Saturday, 21 July 2018

Event report: Welsh Clearwing afternoon at Lake Vyrnwy

The Afon Nadroedd valley
Last Saturday we departed from our usual evening event format to hold a daytime event, in the picturesque Afon Nadroedd valley just north of Lake Vyrnwy. Hopes were high as the emphasis was on finding the Welsh Clearwing, a nationally important Red Data Book species. Most of those attending the event had never seen any species of Clearwing, and were optimistic that Douglas' pheremone lures would have the desired effect.

The weather was very warm and dry, as it has been for several weeks now, and fifteen optimistic moth-ers congregated beneath a large sycamore beside the Nadroedd stream, enjoying a shady picnic spot before the serious searching began.

The recently purchased MMG butterfly nets proved popular, and there was much sweeping along the roadside and over the extensive marshy area. Peter lost count of the number of Agriphila straminella he netted, but declared he'd be a wealthy man if he had three- halfpence a moth!

Old emergence holes
It was good to meet Andrew Graham, butterfly and moth recorder for Merionethshire and Anglesey, and also butterfly recorder for Caernarvonshire. He explained that the Welsh Clearwing is rare in North Wales, and reliant on old Downy or Silver Birch trees with exposed lower trunks, such as those to be found alongside the lane we were exploring. His online database, North Wales Lepidoptera, describes the life cycle fully, and explains that the larvae feed on the inner bark for several years. When fully grown they tunnel to just under the surface of the bark, construct a cocoon out of frass granules, and then pupate within it. When ready to emerge, the outer end of the cocoon is neatly severed and a wriggling motion enables the pupa to move outwards until partially exposed to the atmosphere. Interestingly, backward pointing spines on the pupa ensure that only forward movement is possible. The adult moth then emerges from the pupa, often leaving the pupal case (exuvia) remaining in the emergence hole.

A hopeful crowd formed around the pheromone lure
Because this is a scarce species, every occupied birch is important, and Douglas set up pheromone lures in trees where the species has been located in the past, as the adult male moth responds well to this technique. As the sun shone, and we were within the expected flight period, we remained hopeful, although the last positive record from this site was in 2012, when two exuviae and a fresh cocoon were recorded. We were able to see the tell-tale 5mm circular emergence holes though, which remain visible for many years, and also observed the larval tunnels in places where some of the surface bark was missing. But despite our perseverance, there was no evidence of either the moth or a fresh emergence.

Scalloped Hook-tip
However, there were a few other day-flying macro moths to be seen, including several Silver Y, a Barred Straw, and a Straw Dot. Two more micro moths, Celypha lacunanna and Scoparia ambigualis were recorded. It was also a chance to look for larvae, and the distinctive green and yellow striped caterpillar discovered on bracken was identified as Broom Moth. Shortly afterwards, a caterpillar closely resembling a birch catkin was found on a birch and identified as a Scalloped Hook-tip. A tiny 'looper' caterpillar was collected by Douglas when beating but has yet to be identified.

Butterfly species were predictably more numerous than moths, and a pristine Small Copper was much admired. Ringlets were common, as were Green-veined Whites and Small Heath. Also flying were Meadow Browns, Large Whites and a Large Skipper. A Small Tortoiseshell and Red Admiral put in an appearance as well.

Several minutes were spent trying to photograph dragonflies over and around the stream. Mark managed to capture on camera what he identified as a Golden-ringed Dragonfly, although it eluded the rest of us.

Other eye-catching invertebrates included a large and conspicuous orbweb spider with a distinctively patterned globular abdomen, and a Forest Bug.

Despite drawing a blank as far as seeing Welsh Clearwings went, it was an interesting afternoon enjoyed by all - and if another daytime event is planned, no doubt there will be plenty of attendees. As people prepared to head for home, a group of ponies grazing the hill came down to the stream to drink, as if to see us off!

Thanks to Douglas for organising the event, and for adding another moth to our rather short list - A Small Seraphim which found its way into his car and travelled home with him!

Sue S.

The species list can be found here. And all the photos from the afternoon at the link below:
MMG event: Welsh Clearwing(less) afternoon -14/07/18

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