Willow Emerald damselflies: What’s all the fuss?


If you happened to be at the reserve on the 7th of October, you’ll no doubt have been told that we saw Old Moor’s first Willow Emerald Damselfly that day. While I failed to photograph it on the day, I do have these images from another location earlier this year.

Willow Emerald, Cleethorpes, July 2021

This was an exciting find for me, as the species has had an explosive growth in the UK in the last couple of years, after a decade confined to the extreme south of England. There were only three sightings before 2009, and one of those was dead. Then over 400 were seen in Suffolk in 2009, and that was seen as the start of their rapid colonisation.

 Let me put this another way: they have been here only slightly longer than Little Mix.

In 2019 there was a rapid increase in their range up the East Coast, and this led to the species turning up on our doorstep.

 It was only last year that it first appeared in Lincolnshire and East Yorkshire, and I saw my first one in Cleethorpes back in July after a focused search. Since August, they’ve been seen around Goole and Thorne with increasing frequency.

However, I was actually watching the Southern Hawkers the other day when one casually floated into view. It stayed for only a few seconds before flying off again, but stopped to give some really clear views before it went. It’s my 21st species of dragonfly and damselfly seen at Old Moor.

There are a few things about the Willow Emerald that makes them stand out from other damselflies. Not least of all is their habit of laying their eggs out of water, directly into the twigs of live trees! The eggs spend the winter in the tree, and in the spring the prolarvae (really tiny larvae which look absolutely nothing like the adults) hatch out and drop straight into water, sometimes from several feet.

They are pretty hardy, and appear later in the year than most other damselfly species, lasting into November.

To help them deal with the tough bark, females have a fine saw-toothed egg-laying mechanism which allows them to cut straight through the bark. If this sounds damaging to you, you’re not wrong: Willow Emeralds leave a series of scars on twigs that can be visible for a few years after egg laying has taken place.

And then there is the colouring. Willow Emeralds are almost perfectly matched to Willow leaves, with a metallic green upper (which can take on a coppery colour in some lights) and lighter yellow-green underside. They’re like little camouflaged SAS troops. The saving grace for the keen dragon hunter is that they are slightly larger than the (currently) more common Emerald, the males of which have blue eyes and a waxy bloom that appears as they mature. If you see blue on a suspect, it’s not a Willow Emerald. The best feature to separate them from other damselflies is the long spur-shaped marking on the side where the two colours meet.

Willow Emerald, Cleethorpes, July 2021.

It’s possible that the reason they’ve appeared to spread so quickly is that they are so very difficult to spot. They do tend to hang out in trees, and because they prefer to use willow and alder on the margins of ponds they aren’t always easy to get near.

Now obviously a single sighting is hardly proof of a healthy population, but it’s quite likely that they’re out there in decent numbers just waiting to be found.

I’ll race you.