Dragonflies and Damselflies

Published in Nature Watch

These delicate-looking, exquisite creatures play an important part in the natural chain. They are especially useful to humans because of their voracious appetite for mosquitoes and other biting insects such as midges.

Emperor Dragonfly Emperor Dragonfly Photo: Steve Jones

While they feast greedily on their preferred prey, dragonflies and damselflies are totally harmless to humans. They are relatively large insects, even today, although nowhere near as large as those which lived millions of years ago, judging by their ancient fossil ancestors which have been found, for instance, in France, the United Kingdom and the United States. They have been on earth from extremely ancient times, estimated at over 250 - 300 million years. They are classified in the order Odonata, which means 'the toothed ones' and is a sub-group of insects, which in turn are classified as a group within uniramian arthropods. The Odonata order consists of about 5600 species, with 130 in Europe, and some 165 in the Mediterranean Basin. The order is divided into three groups: Anisoptera (dragonflies), Zygoptera (damselflies), and Anisozygoptera, a relict group which consists of only two surviving species. Dragonflies and damselflies belong to the hexapoda (six-legged) subphylum of the phylum arthropodia, together with all other flying and non-flying insects. (A phylum is a group which is not as high as a kingdom, but higher than a class).

Scarlet Darter Dragonfly. Photo: Steve Jones
Scarlet Darter Dragonfly, female. Photo: Steve Jones

Our Dol nature-watcher Steve Jones reported in July 2019: "Birding has been quiet, although, saying that, more has been happening than last year, as pond levels are higher. I picked up a few new species for the year, but none that are new to me on Hvar. I have seen more dragonflies and damselflies than ever before, particularly at the moment. For the previous four years the natural pool pictured below has been completely empty at this time (26.07.19). Clearly the heavy rains in May have contributed enormously to the dragonfly activity this year. That said, I am not seeing that many species but considerably more than in previous years, for instance three species of damselfly as against one previously". This was good news, as the presence of dragonflies and damselflies most often means that the ecosystem is of good quality. Damselflies are much less sensitive to pollution than dragonflies, and some species of Odonata tolerate a variety of environmental conditions, so they can thrive in a wide range of habitats. Those which don't tend to be found in specific locations, whether flowing streams or rivers, still pond-water or marshy land.

Full waters: first time in four years. Photo: Steve Jones

Heavy spring rains on Hvar tend to create moving streams in the otherwise dry water-courses, so this may have accounted for the increase in species that Steve saw in 2019.

Red-veined Darter Dragonfly. Photo: Steve Jones

Dragonflies and damselflies are especially well equipped to devour other insects from their earliest moments. Their larvae (nymphs) develop from eggs which are laid in aquatic plants or moss, or on a water surface such as a pond or lake. They have fearsome jaws for consuming their prey, but their special weapon is an extensible, enlarged lower lip (technically labium), which is folded away and hidden under the head when it is not in use, but shoots out at great speed when a suitable victim appears within reach. The labium has a pair of hooks for capturing its prey in a pincer movement and drawing it into its jaws for consumption. This method of hunting using subterfuge is known as a mask, and the mechanism is said to be unique to dragonflies and damselflies. The insects, tadpoles and small fish which form their diet probably view the larvae in the same way as humans view the great white shark.

Blue-tailed Damselflies mating. Photo: Steve Jones

There are differences between dragonflies and damselflies, even though they look similar, and many people talk and write about them under the general heading of 'dragonflies' without distinguishing between the two. For a start, dragonfly eggs are round and measure about 0.5 mm, while damselfly eggs are cylindrical and measure about 1 mm. Some damselflies and dragonflies lay their eggs in the stems of water plants, some skim over water repeatedly dipping the tip of their body as they push out their eggs, which are washed down into the water, while some dragonflies push their eggs into sand or gravel at the edges of streams.

Emperor Dragonfly laying her eggs. Photo: Steve Jones

The larvae (nymphs) vary in shape according to their habitat, and may be just over 6 mm to some 6 cm in length according to species. In general, the dragonfly larva is shorter and fatter than that of the damselfly. Its gills are inside its abdomen, and it breathes by drawing water into the rectum and then expelling it. For propulsion, the abdomen can contract and expand forcefully, squeezing water through to create the power for short bursts of rapid movement. In the damselfly larva, three gills shaped like fins are attached to the tip of the abdomen, which is longer and narrower than the dragonfly's. Unless eaten by predatory fish, the larvae remain in their habitat for an extended period of about two years for most European species, up to about six years. During this time, they moult between six and fifteen times.

Emerging Vagrant Emperor Dragonfly. Photo: Steve Jones

To shed its outer casing for the last time the larva comes out of the water on to a rock or plant stem, in order to emerge as an adult with functioning wings. It misses out on the intermediate stage between immaturity and adulthood which other insects have, such as butterflies and beetles. Adult dragonflies and damselflies are not as diverse in form as their larvae. Unlike their larvae, they have few natural enemies, one being the hobby, a small bird of prey, although in their first few days as adults they are vulnerable to other predating birds and insects until their bodies harden and they begin to fly at speed. They are equipped with extremely large eyes which have some 28,000 units called ommatidia, and apparently use about 80% of their brain-power processing visual information from all directions: they can detect movement at a distance of 12 metres (40 feet). By contrast, their relatively large heads have only small antennae, but they retain the large extensible labium for grabbing their food.

Scarlet Darter and Blue Skimmer Dragonflies on sedge. Photo: Steve Jones

Their six legs serve mainly for catching prey or perching, rather than walking. They have various methods of controlling body temperature according to species and habitat, including basking in the sun and using their wings. They have two pairs of wings, which include a specialized hinge-type structure called a nodus on their front edge, whose purpose is to allow the wing to deform during flight without breaking. This is only one of many specialized features which allow the wings to work in highly complex ways.

Broad-bodied Chaser Dragonfly. Photo: Steve Jones

There are various differences between adult dragonflies and damselflies: the latter have smaller eyes, separated by a distinct gap, and more slender bodies than dragonflies. The main difference is in the wings: the dragonfly's hind wings are larger than the front ones, and broader at their base, whereas damselfly wings are the same size and shape, and tapered where they join the body. This means that the damselfly cannot fly as fast as the dragonfly. At rest, the damselfly folds its wings up across its back, whereas the dragonfly holds its wings straight out sideways. Dragonflies can attain high speeds and highly complex manoeuvres in the air. Some species are migratory, and have been tracked covering up to 18,000 km in the round trip between India and South Africa.

Southern Emerald Damselfly. Photo: Steve Jones

Just as they are fearsome predators, dragonflies guard their mating-ground territories ferociously. Some damselflies are also territorial, whereas others simply search for their mate by flying around and exploring. When mating, a dragonfly generally doesn't waste time on any kind of genteel courtship. He simply latches on to the female by grabbing the back of her neck, after which the two adjust position to form a kind of heart-shaped wheel so that the male can penetrate the female and transfer his sperm to her. In some cases, the male removes any sperm left by a competitor before depositing his own.

Black-tailed Skimmer Dragonflies mating. Photo: Steve Jones

Damselflies also form a wheel while mating, as in the photograph of the blue-tailed damselflies above, but are more varied in their methods of finding a mate than damselflies. Copulation may be brief or extended, and in some cases the male stays attached to the female and they fly around together right up to the moment that the female lays her eggs.

Green-eyed Hawker Dragonfly. Photo: Steve Jones

Some species of dragonfly and damselfly are under threat. Their decline is a great loss to our environment. We can only hope that gardeners, farmers and local authorities put an end to the massive use of insecticides, both larvicides and adulticides, along with the other damaging pesticides which currently blight the 'civilized' world. Poisons are counter-productive. They cause enormous collateral damage, without any positive effect. On Hvar, the damage to the insect and wildlife populations is increasingly visible, and human health is being eroded. The need to abandon chemical pesticides altogether is urgent.

Text © Vivian Grisogono MA(Oxon) 2019

Photographs © Steve Jones 2019

Many thanks to Dave Smallshire who helped Steve identify those insects which he was not sure of. Dave is co-author with Andy Swash of the highly praised guide "Britain's Dragonflies. A Field Guide to the Damselflies and Dragonflies of Britain and Ireland" 2018 (4th edition). Pub. WILDGuides. ISBN 9780691181417 (USA: https://press.princeton.edu/titles/13214.html)

Southern Hawker Dragonfly. Photo: Steve Jones
Sources:
Gullan, P.J., Cranston, P.S. 2005 (3rd edition) The Insects: An Outline of Entomology. Blackwell Publishing. ISBN: 978-1-4051-1113-3
Burton M., Burton R. 2002 (5th edition) The Encyclopaedia of Insects and Invertebrates. Silverdale Books, Leicester. ISBN 1-85605-708-9
Sverdrup-Thygeson. 2018. Extraordinary Insects. Weird. Wonderful. Indispensable. The ones who run our world. English edition 2019, pub. Mudlark - HarperCollins. ISBN: 978-0-00-831635-8.
Tennesen, K.J. 2009. Odonata: Dragonflies and Damselflies. In: Resh, V.H., Cardé, R.T. Eds. 2009 (2nd edition). Encyclopedia of Insects, Chapter 185 pp 721-729. Academic Press. ISBN: 978-0-12-374144-8.
Jongerius, S.R., Lentinck, D. 2010. Structural Analysis of a Dragonfly Wing. Experimental Mechanics 50 (9) 1323-1334.
Rajabi, H. Ghoroubi, N., Stamm, K., Appel, E., Gorb, S.N. 2017. Dragonfly wing nodus: A one-way hinge contributing to the asymmetric wing deformation. Acta Biomateralia 60 - 330-338
UCMP Berkeley Edu. Introduction to the Odonata, Dragonflies and Damselflies. (Internet resource)
Sheikh, E.M., Douglas, M. 2012. Biodiversity, Phenology, and Thermoregulatory Strategies of Odonates at Pierce Cedar Creek Institute. Undergraduate Research Grants for the Environment Report, Grand Rapids Community College.
Bumblebee. org: Hexapoda 5 (Insects) https://www.bumblebee.org/invertebrates/Hexapoda5.htm. (Internet resource)
Castro, J., 2014. Animal Sex: How Dragonflies Do It. LiveScience. (Internet resource)
Riservato, E., Boudot, J-P., Ferreira, S., Jović, M., Kalkman, V.J., Schneider, W., Samraoul, B., Cuttelod, A. 2009. The Status and Distribution of Dragonflies in the Mediterranean Basin. IUCN, Gland, Switzerland and Malaga, Spain. ISBN: 978-2-8317-1161-4
Mellal, M.K., Zebsa, R., Bensouilah, M., Houhamdi, M. 2018. Aspects of the emergence ecology of the regionally endangered Coenagrion mercuriale (Odonata: Coenagrionidae) in Northeast Algeria. Zoology and Ecology 28 (3) 224 - 230.
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