Males of this species are light blue and black. Females are yellowish, later brownish.
This video from Britain says about itself:
Dragonfly Week 2017
2 July 2017
A look back at Dragonfly Week 2016 at WWT London Wetlands. This year it will be 15th-23rd July and the British Dragonfly Society will be there to offer expert info and advice. Take the Dragonfly Challenge while you’re there!
By Peter Frost in Britain:
Dragons in the sky, near you
Friday 21st July 2017
As it is national Dragonfly Week PETER FROST investigates these complex, intriguing and, at the same time, beautiful insects bequeathed to us by most distant prehistory
“I saw, once, an endless procession, just over an area of water-lilies, of small sapphire dragonflies, a continuous play of blue gauze over the snowy flowers above the sun-glassy water. It was all confined, in true dragonfly fashion, to one small space. It was a continuous turning and returning, an endless darting, poising, striking and hovering, so swift that it was often lost in sunlight.”
That was Northamptonshire born novelist HE Bates writing in 1937 — in his series of nature essays Down the River — in what have been described as endless summers as dark war clouds gathered over Europe.
Bates would become much better known for his wartime books such as Fair Stood the Wind for France and after the war for his Darling Buds of May novella and sequels that became the hugely popular TV series.
While ambling beside your favourite canal towpath, riverside walk or village pond there’s nothing like the colourful, iridescent flash of a dragonfly to tell you that summer is here.
This is national Dragonfly Week and this Sunday July 23 there is a special dragonfly event at the National Trust’s Wicken Fen in Cambridgeshire. You can join experts to learn more about some of our most spectacular wildlife.
There are 57 recorded species of Odonata in Britain, made up of 21 damselflies and 36 dragonflies.
Damselflies are smaller and weaker flying relatives of dragonflies.
So what is the main difference between a dragon and a damsel? The most noticeable is that most dragonflies rest with their wings open while damselflies rest with their wings folded together over their body. Damselflies are also weak fliers and tend to stay close to water.
The loss of garden ponds, concreting over the countryside and intensive farming has already lost us at least three species in the last 45 years and more are under threat.
The insects are also extremely sensitive to the weather and find it difficult to adapt to climate change.
The National Trust is so concerned about the issue that in 2009 it opened the UK’s first Dragonfly Centre at Wicken Fen in Cambridgeshire in order to create wetland habitats where rare species can be protected and studied.
Chris Packham — the often outspoken BBC Springwatch presenter — told us more species could be lost without action: “The loss of wetland habitat throughout the UK is having a massive impact on the long-term survival prospects for many dragonfly species.”
Adult dragonflies are amazing creatures with huge multifaceted compound eyes each made up of nearly 24,000 individual ommatidia or simple eyes.
They have two pairs of strong, transparent wings, sometimes with coloured patches, and an elongated often amazingly colourful and iridescent body. They are remarkably agile fliers.
Some of our native dragonflies are really large. In Britain some such as the Emperor and Brown Hawker reach a length of about 85mm (3.5in) and a wingspan of over 120 mm (5in).
Fossil evidence shows there were once dragonflies with wingspans up to about 750mm (30in). They first appeared between 250 and 300 million years ago and they have changed very little since then.
They are are fierce predators both in their aquatic larval stage — when they are known as nymphs or naiads — and as adults. Several years of their lives are spent as nymphs living in fresh water. The adults may be on the wing for just a few days or weeks.
They have a uniquely complex sex life involving indirect insemination, delayed fertilisation and sperm competition.
During mating, the male grasps the female at the back of the head or on the prothorax and the female curls her abdomen under her body to pick up sperm from the male’s secondary genitalia at the front of his abdomen.
Romantically the two curved bodies can form a heart shape while the actual coupling takes place.
Dragonflies are some of the swiftest flying insects, with hawker dragonflies recorded at a top speed of over 20 miles an hour. They also display high manoeuvrability with some species capable of hovering and even flying backwards.
With their giant complex eyes dragonflies live in a world highly influenced by sight. The shape of those eyes allows them to see ahead, behind and to the side all at once. They also have great colour vision, which enables them to spot each other.
As well as the main two large eyes, they have three more located on the top of their heads in a triangle formation. These are simpler and detect very little detail and are specifically attuned to light intensity.
This ability allows the three eyes to detect information to assist flight, such as altitude and orientation while completing complex flight patterns.
Rather than being designed for walking dragonfly’s legs are positioned to catch prey in mid-air. Once a meal is trapped, the dragonfly’s forward facing legs are capable of holding up the prey item to its mandibles.
They eat small flying insects such as flies and mosquitoes — as well as butterflies and even smaller fellow dragonflies.
Their aquatic larvae are voracious, hunting various invertebrates, as well as tadpoles and even small fish. They alter their colouration between moults to blend in with their surrounding environment which helps them to stay hidden away from predators and prey too.
Want to help our British dragonflies? Or just find out more about them? The British Dragonfly Society is the place to start.
New research has shown how a dragonfly’s brain anticipates the movement of its prey, enabling it to hunt successfully. This knowledge could lead to innovations in fields such as robot vision: here.
This 201 video fgrom Brazil is called Zenithoptera lanei male and female. By Ruy Penalva.
From Science News:
The blue wings of this dragonfly may be surprisingly alive
Adults go to great lengths to shine blue
By Susan Milius
7:00am, June 30, 2017
An adult insect wing is basically dead.
So what in the world were tiny respiratory channels doing in a wing membrane of a morpho dragonfly?
Rhainer Guillermo Ferreira was so jolted by a scanning electron microscope image showing what looked like skinny, branching tracheal tubes in a morpho wing that he called in another entomologist for a second opinion. Guillermo Ferreira, then at Kiel University in Germany, showed the image to a colleague who also was “shocked,” he remembers. A third entomologist was called in. Shock all around.
The shimmering, bluest-of-skies wings of male Zenithoptera dragonflies might be unexpectedly and fully alive, Guillermo Ferreira says. That bold idea will take some testing. So for now, he and colleagues report the unusual tracheal respiratory system, the first in any insect wing as far as they know, in the May Biology Letters.
Wings of insects start as living tissue, but as the creatures take their adult form, cells die between the strut work of supporting wing veins. The dried-out zones can go cellophane-clear or cover themselves in color, bordered by the vein network like the glass pieces in a cathedral window. The veins, as they’re called, have their own respiratory tubes, nerves and such. But entomologists thought the rest of an insect wing would be no more alive and in need of oxygen than toenail clippings.
Living, breathing wings might help explain how South America’s four or five species of morpho dragonflies make such complicated blue color, says Guillermo Ferreira, now at the Federal University of São Carlos in Brazil. Blue pigment, rare in nature, is nowhere on these wings. Instead, the wings, perhaps powered by abundant oxygen, create a living layer cake of light-manipulating doodads.
In the tough inner layers, male Z. lanei wings form nanoscale spheres sandwiched between blankets of black pigment–filled nanolayers. This setup can enhance reflections of blue light and muddle other wavelengths. On top are two more light-trick layers, each made of wax crystals. The uppermost crystals, Guillermo Ferreira found, are shaped “like little leaves.”
Better blues might help a male intimidate rivals for breeding territory around the edges of their palm tree swamp homeland. Male dragonflies don’t just dart and bluff. Guillermo Ferreira often sees a male “rushing toward the rival, grabbing the wings, biting the wings and then sometimes biting the head.”
In spite of the world-class color nanogadgetry, males aren’t known for courtship displays, he says. “The female just flies in, and he just grabs her.”
This video from the USA says about itself:
Texas Dragonflies 2011
A selection of Dragonflies filmed during a week in October 2011. The key targets for me were Green Darner and Blue Dasher as both have occurred as vagrants in the UK. These two species are very common in the States. Thornbush Dasher was also a personal favorite. The bulk of the footage was taken at Santa Anna in the Lower Rio Grande Valley.
From Rice University in the USA:
Dragonflies reveal how biodiversity changes in time and space
Ecologists helps measure impact of top predators through time
June 30, 2017
Summary: In one of the first studies of its kind, ecologists monitored East Texas dragonfly communities for years to show that simple mechanisms could be used to predict how biodiversity varies across time and space.
An ecological filter in a pond, such as voracious fish that feed on dragonflies and damselflies, can help ecologists predict how biodiversity loss may impact specific habitats, according to Rice University researchers who spent four years studying seasonal changes in ponds across East Texas.
In one of the first studies of its kind, the scientists show that strong environmental “filters” — in this case, predatory fish — cause dragonfly and damselfly communities to vary regularly from year to year and season to season in ponds across East Texas. The results, which appear online this week in the journal Ecology Letters, show how an ecological filter can help ecologists predict how biodiversity loss may impact specific habitats.
Thousands of Earth’s species are becoming extinct each year and the rate is increasing. Scientists have struggled to predict consequences of biodiversity loss, in part because of the uncertainty about natural variations in composition of communities across time and space.
“Ecologists tend to think about biodiversity in space — we locate biodiversity hotspots and use maps to show how biodiversity varies in different habitats — but not in time,” said Volker Rudolf, associate professor of biosciences at Rice and the lead scientist on the new study. “In reality, biodiversity changes over time just as much and in many different ways.
“There are ecological theories that suggest that community dynamics should be connected in both time and space, but we typically just infer the temporal dynamics from the spatial patterns,” he said. “In a sense, people have sort of done this backward. They assume that if these dynamics happen over time, then here’s what we should see in space. In our case, we don’t assume. We actually show what happens.”
In their study, Rudolf and his students collected and analyzed more than 18,000 insects, amphibians and fish in quarterly visits each year from 2011 to 2015 at 45 remote ponds in the Davy Crockett and Angelina national forests about 80 miles north of Houston.
Study co-author Nick Rasmussen said dragonflies — and their diminutive cousins, damselflies — were the perfect organisms to study biodiversity in East Texas because more than 60 species live there.
“We’ve got a lot of the tropical species, and a lot of the North American species, and if you go out and look at a specific pond, you’ll see there is a lot of variation in what species is where,” said Rasmussen, a postdoctoral researcher at the University of California, Davis, who earned his Ph.D. at Rice in 2012. “There’s a pretty good understanding that specific factors can influence what species show up in a given pond, and those could be things like fish, canopy cover, water temperature and how often the pond dries out. But on top of that, everything is seasonal. Species change with summer, winter and wet and dry seasons.”
One of the main things the team wanted to investigate was the extent that each pond varied, not just from season to season but also from year to year during the same season. By returning each fall, winter, spring and summer to the same ponds for four years, they quantified four sets of season-by-season changes (i.e., spring to summer) as well as four sets of year-to-year changes (i.e. summer to summer) for each site.
In analyzing the differences, Rudolf’s team found systematic differences in the temporal and spatial patterns of dragonfly diversity across ponds with different top predators. In ponds that were associated with the presence of predatory fish like bass, the top predators brought an order to both the type of dragonflies that were able to live in a pond and how dragonfly communities changed over the seasons and years.
“If you look at any of the fish ponds, you can observe dramatic changes in the composition of communities from season to season, but the changes are pretty consistent among years for each pond with the same fish predators,” said study lead author Benjamin Van Allen, a postdoctoral researcher at the University of California, San Diego, who earned his Ph.D. at Rice in 2014. “Looking at one fish pond throughout the year gives you a good idea of what happens in the rest of them.”
In contrast, the ponds that lacked fish showed far more diversity from pond to pond in the types of dragonfly species that were present. They also failed to change as consistently with seasons and years as ponds with strong top predators. Without a strong filter, the community of dragonflies in ponds that lacked fish “drifted” over time and did not go back to the same place each year, Van Allen said.
Co-author Chris Dibble, a postdoctoral researcher at Indiana University who earned his Ph.D. at Rice in 2014, said, “What this tells us is that if we want to get a sense of total biodiversity in habitats with strong filters, then we should pick a few example sites and measure them several times throughout the year. If no strong filter is present, then our study suggests that it would be more efficient to measure as many sites possible, but at fewer points in time. It’s also important to note that strong filters can also include strong climatic or environmental conditions, in addition to biotic factors like predators.”
Rudolf said the study suggests that ecological stress brought on by overfishing, overhunting, habitat loss and climate change could have very different effects on habitats with and without filters. He said the study shows how important it is for ecologists to account for such differences as they seek to quantify and conserve remaining biodiversity.
“These spatial and temporal components are really connected,” he said. “A common mechanism can drive them. In a larger context, that means that we can use simple rules to infer something about biodiversity and how it changes over time and space in various habitats and patches.”
This video from England says about itself:
Common Hawker Dragonfly (Aeshna juncea)
13 February 2015
Common Hawker Dragonfly, filmed in the New Forest, Hampshire, UK. One of the rarest species in the New Forest, occurring only sporadically in a few isolated locations. Video includes male and female of the species, plus a mating pair.
From New Scientist:
27 April 2017
Female dragonflies fake sudden death to avoid male advances
By Sandrine Ceurstemont
Rassim Khelifa from the University of Zurich, Switzerland, witnessed the behaviour for the first time in the moorland hawker dragonfly (Aeshna juncea). While collecting their larvae in the Swiss Alps, he watched a female crash-dive to the ground while being pursued by a male.
The female then lay motionless on her back. Her suitor soon flew away, and the female took off once the coast was clear.
“I was surprised,” says Khelifa, who had never previously seen this in 10 years of studying dragonflies.
Female moorland hawkers are vulnerable to harassment when they lay their eggs since, unlike some other dragonflies, they aren’t guarded by their male mates. A single sexual encounter with another male is enough to fertilise all eggs and copulating again could damage their reproductive tract.
Khelifa found that the females often retreat to dense vegetation near ponds at this time, probably to hide. And they often act dramatically when they emerge.
He observed 27 out of 31 females plummeting and playing dead to avoid males, with 21 of these ploys successful. Plunging at high speed is risky though, and according to Adolfo Cordero-Rivera at the University of Vigo in Spain, it may be a strategy that they use only in areas with lots of dragonflies. “Females may only behave in this way if male harassment is intense,” he says.
Few animals have been caught feigning death to trick suitors. The behaviour has been seen in a species of spider (the males use it to improve their chances of mating), two species of robber fly and a type of mantis.
Playing dead to avoid predators, however, is more common and has been observed in dragonflies. “It’s likely that females expanded its use to overcome male coercion,” says Khelifa.
Khelifa is interested in finding out whether the behaviour is unique to species that lay eggs alone or whether it is more widespread. Using extreme tactics to resolve sexual conflict isn’t unique to moorland hawkers: in their damselfly relatives, for example, females eat their partner.
The insect was discovered in 2015, during a joint Bhutanese-Dutch expedition in eastern Bhutan.
Its name is Gyalsey emerald spreadwing dragonfly. Gyalsey means ‘prince’ in Bhutanese. The new species was named after the young crown prince of Bhutan; on his first birthday, the dragonfly’s name became known.
113 dragonfly species are known from Bhutan.