The Willow Emerald Damselfly

An animal to keep an eye out for this month is an insect known as the Willow Emerald damselfly. This article will not only introduce you to this little creature but will also give you some good words for Scrabble (other word games are available).

You may be familiar with larger dragonfly species that you can see whizzing across a lake or along a hedgerow, hunting insects on the wing. These are large impressive insects, often quite brightly coloured with large wings that you can hear in flight and that are held at right angles to the body when perched. A damselfly is a type of dragonfly but very different in structure and behaviour.

Damselflies are delicate, smaller creatures than their more noticeable cousins. They have a more fluttering gentle flight and usually stay close to vegetation, unless laying eggs into water. Most* hold their wings closed over their bodies when perched, something larger dragonflies never do, unless just emerged from their larval form.

At first glance you may not even notice a Willow Emerald Damselfly because they are green, they perch in green vegetation and may be quite motionless until you are close. Once you have noticed them you will see that up close, they are a metallic green colour with a lovely shine in good light. There is of course, more than one type of green damselfly in The UK (I refer you to the foot-note below). If this article sparks your interest you can learn more about the other species at The British Dragonfly Society‘s website.

Once you have established that you are looking at a green damselfly – how do you know you are looking at a Willow Emerald? Firstly, there will be no blue tip to the tail. Then, look at the wings. They usually sit with them half open and you can see a pale cream patch at the outer edges. This patch is brown in Common Emerald. For the Southern Emerald Damselfly this patch is half pale cream and half brown.

The Willow Emerald spends most of it’s life as a larva underwater, catching smaller invertebrates amongst the water weeds. The larva moults several times whilst in the water getting bigger each time and may remain in larval for two months to two years depending on the temperature of the water and the amount of available food. When the time of year is right the larva will wait in shallow water for a few days, beginning to breath air and getting ready for their final moult. They then emerge from the water and climb up nearby vegetation and it then takes around an hour or more for the damselfly to push it’s way out of it’s larval skin. The newly emerged adult is pale in colour and known as teneral until it develops it’s breeding colours it will then remain perched as it’s wings expand and dry. They are incredibly vulnerable at this stage as they are soft and weak and their wings don’t work well, not only can they not really fly yet but the slightest touch to their wings from raindrops or surrounding plants or even just a gust of wind is likely to damage them and prevent flight at all. The old larval skin is left behind on the vegetation and is known as an exuvia (no this is not one of the X-men), these empty shells often remain on the vegetation for quite some time and you can get an idea of how many dragonflies live unseen below the water by how many exuvia you can see on the plants around the water.

The female Willow Emerald lay their eggs into the bark of willows and other trees where they overhang water and the telltale scarring on the bark can show the presence of Willow Emerald even when there isn’t an adult in sight.

Until recently spotting a Willow Emerald was a surprising and rare occurrence. They only really colonised in any number in 2009 in East Anglia. Since then, they have undergone quite a rapid expansion for a little creature less than 5cm in length and can readily be found within Revesby Estate and surrounding villages. They can be found as far as North Yorkshire and as far west as Warwickshire.

So if you are walking along a river or ditch this month keep half an eye on the tall vegetation along the edge of your path and you may well see the little jewel that is the Willow Emerald Damselfly.

* but not all – because nothing is simple or straightforward in the world of ecology

Gillian Fisher, Ecologist