By Alfred Lord Tennyson
Today I saw the dragon-fly
Come from the wells where he did lie.
An inner impulse rent the veil
Of his old husk: from head to tail
Came out clear plates of sapphire mail.
He dried his wings: like gauze they grew;
Thro’ crofts and pastures wet with dew
A living flash of light he flew.
There is no mistaking the paper buzz herd from a passing dragonfly. Wings that carry one of natures most formidable, and in my option one of the most beautiful, areal predators.
I am crouching in Bennett’s water garden, one of a number of surprising oasis found in the town of Weymouth. The warm June sun rises the plants from the May downpours and the air is thronging with the sounds of long-tailed tits, black birds and traffic someway off away from this world. Occasional plops are heard as fish gasp at the surface, and I find that each pond contains fish of an ever increasing size from small common Rudd to large carp any trophy fisher would be proud to own. The main stars of these gardens are the lilies, for that indeed was the original purpose of these ponds. Started in 1959 the Bennett Family purchased the land and built over time a series of ponds for the aquaculture of lilies. Many of the original plants came from the same nursery in France that supplied Claude Monet for his garden in Giverny. The business grew and became a huge supplier of lillies for the UK and western Europe. Times have changed and the business needed to diversify and in 1999 the Monet Bridge was erected, commemorating 100 years since Claude Monet’s famous painting ‘Water Lily pond 1899’ was produced. Thought the garden still sells lilies the ponds have been made a garden and for the most part quite a pleasant one. Should you be hot on your horticulture, you may find other than the lilies, some beautiful bearded iris and ornate horsetails that this garden lacks a little diversity. However in a way this is quite nice, many gardens will stick to a strict historic style of box plants and aromatics, or go all out in exotics and rarities. In a way the planting, like the nature of the garden, is simple and in general local, remaining true to the feel Monet might have got from his garden.
I digress from the main attraction, or at least the title of this article which drew you to click it in the first place.
The basic design of the order Odonata (“toothed ones”) to which dragonflies and damselflies belong has remained unchanged for millions of years. Consisting in the main of a long abdomen with terminal appendages, a shorter thorax, minute antennae, a head with compound eyes, six legs, four membranous wings with veins, a prehensile labium (jaws) and an aquatic larval stage (nymph) with posterior tracheal gills. Their preferred habitat of waterside locations, means that they have often be in the right place to be preserved in the fossil record.
Above is the fossil of Protolindenia wittei, a dragonfly with a wingspan of about 45.5-52.5 mm. Hailing from the upper Jurassic period dates this to around 153-155 m.a. This specimen is from the Solnhofen limestone, Germany. The oldest dragonfly like fossil thus found was in Pennsylvanian sediments in Europe formed about 325 m.a , having a wingspan of 75 centimeters (Berkeley 2003). The genus is called Meganeura, with M. monyi being the so far know largest species! Living around 300 m.a the atmosphere had around 30 times the oxygen in the atmosphere as it does today, likely allowing the development of such large insects as well as a violent weather system, with regular storms. It seems appropriate that such a fearsome insect should be born from such a time. These insects were in the order Paleodictyoptera, which is the oldest group of winged insects, found in the Carboniferous period and are the forerunners for Odonata (Tait 2006). Today the atmosphere contains less oxygen and larger animals that are happy to eat the dragonfly in a moment, yet still it survives, dancing on the water with enamel beauty. one must then ask the question –
‘How has it survived?’
Most of it’s life is spent underwater in the form of a nymph. Nymphs will hatch from the tubular eggs and will undergo six-fifteen ‘molts’, with the inter-periods knows as instars, in two- six years depending on species and geographical location. The nymphs eat a varied (carnivorous) diet i.e. they are generalists, consuming what is in most abundance. This includes; tadpoles, fresh water daphina, small water beetles, occasional fish and even other nymphs, very occasionally breaking the surface for prey close to the waters edge. They follow one of the oldest rules of nature, ‘if it’s smaller than you, it’s fair game’.
Not being fussy about what you eat is one of the key factors to many of the longest surviving genera’s. Specialising in eating only one or very few things means that you are able to dominate and completely fill a niche in the environment. Panda’s for example, who’s home is dominated by bamboo have evolved this highly specialized bamboo diet to completely fill this niche and thrive with relative ease. Specialisation like this though is double edged, while it can lead to high abundance when the food supply is good, when supply is bad then populations can collapse. This has been seen time and time again in the fossil record, with species adapting to one food source and dominating the environment, but then change, such as environmental change, has wiped out the food source and the species depending on it for good.
Should a nymph then survive to its adult stage, the nymph will start to climb up, usually on a reed, were it will undergo it’s final molt into an adult. There is no inter-stage between nymph and adult, unlike in butterflies were the caterpillar will stay as a chyrysalis for a number of days before emerging. Because of this Odanata are classed as hemimetabolous, “incomplete” or “gradual” metamorphosis (Berkeley 2003). Adult dragonflys can eat food equal to its own weight in about 30 minutes, imagine eating your body weight in half an hour! (dragonfly-site). Similar to the nymph, the adults are generalists, diets consist mainly of insects. Often hunting in groups where other swarming of insects such as flies, mayflies, gnats or ants are gathering. Dragonflies will occasionally take on other aerial predators such as wasps. So complex are the dynamic of capturing a moving object in mid air, that it leads to the conclusion that Odanata posses complex nervous systems. It also means that the dragonfly must be able to calculate three things (Handley 2013);
- The distance of the prey
- The direction it is moving in
- The speed at which the prey is moving
Our results imply that the control of the prey-interception flight must include a neural pathway that takes head position into account. (Olberg et al 2007)
This means they fly to the point to which they will intercept the prey. This ability is helped by two major factors.
The first is that of their eye sight, dragonflies have 30,000 individual lenses, each facet, or ommatidia, creates its own image, with eight pairs of descending visual neurons to compile those thousands of images into one picture. Human color vision has three opsins, allowing us to see red, green, and blue region of the light spectrum. However dragonflies possess as many as 15–33 opsin genes resulting in around four-five opsins in the eyes of the adult dragonfly. These opsin genes differ in expressed between adult and larva, as well as between upper and lower regions of an adult compound eyes, linked with their a adult lifestyle of flying (an looking down), and the nymphs life of crawling and swimming (and looking up).The extra opsins allow them to also perceive UV light and the plane of light polarization. The large eyes encompassing the head allowing for 360 degrees of vision of their habitat, quite literally having eyes (or t least vision) in the back of their head.
The second is the mastery they have over their flight. Each one of the four wing, a beautiful bend of strength and flexibility, operate independently of the others, each with their own dedicated muscle group, similar to the mechanics of a 4×4 car millions of years before they were even thought of. This independent operation allows for greater efficiently and agility with movement in all directions is possible, even backwards, sideways and upside down (not damselflies) if needed. The video shows in slow motions a dragonfly capturing a fruit fly, calculating where it will be and using those powerful wings to be a the point where the fly will simply fall into its trap. There really was no chance. Dragonflies and damselflies however can themselves be hunted upon by birds, amphibians, fish and larger dragonflies. to which the skill above also prove invaluable.
The distribution of various groups of Odonata is highly variable. Some travel and migrate thousands of miles while others never leave their natal pond far behind. While they all require fresh water, some like still calm ponds, some like streams and some like marshy environments. Their presence is a good indicator of good water quality, because of all their millions of years of survival water pollution is now becoming a source of worry. This not only effects them directly but also their food source. Water is one of the most precious resources on this planet yet faces many direct and indirect contaminates such as oil, acid rain, acidification from uptake of carbon, soil leaching and pesticide and herbicide run off. Changes in after temperature can also effect the more sensitive species. However many projects world wide go on to help promote these fascinating insects and I would highly recommend anyone to try to make a wildlife friendly pond.
As I sit by the waters edge trying to capture these enamel beauties with the camera (of which the best results are below). whose adult lives are so sort yet their history so long, I hope that in the future there will still be many of these perfect areal predators to enjoy.