Odonata 1

Rooksbury Mill LNR, Andover.

Damselfly Exploration, early June.

John Solomon

Rooksbury Mill Local Nature Reserve is situated south of Andover town centre and adjacent to Watermills Park.  It has two lakes which are fed by the River Anton and were created soon after World War II through gravel extraction.  The site now encompasses a range of habitats including areas of wet woodland, chalk grassland, scrub, riparian habitats, two large lakes, ponds and a stretch of the River Anton. [TVBC website]

Odonata of Andover and the Surrounding Area

Introduction

Odonata is the Latin term for the insects known more commonly as Damselflies and Dragonflies. While superficially very similar they do differ in several ways. Firstly, Dragonflies are larger than Damselflies and when they rest they always do so with their wings stretched out from the body. The nymphs, the immature forms that live in rivers, streams, lakes and ponds, add another major difference in the positioning of the gills they use to breathe. Damselflies have three feathery gills, known as caudal lamellae, attached to the end of their abdomen. Dragonfly nymphs, on the other hand, have their gills inside their abdomen, actually taking water in and then expelling it through the rectum. If necessity demands they can eject this water very forcibly to give them a short burst of speed, perhaps to escape a predatory fish.

Being insects all Odonata larvae have six legs, an exoskeleton with wing buds and a hinged jaw that allegedly provided the inspiration for the Alien in the films. They live in submerged vegetation or even down in the silt and sediment at the bottom of bodies of water. They are very active hunters, preying on anything they can catch and overpower. For Damselflies and young Dragonflies that may be Water-Fleas and other almost microscopic creatures, but larger nymphs will go after a wide menu including crustaceans, tadpoles, leeches and even small fish.

As insects they cannot grow by simply getting larger, their exoskeleton prevents that, so at regular intervals they shed the exoskeleton they have replacing it with a new one a size larger. The smaller Damselflies will go through 5 such moults but the larger Dragonflies might moult as many as 14 or 15 times. Similarly, the larger the insect the longer it takes for it to feed up and reach the state of emergence. The Common Emerald Damselfly lays its eggs towards the end of Summer and they do not hatch until early the following Spring. The larva then feed voraciously emerging only 2-3 months later as adults but this is exceptional. Most Damselflies take 1-2 years to reach the point where they are ready to leave the water and take to the sky, but this is dependent upon the availability of food. Larger Dragonflies, such the Golden-Ringed, can remain as nymphs and feeding up for as long as 5 or 6 years.

When it is time for the emergence the insect climbs up out of the water, often using a reed. The exoskeleton of the nymphs splits and the adult insect starts to push itself out. It pauses once the head, thorax and legs are free, waiting for half an hour or so to allow the fresh and soft new exoskeleton to harden. Once the legs are firm it then hauls out the abdomen. By pumping fluids around the body and through the veins of the wings the abdomen is extended and the wings reach out into their full glory. The fluids are then drawn back into the body and the wings and exoskeleton allowed to dry and set. This is a crucial period in the insect’s life. Not only is it intensely vulnerable to any predator but if the expansion of the wings is compromised, for instance by being restricted by vegetation, then the wings will not form properly and it will not be able to fly … and if it cannot fly it cannot catch prey and feed.

The newly emerged adult, or teneral, may not necessarily have its full adult colouration and patterning. Dragonflies are often pale green while the Damselflies offer a variety of different colours, the female Blue-Tailed Damselfly being an excellent example, and the insect may take around a week before the full, adult pigmentation is seen. This can make identification interesting.

With wings dry the insect now heads skyward to take its place as one of the most deadly predators on Earth. Their hunting success rate has been estimated at 95%, so if you are a small flying insect and a Dragonfly or Damselfly decides that you are lunch, then you are truly lunch. They owe their devastating prowess in part to their four magnificent wings. They can operate all of them independently through a wide range of movement, enabling them not only to fly forwards, upwards or sideways but also to hover and even fly backwards. Furthermore, they are able to execute a change in direction at blinding speed. To guide this amazing flying ability and pinpoint their prey they have remarkable vision. All insects use what are known as compound eyes, being formed of a series of what are effectively tubes, known as facets or ommatidia. These contain light sensitive proteins, or opsins, which respond to different wavelengths of light. In the case of Dragonflies and Damselflies there four or five different opsins enabling them to see beyond our own spectrum and into such optical regions as ultra violet. Each eye can contain up to 30,000 of these ommatidia and, thanks to their round structure, the two eyes give them a fully spherical field of vision. Last, but not least, careful examination of those 6 legs will reveal what look like hairs or bristles, but they are not. Instead they are stiff, hard spikes of the chitin that forms the insect’s exoskeleton. When it attacks its prey it wraps them up in its legs, which form a cage known as the ‘basket’, and those spikes help hold it secure. Damselflies and Dragonflies really are the dragons of the insect world.

As adults their main aim in life is to breed. To this end male Dragonflies will often commandeer a stretch of bank or reed bed which they will patrol relentlessly, investigating any intruder. They will drive away possible rivals but the insect will endeavour to mate with any suitable female that passes through, often quite forcibly. Apart from the Large Red most of the Damselfly species found in the area are not so territorial, mainly living in large groups throughout the reed beds around the local lakes, although the males are just as bent on fulfilling their obligations. The weather can be conducive, or otherwise. The hot early summer of 2018 filled the reeds and even the air with courting couples, while the rather lower temperatures and gustier wind of the same period a year later, in 2019, saw a much lower level of activity.

Male Odonata have two sets of sexual organs with the primary sperm producing organs situated at the very base of the abdomen. The insect transfers sperm from here into what might be thought of as a pouch on the underside of the second section, known as the ‘accessory genitalia’. During mating the male holds the female by the back of the ‘neck’ using the claspers at the very tail end of his abdomen. If the female is agreeable she then reaches the tip of her own abdomen forward and up, so it meets the male’s accessory genitalia, and the sperm is transferred. This position is technically known as in copula and more commonly described as ‘the wheel’, although any observer will see from the shape the insects form that perhaps the term ‘the heart’ would be more fitting in more ways than one. The length of time the partners remain in this position varies considerably and has little to do with the size of the insects. The Blue-Tailed Damselfly is one of our smallest but the pair may remain attached to each other for up to 6 hours, while in the Chasers it lasts only a few seconds and can even take place in a brief mid-air encounter.

The fertilised female will spend most of her adult life engaged in laying eggs. Most species lay their eggs in floating or emergent vegetation, sometimes depositing them directly into the water but more often using a needle-like ovipositor to inject them into plant stems. A Damselfly will lay hundreds of eggs during the 2-4 weeks of her life and a Dragonfly, which may live for couple of months, could lay thousands. To give an idea a Banded Demoiselle was observed laying 450 eggs in one 45 minute session, while another unidentified Dragonfly was seen hovering over Rooksbury Lake laying at the rate of one a second for 7 or 8 minutes, giving a total of between 420 and 480 eggs. Normally the eggs hatch within 2-5 weeks although, as mentioned above, some species, such as the Common Emerald as well as some Hawkers and Darters, wait until the following Spring.

Damselflies

Dragonflies and Damselflies are insects, which means that, in basic terms, their bodies are formed of three sections. Their head, which is self-explanatory, holding those over-sized eyes, the crushing jaws and a pair of very small antennae. The mid-section is a large and solid box, known as the thorax, which has the wings on its upper surface, holds the powerful flight muscles, and has the under-carriage of the legs underneath. The third section is visually its tail, stretching out long and slender behind the insect, but is in fact the abdomen. In the Andover area there are two species of Demoiselle and eight of Damselfly. While the Demoiselles are reasonably easy to tell apart the Damselflies often have a blue male and a green female and it is only the careful study of the different colours and sometimes very slight and subtle variations in the patterns of the markings which enable differentiation. For identification it is also important to remember that the long abdomen is formed of ten sections. As mentioned above the male has accessory genitalia. This is effectively a bag seen as a small bulge found on the lower surface of section 2. In the description that follows there will often be references to sections 8, 9 and 10 where some of the minor but important differences between species can be found.

As a general rule Damselflies emerge earlier than Dragonflies and that is certainly so for the species found locally. They will start to be found in small numbers towards the end of May, rapidly growing the populations through June and into July, then gradually disappearing through August. All three of Andover’s lakes have healthy populations but they are easily the most numerous at Rooksbury, so head there, on a sunny day in mid to late June, and walk through the arched entrance from the car park through the hedge to the smaller lake. Follow the path round to the left and across the bridge and over the river. Now stop and look around you.

You will see small, blue Damselflies. They will be landing on the stinging nettles to your left, the vegetation in front of the bench ahead of you, that looks out across the lake, and in the weeds to your right. Some will even be landing on the path. At first glance they will all look much the same but slowly and carefully move in when one perches and examine it more closely. Then look closely at another. You will discover that there are, in fact, two species here. One has a blue thorax with blue markings all along its abdomen, towards the end of which there is a thick band of blue. This is a male Common Blue Damselfly which, as its name suggests, is very common. The other is a little bit smaller and although it, too, has a blue band towards the end of the abdomen this band is thinner, also although the thorax appears blue the abdomen is black with no apparent markings whatsoever. This is the Blue-Tailed Damselfly. We will look at the Common Blue first.

The sides of the thorax are a bold slab of electric blue. Atop this is a black stripe and then another bold stripe of blue. This top stripe is known as the antehumeral stripe and is another useful species identifier, particularly with Red-Eyed and Small Red-Eyed Damselflies as we will see later. The mature female of this Damselfly is an unimpressive grey-brown but when younger they come in rather more attractive blue and green forms. The pattern of the marking is very similar to the male, with the same bold colour on the side of the thorax and a similar antehumeral stripe, so it can be tricky to tell a blue female from a male. To do so look at the very end of the abdomen and you will see that while the male has a very blue band of colour wrapped around sections 8 and 9 on the female whatever the colour the band is broken on the top side. This is probably the most common UK Damselfly being well distributed and usually the most numerous, present everywhere from Lands End to John o’Groats.

The second most common Damselfly, both locally and nationally, is the Blue-Tailed. Stay where you are, near that bench at the edge of the lake, and look carefully at those small Damselflies around you with the finer blue-banded ‘tail’ and suddenly you will realise that they are not all the same. It is true that there are some there that have a blue thorax and a blue tail but there are others, with a green thorax and a blue tail, yet others with a brick-red thorax, a brown thorax, even lilac and an occasional one that doesn’t seem to have a blue tail at all. These are all Blue-Tailed Damseflies, and if you don’t see all those variations here you will do so as you go around the lake and search in the reeds.

To start with the male, a young male will have a green thorax and a blue tail. As he matures he will take on his full adult blue colouration. He keeps things simple, unfortunately the female of the species does anything but. A fresh, young female will either have a raspberry-red thorax or a lilac one, both having a blue ‘tail’. The raspberry-red form will gradually turn brown, including the blue ‘tail’, often passing through a very attractive golden phase. The lilac form is more complicated, the thorax either turning green and the band around the end of the ‘tail’ an olive or brown, or else the insect taking on a colouration to all intents and purposes identical to the male. The only way of telling the blue form female apart from the male in the field being to get a good enough photo or magnified view of the underneath of section 2 of the abdomen, which is where the male’s secondary genitalia will be found.

Move forward, perhaps to stand on the concrete over the outflow from this smaller lake, and you will see floating vegetation very gradually getting caught in the slight current and dragged towards the exodus beneath your feet … and there are Damselflies here, playing as if hopping from one short-lived raft to the next. Of course, you recognise the Common Blue and Blue-Tailed, but there is another. At first it looks like Common Blue, but there is a darkness over its shoulders, almost as if it is wearing a black cloak. Then, if you are patient, one will float close enough for you to see the eyes. Red! Very aptly, this is the Red-Eyed Damselfly and the blue ones you see are the males. If you are lucky you will see a mating pair, the male flying them from short perch to short perch, and you will find that the female he is linked to is green. You find them easily here but to actually see them properly we are going to have to get far closer, and that means finding them on land.

Turn to your right and follow the footpath anticlockwise around the lake to the second footbridge over the stream. Don’t forget the Red-Eyed Damselflies but here we will take a very slight detour and walk onto the bridge. Beneath you is thick with Water-Cress and reeds reach the water’s edge along both banks but scan around and very quickly you will glimpse a fluttering, almost like a butterfly’s wings. When it lands it holds its wings along the length of its body and you will see they are clear with a dark blue, almost black, smudge of a thumb print across the middle of them. The body itself looks a dark and ever so metallic blue. This is the male Banded Demoiselle, a lover of streams. Wait and keep searching and soon enough you will see another similar insect, but this one looks green, its body still very metallic. This is the female of the species. This Demoiselle is supposed to prefer slow-moving water courses but is evidently very happy along the chalk streams of the Test Valley.

Still on the bridge scan carefully around. This time of year, as mentioned above, is more the time for Damselflies but there is just a chance that you will see one of the earlier emerging Dragonfly species and here is a good place to spot one of them. This is the striking and rather handsome Golden-Ringed, with a black thorax and black abdomen strongly marked with contrasting yellow. Unlike most Dragonflies, which prefer still water, the Golden-Ringed likes streams and rivers. The end of the male’s abdomen has a swollen, almost club-like appearance, easily seen if the insect lands and allows you to move carefully closely. The abdomen of the female, on the other hand, is thicker along the whole of its length and straight right to the end. This is our second largest Dragonfly species, for our largest please read on.

Back to the path and follow along beside the bank of reeds on the right examining as you go. There will be plenty of Common Blues and Blue-Tailed, but stop around two-thirds of the way along. Searching the reeds you should soon start spotting blue Damselflies with those remarkable red eyes. Yes, Red-Eyed Damselflies and here, on the land, you can very slowly move closer and get a good look at them. This is where it really does help to have a camera. This will enable you to get a photo and then, wonder of the digital age, zoom in on the image on the viewing screen on the back and see what it actually is that you’re looking at. With this insect the first thing you will notice is that there is no blue antehumeral stripe, instead the top, or back of the thorax, is completely dark, almost black. That is why when they are flying it almost looks as if they are wearing a black cloak. Next, study the block of electric blue that covers the side of the thorax and you will see a small finger of a black marking reaching into the blue. This known as the Coenagrion Spur and is a strong identifying feature present on three species around the local lakes, two of which are found here. Now hunt for green Damselflies and, when you find them, examine the eyes and start taking photos. The female’s eyes are not as obviously red as the males but they are still discernible, what the photograph will enable you to do is look at the antehumeral stripes on top of the thorax. Unlike the male the female does have these but they are not full length, reaching only about half way backwards along the length of the thorax. If you are really lucky you may discover a third version of this insect. This looks like a female, having eyes that are reddish but not as strikingly so as the male, although the colour of the markings is more a yellow, sometimes quite strongly so. If you can get a good look at the top of thorax, where the female should have that short antehumeral stripe, you will get a clue as to what it is. Just like the male of the species there is no trace of that stripe. This insect is actually a very freshly emerged, or teneral, male Red-Eyed Damselfly.

Now start focusing on those insects that appear to be male Common Blues. With experience the very end of the abdomen, the “tail”, can appear slightly different but it is best to take a few photos of different insects. Eventually you will find one that looks like a Common Blue and has the same blue eyes but, like the Red-Eyed, it has that little black finger, or Coenagrian Spur, reaching into the block of blue on the side of the thorax. This is a male Azure. Similarly to the Common Blue the female comes in either a blue or green form and, exactly as with the female Common, the blue banding towards the end of the abdomen is broken giving a clear differentiation from the male. However, both sexes are very similar to their Common Blue opposite numbers underlining how useful a camera can be for accurate identification.

Walk on now the few yards to where a kissing gate opens to the right allowing entrance to a bush-covered tunnel flanked by light wooden fencing. I call this “the walkthrough”. You will find Common Blues here but a favourite pastime of Blue-Tailed Damselflies is sitting on the top bar that has been warmed the sun. As you walk along stop and search the streams for Water Voles, particularly the first one, and examine the second one for Banded Demoiselles. You emerge onto the large lake and along the wooden walkway towards the bench, past the nettles and reeds on your right. The orange-flowered plant is Orange Balsam. This is native to North America and was imported to decorate herbaceous borders through the 19th and 20th centuries. As such species are prone to do it ‘escaped’ and is now widely found, often seemingly preferring proximity to water. The plant’s sap has medicinal properties with Native Americans using it to treat skin rashes, such as Poison Ivy, and the sap has proven fungicidal properties having been used to treat athletes foot.

If you can brave the nettles it is worth striking out through them towards the lake. You will find all the species we have met so far here but there is also just the chance of coming across a Large Red Damselfly. For a Damselfly this is, as the name suggests, a large insect and it is also very obvious and distinctive. There is only one other it could possibly be confused with and that is the Small Red Damselfly which isn’t found locally. It is quite unusual around Rooksbury, being much more likely to be seen at Anton and with a good population on Chilbolton Common. It likes ditches and thick reed beds and Rooksbury is not well-served by either.

This corner of the lake is a favourite place for the Dragonflies that will start emerging in force as we move through July but, as mentioned earlier, there are early species and this spot is just as good to see them. You may well see something flying low and fast across the water. A powdery blue with what seems to be a dark end to the abdomen. This is a male Black-Tailed Skimmer. Note how the name fits. It has a black tail and its typical flight pattern is to skim low across the lake’s surface. Often the insect will have chosen a vantage point, usually a twig or branch that juts out over the water, which it will return to repeatedly before shooting off again. Once located a careful creeping up on this special place will often allow an excellent viewing and, of course, an excellent photo-opportunity. The female is hardly ever seen but she is a striking black and yellow.

One other early Dragonfly might be found here. Clearly larger than the Black-Tailed Skimmer it will also show a different flight pattern. While it will occasionally drop low to the water it will also climb high and swoop around, then cruise, then suddenly accelerate – these insects can reach the best part of thirty miles an hour! Examining it as it flies past you will see a green thorax and a blue-marked abdomen, then you might notice that the abdomen is drooping slightly down along its length. This is an Emperor Dragonfly, not only our largest Dragonfly but the second largest in the world. It is very common around our local lakes and as they emerge and the numbers rise on a good day it is easy to count 15-20 or even more around Rooksbury. You are probably, but not definitely, seeing a male. The two sexes are very similar but the female appears a little paler.

Back to the path and don’t bother looking for Dock leaves to treat any nettle stings, they really don’t work! Follow the path around the bushes and the River Anton is now on the left. This is a favourite site for our now old friends the Banded Demoiselles, but there is another species here, too, so search the reds along the bank well. When you first find this you will think it is just another Banded but then, if it is male, you will see that the “thumb print” trademark on the wings seems to have taken over the whole wing, leaving it completely blue-black. This is a Beautiful Demoiselle, found in much the same places as the Banded but nowhere near as common. While the male is fairly easy to differentiate from the other insect the female is rather harder, although it becomes easier with familiarity. While the female Banded is green the female Beautiful is brown. This sounds rather dingy but these insects are very metallic and the wings are translucent, meaning that when the sun catches them just so she can be lit up like a golden jewel.

Continuing around the lake exercise your new-found knowledge. Blue-Tailed and Common Blues will be found in large numbers. Azure Damselflies are all round, often more  in the weeds, grass and nettles rather than right on the lake, but they do need a good sighting and ideally a camera to tell apart. Standing on the fishing piers will show you more Red-Eyed Damselflies as they love to be out over the water, resting on floating and emergent vegetation. You should also see many mating pairs, particularly Common Blues. 

There are three other species found in the Andover area at this time of year, one is an early emerging Dragonfly and the other two are Damselflies. The Dragonfly is the Broad-Bodied Chaser. The male is a soft, powder blue but the female is a rather more eye-catching yellow which, due to the similarity in size and colour, has seen her called the Hornet Dragonfly. They are occasionally seen at Rooksbury but the rarity of the sightings tends to suggest that they are not resident here. They are also seen occasionally at Anton but the local hotspot seems to be Charlton, although they tend to prefer small ponds, such as the garden variety, so it may be that those seen around the lakes are more likely to be breeding in your back garden! They are often seen a considerable distance away from water, certainly Harewood Forest in May is a good hunting ground.

The Dragonflies are found at Charlton and Anton lakes, one at each. Anton Lake has a secretive population of Common Emerald Damselflies. Up until recently although it was felt that they should be here none had been spotted, then, in 2018 the first was photographed and several have been caught on camera since. They particularly like thick reed growth in a pond with a susceptibility to drying out, or at least a large water level drop, over summer. As mentioned in the introduction they lay their eggs into reed stems, both below as well as above the water, later in the Summer where they remain over Winter. They hatch in the early Spring into what are known as prolarva which have no limbs and hop or wriggle around until they discover water. Here they moult and the more expected nymph-style larva emerges. They feed voraciously. Whereas most Damselflies spend one to two years feeding up those of the Common Emerald can reach maturity in as little as 8-12 weeks. The adults begin leaving the water in July. The species has never been seen at Charlton Lake or Rooksbury, probably simply because those lakes don’t have the reed beds the insect needs. So far it has only been sighted in the reeds around the south-east, or town end, of Anton Lakes, particularly in the reeds of the small ‘pond’ that is there, but it could also be present in the more extensive reed beds of the much larger ‘pond’ at the other end of the lake, by the car park and Charlton roundabout. Incidentally, this would also potentially be a good site for the Large Red Damselfly, but proper searching would require a boat!

Back in 2017 I took a photograph of what I believed was a mating pair of Red-Eyed Damselflies at Charlton Lake. It wasn’t a great photograph and came close to being dumped, but it was a mating pair, of which I only had one other equally poor example, so I kept it. In Autumn 2018 I was conducting an end-of-season culling of my photo-library and had heard that someone believed they had seen Small Red-Eyed Damselflies in the area, so I checked my own Red-Eyed photos rather more carefully. I was rewarded by finding that the photo of a mating pair that I had so nearly binned was in fact a photo of a mating pair of Small Red-Eyed.

These are extremely difficult to identify in the field, particularly as both Red-Eyed species like identical environments and even have a similar national distribution. On top of that they both like to spend their time away from the bank and out on the lake perched on floating and emergent vegetation and both have Coenagrian Spur on the side of the thorax. The females are rather easier to differentiate than the males, but, even so, a very good sighting with, ideally, a decent photograph is still necessary. Describing the female Red-Eyed above I pointed out that the antehumeral stripes were very short, running only half the length of the thorax. On the female of the Small Red-Eyed they boldly run the full length. The only difference between the males of the species lies in the blue marking running round the tenth, or last section, of the abdomen. On the Red Eyed this colour runs around complete while on the Small Red-Eyed there is a fine break in it on the top surface. Faced with this strong similarity probably the best way to be sure you are looking at a male is to find a mating pair and identify the rather clearer female! There have been no more certifiable sightings since, but this could be mainly down to no such vegetation being close enough to the bank of Charlton Lake to allow the requisite photo – in 2017 such vegetation was right by the bank by the car park, which was where I got the shot. I feel that they are probably present at the town end of Anton Lake but, again, the emergent vegetation they might land on is far too far away from the bank. It looks as though Anton Lake needs a boat to properly search two areas!

Happy hunting!

https://british-dragonflies.org.uk

This website allows identification of Odonata and one can search species by the adult’s flight time.