The Study of Dragonflies and Damselflies – An Introduction
Dragonflies are amongst the most beautiful of insects.For many people they are as much part of a summer’s day as strawberries and cream or the song of a Skylark. They bring back memories of strolls along the river bank and pond clearance days. Indeed a chance encounter can lead to a lifetimes study.
Dragonflies have traditionally never been thought of as trendy but over the last ten years or so they have fast the in thing to be ‘into’. Birds and Flowers have always been the popular side of natural history with their plethora of field guides and where to watch books. For many years the only book available for any one with a hankering for the subject was Cynthia Longford’s classic long out of print book in the Warn Wayside and Woodland series, The Dragonflies of the British Isles (1937) This was followed by Corbet’s et al Dragonflies. in the new naturalist series in 1960 reprinted in 1985.
The book which opened up the world of Dragonflies to many people was Cyril Hammond’s classic, The Dragonflies of Great Britain and Ireland first printed in 1977 subsequently a revised 2nd edition by R Merritt in 1983 by Harl Books.This sparked off much latent interest and brought together a core of interested Naturalists/entomologists to form the British Dragonfly Society in 1983. Hammond’s book transformed the beasts of myth and legend into named creatures with superb drawings and information. Up until this point there were not standard names used and most enthusiasts stuck to the latin names to avoid confusion.This is often adhered to today but they are easy to pick up and should not put people off. People are often frightened that Dragonflies will bite them and even sting ( when handled some Dragonflies curl their abdomen round as if they are about to sting the hand) , finding them quite menacing. Old country names of Devil’s Darning needles and Horse Stingers perpetuate this view. It is however a false image of these glorious insects. Even when handled they will not bite, unless you offer up your finger to the dragon which will then give a nip and they do not possess a sting , crushing their insect prey with powerful jaws. Some species such as the Southern Hawker are very curious and will hover about you as if inspecting you but will not harm you.Infact it provides the opportunity to look at the Dragonfly very closely. To many folk Dragonflies are simply wonderful winged creatures yet this is only part of their life cycle. Dragonflies can be summarised into the following stages; Egg, prolarva, a series of growing larva or nymphs and the winged adults. Unlike butterflies they do not have a pupa or chrysalis stage, this is known as incomplete metamorphis. This is quite strange as the transformation from larva to the adult stage is absolutely amazing.
Mating and Egg Laying
Dragonflies belong to the order odanata ( which means toothed created by Fabricus in 1793) All the species in Northern Europe with the sole exception of the Common Winter Damselfly Sympecma fusca (not found in Britain a central European Species),have an annual cycle in which no adults overwinter. The cold period is passed as an egg or larva. It is crucial therefor that successful reproduction takes place for each species to survive. Some species can stagger larval emergence over two years which can allow survival if reproduction fails in one year.
Courtship in Dragonflies is minimal or absent.It may take place but may be too short lived or subtle to be observed. The courtship of the Agrion Damselflies is well known and documented. It is quite a hypnotic spectacle .With most Dragonflies it is a straight forward grab of the female if she is willing. She will not respond if she has already mated.
Once the Dragonflies male has grasped the female at the back of her head with his anal claspers the act of mating can take place in the air, on the ground or perched amongst vegetation. It can last a matter of seconds or up to several hours. The processes and the genital structures involved are quite unique in the insect world.
Some time before mating, often many hours before , since it may be the first thing the male performs on reaching his perch in the morning, the male dragonfly transfers his sperm from his normal genital opening near the end of the abdomen (below the 9th segment,the organ is functional but inadequate to ensure impregnation of the female) to the unique accessory genitalia situated below the second and third abdominal segments( these are copulatory organs which are not connected to the gonads) This is done by bending the tip of his abdomen around until it touches the accessory organs either in flight or when perched.The accessory organs are then ‘charged ‘ ready with sperm for direct contact with the female copulatory organs,which lie at the tip of her abdomen.These accessory genitalia consist of a sperm bladder for storage of sperm; a structure which corresponds in function to a penis;and some grasping organs which can grip the female’s copulatory organs during mating. research has recently shown that these spoon like appendages can clean out the female of sperm from previous couplings to make sure that the male mating can fertilises the eggs to be laid.
Copulation takes place after the male has grasped the female by the process of her bending her abdomen round so that the genitalia at the tip meet with his accessory genitalia below segments two and three. The pair are now attached to each other in two points and this mating position is known as the wheel or’ heart position’.In some species such as the Libellula mating takes place in the air in a matter of seconds but in most species it is more leisurely and may last for an hour or so.
Some species remain in contact for the egg laying process whilst other males separate and fly above the female keeping other males at a discrete distance.Some species scatter their eggs, some lay in floating vegetation , many of the Damselfly species submerge for up to 15 to 20 minutes.
Flight period and length of life
In Britain there are species on the wing from late April through to late November (in good years) The first species normally to emerge in large numbers is the Large Red Damselfly Pyrrhosoma nymphula. Some individual Large Reds have been known to live 47 days but 50% of individuals die within three weeks of emergence within a week of attaining sexual maturity.Some studies have shown that Emperor Dragonflies and Common Hawkers can live two to three months. It is likely that late November flying common Darters have reached this age.