…written by Buglife Cymru, NaB Scarce Yellow Sally Conservation Officer Sarah Hawkes.
Join Buglife Cymru’s, Nature am Byth Scarce Yellow Sally Conservation Officer, Sarah, as she recounts her journey of discovery during this years’ survey season for her project; she shares some of the highs, the lows and some fascinating new discoveries! (part 1 of 2)
Wrexham’s rarest animal, Isogenus nubecula, the Scarce Yellow Sally, has emerged from the river waters for a brief 3-4 weeks as an adult stonefly. I’ve been tracking the emergence; counting exuvia (the cast skin left behind following an insect moult) on bridges and searching for sightings along the banks of the Welsh River Dee and keeping a brief record of my journey. Join me for the first half of the adventure.
Thursday 24 April 2025: I don’t suppose stoneflies will ever have the social media appeal of lambs, but Scarce Yellow Sally Stonefly surveying season is underway and along the River Dee we are beginning to see the adult flies, (longish dark coloured, about 2cm).
They are vanishingly rare and only occur in the UK on the Dee/Ceiriog in Wrexham County, so far as we know.
Nonetheless, I am going down to the Severn, near Welshpool for a look, just in case. Fingers crossed!
The best thing is, they are easiest to see on bridges and fence posts in the sunshine!
Friday 25 April 2025: The trip to the Severn with my Andrena bee expert friend Clare Boyes was an absolute delight, although in terms of stonefly finding all but fruitless.
I wanted to check out bridges for exuvia, left behind as the nymphs morphed into adults. Hoping a population of Scarce Yellow Sally might have been missed, we were trampling around riverbanks figuring out which bridges were accessible south of Welshpool.
We sort of knew the answer, but there is something about checking for yourself. The river at Berriew was beautiful and we had a lovely time wading about checking the walls for stoneflies.
We did find one live Brachyptera risi, Common February Red, and a Perlodes exuvia.
However, at bridges other than the Berriew bridge and aqueduct, invasive plants, Giant Hogweed, Japanese Knotweed and Himalayan Balsam, have taken a real hold and the Hogweed in particular makes the banks impenetrable.
Sunday 27 April 2025: On Friday I spent the morning at Bangor on Dee Bridge in the company of David Andrews, who wrote an early paper on finding Scarce Yellow Sally in the Dee, published in 1984.
I’d been down earlier and collected the remaining exuvia from the bridge; I found barely any had emerged over the preceding week, so they must have all but finished emerging from the river now.
We found Honeybees, Harlequin Ladybirds, Alder Beetles, hoverflies including one victim of a fungal attack, Yellow Dung Flies and a pretty little mayfly, called a Dusky Yellow Streak, but not a single stonefly over three hours.
It was a bit too windy perhaps? But I like to think we honed our technique for searching (!) We are sure they are there, we have the shed skins they emerged from…. but where?
We have talked to lots of people out for walks or a pint at the riverside pub; plenty of potential searchers who now have leaflets, which is a result.
We spent a fascinating morning together and I enjoyed tales of all things river related from David’s career looking at river; the pollution events that had run through the Dee over the years. From Phenol that caused the tap water to smell like ‘TCP antiseptic’, to a spill of whey
that killed hundreds of fish by causing bacterial blooms that used up all the oxygen in the river. It was so hard to identify because it wasn’t a toxin, as such, but a nutrient.
So many stories. Utterly fascinating and especially valuable to me, who only recently became involved seriously with stoneflies and the River Dee in the last two years.
Monday 28 April 2025: Hooray!!! We have found our first adult Scarce Yellow Sally stonefly this year! Alan from Chester Zoo Aquarium and I were hunting along the bank. I had found a Perlodes stonefly (which is slightly bigger and more common) when a “Sally” flew over and landed on my leg!
From that point on we found many in a small area and watched them landing on grasses, sometimes flying a little way. Watching and speculating about why they might be doing what they were doing kept us busy for a long time.
We also caught eight to record the ‘drumming’ they do to call each other.
In itself that was a bit of an adventure; I managed to put two into a tube together that were opposite sexes – not the plan in case the ensuing mating put them out of the mood for drumming!
Having caught them I was left with a bit of a problem. I had not been able to bear the thought of ordering empty cardboard boxes online for some extortionate sum each, so had nothing ready as a recording studio.
On the way home I stopped at “Stans” to look, thinking perhaps of large match boxes. Happily, as I walked in there was a pile of mini cereals packs on offer, perfect size and food grade clean so safe for “Sallys” to live in for a night or two before going back to the river!!
With the recorder set up and the “Sallys” drumming (not as exciting as it sounds, a few, up to six, quiet taps now and again) I had the recording I wanted.
I am left with eight little packs of cereal and have a stonefly sound studio set up – win win!
Join us for Part two of Sarah’s mini-journal on Wednesday 9 July.
What can you do to help…?
If Sarah’s mini journal has piqued your interest and you want to get involved in our Scarce Yellow Sally project, please do get in touch. We are particularly interested in help between April and June, when we are asking the public to help us locate, photograph and report any sightings of stoneflies along rivers in Wales. But it is likely that sightings outside of these times are of interest too particularly given Sarah’s experience with the Wrexham University students this year.
If you live outside of the project area but think you may have found a Scarce Yellow Sally, please record your sighting via our Search for the Scarce Yellow Sally web form too.
Main Image Credit: Scarce Yellow Sally (Isogenus nubecula) © Sarah Hawkes