Dragonflies outlived dinosaurs

THE British Trust for Ornithology’s Garden BirdWatch survey isn’t only about birds. 
Dragonflies outlived dinosaurs

Participants monitor other creatures, such as insects, as well. The results, this year, have revealed unusual emergence patterns among dragonflies. While some of these glamorous insects appeared on their usual dates this summer, others were weeks late getting airborne. Bad weather has been blamed.

Dragonflies and damselflies are among the most ancient creatures alive today. Evolving more than 350m years ago, their ancestors witnessed the arrival of the dinosaurs and survived the global catastrophe which put an end to the giant reptiles’ 140m-year reign.

Although the two are closely related, dragonflies are bigger and fatter than damselflies. They perch with their wings stretched out horizontally, whereas damselflies either fold their wings in against the body or point them upwards. More than 5,900 species of dragon and damsel fly are known to science. They are found in every continent except Antarctica. In Insects of Ireland, Stephen McCormack and Eugenie Regan say that 24 species breed here regularly and a further eight do so occasionally.

These creatures, hatching from eggs on underwater plants, spend most of their lives as nymphs. Ambush predators, the aquatic creepy-crawlies lie in wait for the larvae of midges and crustaceans, striking snake-like with extendable mouth parts when a potential victim comes within range. Having shed its skin and grown new outfits at least a dozen times, a nymph is ready to emerge as a flying insect. After months or years underwater, depending on the species and environmental conditions, it climbs up a plant stem and sheds its skin for the last time. The four huge wings inflate and aerial hunting begins. The hawks and falcons of the insect world resemble birds of prey, their long tails helping them turn and twist in the air like fighter aircraft. Huge eyes give them excellent vision.

A week after emerging, dragon and damsel flies becomes sexually mature. In the final phase of life, lasting only days or weeks, they must find partners and mate. Some species are territorial. When the male locks onto a female, grasping the back of her head, the pair are said to be ‘in tandem’. Then, she curls the tip of her abdomen to make contact with his and sperm is transferred. The pair may remain in this position, known as ‘the wheel’ or ‘the heart’, for hours. Doing so allows time for the eggs to be fertilised, reducing the risk that the male will be cuckolded. He can even remove sperm deposited in the female’s oviduct by previous mates.

The large red damselfly is common near lakes and streams throughout Ireland. None of our other damselflies is red, so this 36mm long insect is easy to identify. The nymph of this, the first species to emerge each summer, morphs into adult form and takes wing during the first three weeks of May. During the survey of 2013, it was recorded in 15% of gardens monitored in Britain. This year, however, red damselflies did not appear until June and numbers seem to have fallen; they were found in 12% of gardens.

The common blue and azure damselflies, species also common in Ireland, showed a similar reluctance to emerge; they were three weeks late taking wing this year. According to Clare Simms of the Garden BirdWatch team, bad weather in Britain during the early part of the summer upset the plans of many insects. However, species which take wing late in the year, don’t seem to have been affected; our largest flying insects, the hawkers, emerged as usual. These huge dragonflies, however, are rare visitors to gardens so this survey was not, perhaps, the ideal vehicle for monitoring them.

We don’t know whether Irish dragon and damsel flies behaved similarly but, if they did, there may be fewer of these beautiful creatures around our ponds and streams next summer.

  • Stephen McCormack and Eugenie Regan; Insects of Ireland, The Collins Press.

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