As it is (ed: Not long past) Christmas, and I have already written of a
decidedly Christmassy species, I thought, in the dark of St Stephen’s Night, to
revisit the insects with which I spent a privileged summer, through the coastal
marshes of Essex. The Lestidae damselflies, or Emerald Damselflies, come in a
range of shades from key lime pie green, to metallic fir tree tinsel green,
some bearing a dusty blue pruinescence. They are desperately fashionable too,
subject of many treatises, management plans and UK Wildlife Podcasts, in part
because of their undoubted beauty, more subtle than that of the splendid Calopteryx
spp - perhaps more of them later- and less easily spotted than the big Aeshnids
I wrote about before. Essex is their spiritual home- and arguably one of the
epicentres of their remarkable colonisation of these islands. All four breeding
species are found in the county, and I had the privilege of meeting them all
over the summer of 2022.
 |
| Scarce Emerald Damselfly nomming a Blue Tailed Damselfly (Ishnura elegans) |
 |
| Willow Emerald Damselfy, RSPB Bowers' Marsh, Essex. |
My first encounter with these splendid creatures was a couple of years ago at
RSPB Rainham Marshes, where I met a gorgeous, deep bronze green insect hanging
serenely on some wetland tree that may or may not have been the one from which
it took its common name. This slim and delicate creature was a Willow Emerald (Chalcolestes
viridis) a stunning creature which immediately caught my eye, especially as
it was October, when all but the hardiest Common Darters and Migrant Hawkers had
reached the end of their season. The Willow Emerald is unique among British odonata
as it does not lay its eggs in water, but instead, in neat incisions made in
woody vegetation overhanging water with a modified ovipositor. I have witnessed
them laying eggs like this while still in tandem, the male gripping the female
with his anal claspers, protecting, or jealously guarding her. From these eggs
the tiny prolarvae emerge in spring, and drop into the water below to continue
their life cycle, much more typically. Any which fail to find water do not make
it, but conversely, being to an extent free of the need for water during late
summer oviposition offers an advantage in a drying climate. This species was first recorded breeding in
the UK in something like 2009, in Suffolk. On a September walk by the Thames at
Tilbury in 2022, with my good friend Chris, we found hundreds of these
beautiful, bronze green insects, hanging out on Brambles tens of metres from
fresh water. It is a species which has undergone a meteoric rise. Look for an
all-green Damselfly, sometimes shimmering bronze in the sunshine as the light
catches its iridescence, with clear wings (mind those flashy Calopteryx!)
white pterostigmas (the dots in the ‘outboard’ corners of the wings), hanging out
on marginal woody vegetation near still or slow-moving water.
 |
| Willow Emerald, Tilbury, September 2022 |
A few years later, while walking among the ditches at an EWT
nature reserve way off the beaten track yet not too far from Basildon. Hanging
on a branch, apparently relatively freshly emerged, was a beautiful male Scarce
Emerald (Lestes dryas). Contrary to its English name, this species seemed
very numerous on the sites where it lived. A hulking brute of a damselfly, size
being a key if not universally reliable way of separating it from the smaller
Emerald Damselfly (Lestes sponsa), and another species identified as having a
distinct upward population trend, it likes Sea Clubrush choked ditches, sometimes
to the consternation of site managers irked by its insistence on enjoying
exactly the habitats wading birds do not, and often co-occurs on the coastal
grazing marshes also favoured by Small-Red Eyed Damselflies and Ruddy Darter Damselflies.
Like all Odonata it is an active predator, adult and nymph, largely taking
small flies, but not averse to dining on
its distant relatives. At RSPB Old Hall, what I initially took to be a mating
pair of Blue-Tailed Damselflies, turned out on closer inspection to be a Scarce
Emerald feasting on the corpse of a Blue-Tailed Damselfly. In addition to an
impressive display of predation, though I had no way of telling whether the
Emerald had caught its prey on the wing or simply made a fortuitously (for the
Emerald) timed landing, it represented a good chance to compare the blue bits
of the two species. The steel blue pruinescence, a dusting of scales which fades
with age, contrasted strongly with the almost luminescent looking blue tail-light
of the commoner species. Scan through
the big crowds of Blue Tailed Damselflies for this big beast, and use your
close-focus bins or a good photo to identify it by the pruinescence covering
the whole of the first two segments of the abdomen, and the big, bent-paddle
claspers at the back end to separate from male Lestes sponsa. A slightly
different pattern of green and pale cream on the thorax separates the females
of these species. Look for them in June
and July, I saw few of them after the big heatwave of 2022, for reasons
unknown, perhaps it baked off the adults or desiccated any late developing nymphs.
 |
| Scarce Emerald (female) Essex 2022 |
 |
| Scarce Emerald (Male) Essex 2022 |
Historically, the commonest of the Lestidae in the British
Isles, and still the one you’re most likely to encounter outside of South
Eastern England, is Lestes sponsa, the Emerald Damselfly, you may hear
it called the Common Emerald Damselfly.
This species has undergone something of a decline of late, like many of
our odonata, as documented in the State of Britain’s Dragonflies report. It is
hard to separate from L. dryas, I recommend a good book with the illustrations
of Richard Lewington in it and a good pair of low-magnifying small binoculars
for close focus, though any particularly small Lestes-with-blue-bits is
likely to be one. Sadly I encountered just a few of this species during my summer
transects.
 |
| Emerald Damselfly, Essex, 2022 |
The fourth species is the newest, and perhaps the slowest colonising, the beautiful
and distinctive looking Southern Emerald Damselfly (Lestes barbarus).
This is a gorgeous, key lime pie of an insect, with its dark green metallic upper
surfaces contrasting with the pale, green-tinged yellow of its undersides,
boasting a unique and instantly recognisable (yes, really) bicolour pterostigma,
half milk white, half blackish brown. It has distinct ‘antehumeral stripes,’
look for markings like braces on its thorax. Its stronghold is on Canvey
Island, of all places, I am advised a particular ditch is a good place to look,
but I found it on the site near Basildon, where it was a new record. More
delicate looking than the other three, it was first recorded in Britain in 2002, in Norfolk, and it’s been gradually colonising low-lying
Essex since being discovered at Wat Tyler Country Park by Neil Phillips in July 2010, with other early records coming from Gunners Park, Shoeburyness in 2012. It is a
more committed climate change rebel, and habitat specialist, than even the
Willow Emerald, relying on ditches drying up in late summer for oviposition. I
could scarce believe my eyes when I found one near Basildon on an EWT reserve.
These species are moving so fast and unpredictably with their quiet invasion
that they are one group in which the observations of keen eyed amateur
naturalists and local surveyors can make real changes to known distribution
maps.
 |
| Southern Emerald Damselfly, EWT site, Essex. |
So think of them on these winter days, and dream of them shimmering beneath a
warm summer sky. Their season will roll around soon enough. Get yourself a good
dragonfly book, a good pair of bins, and, come June, go to your favourite
wetlands. You may just find yourself a new favourite insect there.
 |
| Southern Emerald Damselfly |
*This blog has been edited since posting to correct the timeline of Southern Emerald colonisation and credit the finder.
