period three hundred million years ago. Dragonflies today are usually brightly coloured, with metallic blues and greens, often with some stripes and spotting. They also usually have clear, but occasionally amber-coloured and multi-veined wings.

Their large, compound eyes may have as many as twenty thousand facets in each eye, compared with as little as ten in some ants. This allows them to detect movement very precisely rather than produce a clear image. This could explain why males often try to mate with other males until they get close enough to realise their mistake, and then attack. After such fights with rivals, males are often seen with tattered wings or even missing legs. Their long bodies have the legs at one end, making it almost impossible for them to walk on a flat surface. Their six spiny legs can be brought together to form a ‘basket’ in which other insects are caught and trapped in mid air before they return to a perch to devour them. In the field they are generally more fascinating to watch than most other insects.

Male damselflies are often seen courting their females. Dragonflies never court, they just seize their females whilst in flight. The male banded demoiselle Agrion splendens raises his abdomen and spreads his wings if he sees a female passing by. She reacts by landing and letting him perform a fluttering dance around her before she allows him to copulate. Copulation can be quite a complicated affair. Although dragonfly males have their genital opening at the end of their abdomen, they transfer their sperm to a structure just behind their thorax before they mate. The male then lands on a female’s back, bending his abdomen over her to grasp her head with his claspers. He then lets go and this is when we see them flying in tandem, with her still gripped by the head She then loops her body to grasp the sperm behind his thorax, by which time they can look quite tangled.

Once fertilised, she goes on to lay her eggs with her suitor still attached. The way in which the eggs are laid is also quite unusual. Still in tandem, damselflies can often be seen dipping the surface of a pond. This allows the water to wash away eggs from the end of the female’s abdomen.

Or they may be seen doing the same sort of thing along any wet, muddy banks at the side of a pond. Rarer to see is the way in which some species use their saw-like ovipositors to cut open the stems of water plants so that they can lay their eggs within the stems. In the case of the emerald damselfly Lestes sponsa this is all done with the male still attached and both may be underwater for as long as thirty minutes. Probably most stunning of all is the sight of a dragonfly migration. Even in London there have been reports in the past of common darters arriving in such numbers they looked like “drifting snow” in the distance. On such occasions, they all apparently move in the same direction collectively, and more curiously seem to flow around large objects in their path.