Willow Emerald Damselflies.
Saturday, 23rd August, 2025.
This morning, I made my habitual journey along the well-trodden grassy path which leads from our home down to the garden pond in the hope of seeing something of interest. The sun was struggling to emerge from an overcast sky, but it was warmer than the previous few days and the weather was forecast to improve as the day progressed.
I expected to see the usual selection of Common Darters, (Sympetrum striolatum), Ruddy Darters, (Sympetrum sanguineum), Blue-tailed Damselflies, (Ischnura elegans), and Emerald Damselflies, (Lestes sponsa), which had been frequenting the pond in previous days. I was, however, surprised to see two male Willow Emerald Damselflies, (Chalcolestes viridis), resting on a clump of Dutch Rush, (Equisetum hyemale), at the back of the pond. This was a species which had never been observed in our garden before.
The previous day, we had joined a group of Doncaster Naturalists’ Society members on a visit to Thorpe Marsh Nature Reserve to search for Willow Emeralds, a trip which proved unproductive, partly due to the somewhat inclement weather conditions. It was, therefore, a little ironic to come home and find them on our garden pond!
We had also accompanied a group of Doncaster Naturalists members on a visit to Austerfield Mosaic Reserve, on the 12th of August, with a similar mission. On this occasion, a very warm day, we were lucky enough to see several male Willow Emeralds basking in the sun on vegetation around the edges of one of the ponds. The reserve is not far from our home, so we knew they were in the general vicinity, but seeing these habitat-specific Damselflies on our modest garden pond was quite unexpected.
The following morning dawned hot and sunny and our pond was busy with the frantic activity of several species of Dragonflies. I was delighted to see numerous Willow Emeralds had arrived, and were occupying the pond margins, basking in the sunshine, adopting their habitual resting position with wings held at 45 degrees to their bodies, unlike most other species of Damselflies which hold their wings together along the length of their bodies. They were easily distinguished from the Emerald Damselflies, which were also present, because of their long metallic-green abdomens, and pale pterostigmata, outlined in black. Willow Emeralds also lack any blue colouration, and have a prominent green spur marking on the sides of their thorax and the males have pale anal appendages with black tips. There were several mating pairs, and a mis-matched pair consisting of a male Emerald Damselfly and a female Willow Emerald Damselfly, a case of enthusiastic opportunism rather than the possibility of successful breeding.
Willow Emerald Damselflies, (family Lestidae), are unique in the UK, being the only species of Odonata to lay their eggs on the branches of trees, their preference being Willows and Alders.
Breeding activity can be confirmed by the presence of the ladder-like scars made by the female as she inserts her eggs under the bark of the thinner branches of trees.
Ours is not a natural pond, but constructed with a liner. Due to the potential hazards of root penetration of the waterproof membrane, there are no trees close enough to the water’s edge to provide the overhanging branches which Willow Emeralds require for oviposition, and the successful progression of larvae to the aquatic phase of development after accessing water. This being the case, I wondered where the mating pairs could possibly lay their eggs, thus furthering procreation.
Throughout the day, I monitored their activity, and noticed a couple of pairs, still in the mating ‘wheel’, visiting the dead flower stems of Meadowsweet, (Filipendula ulmaria), plants, which were growing in pots in the pond margins. It appeared very much as though the females, still clasped at the back of the head by the guarding males, were attempting to lay their eggs on the desiccated stems. I had read previously, that they do not lay their eggs exclusively on Willow and Alder, but may actually utilise a wide range of species of trees and other woody plants, the main criteria being that the branches overhang water. On sharing my information with members of the Yorkshire Dragonfly Group, I learned that Willow Emeralds had been observed ovipositing onto Loosestrife, Mugwort, and Buddleia. They are also known to use Hawthorn and Field Maple, therefore, it was entirely feasible that they might attempt oviposition onto Meadowsweet stems. We also have Purple-loosestrife, (Lythrum salicaria), planted around the pond and, although I didn’t observe any of the pairs visiting these plants, we decided we would leave the old stems without cutting them back incase oviposition signs develop. This may be something to watch out for in future.
Willow Emeralds have a very interesting lifecycle. Females lay their eggs in pairs, inserting them underneath the bark along thin branches, (usually of pencil thickness), which overhang water. The eggs overwinter beneath the bark to avoid predation, and hatch in the following Spring, when they drop into the water and develop very quickly as nymphs, emerging just three months later as adults.
The British Dragonfly Society’s ‘Willow Emerald Watch’, charts the range expansion of the species, from a couple of records in 1979 and 1992, an individual in Suffolk in 2007, to four hundred in 2009 in the S.E. Suffolk, N.E. Essex area. Since then, they have spread rapidly, reaching new counties every year. In 2019, a big surge along the east coast, saw them reach as far north as Harwood Dale in N. Yorkshire. The north-west spread has continued with significant colonisation across the country. 2025 saw the first official breeding records for Wales and the species continued its spread into the south-west reaching Cornwall, Dorset and Somerset.
Willow Emeralds are best seen on warm, dry, windless days between July and October. Outside of the flight season, their presence can be confirmed by the horseshoe-shaped scars produced by the eggs, laid in pairs in a ladder-like formation along the length of tree branches which overhang still or slow-moving water, thus facilitating entry to the water body by the larvae. Should the larvae, on hatching, happen to fall on dry land, they have the remarkable ability to ‘spring’ across the land until they meet water.
Having discovered the influx of Willow Emerald Damselflies on our pond, and realising the habitat was far from ideal for the chance of a breeding population to establish, we determined to attempt to make the pond-side environment more conducive to the requirements of this species. As an experiment, we decided to introduce a young, potted Weeping Willow tree which we had rescued from an area of our garden where it was struggling to grow in the drought conditions which we had experienced since it was planted. It had recovered well after being potted and watered regularly, and reached a height of around 2.5 meters. We were able to bury the pot at the rear of the pond and allow the pendular branches to overhang the water surface. To our delight, we observed a copulating pair fly into the Willow almost immediately. Our hopes were that this would encourage a female to lay her eggs into the bark and we might be afforded the opportunity of close observation of the lifecycle of this species throughout the following year. However, after some considerable time of inactivity, the pair was seen to fly off, the male still clasping the female. I was able to track their flight towards a large Field Maple, (Acer campestre), growing in our garden approximately twenty meters from the pond. The conjoined pair alighted very high up in the tree, and it was impossible to see if oviposition took place due to the dense covering of foliage.
It will be interesting to see what happens in future years, and if oviposition scars are found on any of the woody plants in the garden. Since this considerable influx of Willow Emeralds to our garden, with numbers rising to double figures visible at any one time, over the weekend of 23rd-24th August, only a few individuals have been spotted. Whether or not they return next year, we will have to wait and see, but with favourable weather conditions, and the continued country-wide colonisation of the species, we remain hopeful.
The arrival of the Willow Emerald Damselfly was a very welcome surprise, and takes to nineteen, the number of species recorded on our garden pond.