Glasgow & SW Scotland Butterflies

Glasgow & SW Scotland Branch Website

February 13, 2011

Welsh Clearwing Surveys at Loch Rannoch 2011

Filed under: Moths — Andrew Masterman @ 3:29 pm

Welsh Clearwing is a spectacular moth which is a wasp-mimic and its UK stronghold is in Wales where it was first found at Llangollen in 1854.

Welsh Clearwing    Credit:  John Knowler

Welsh Clearwing Credit: John Knowler

Welsh Clearwing was first recorded in Scotland in the Rannoch area in 1867. There are scattered populations in Scotland: the Rannoch area; the Trossachs; Perth; and Glens Affric and Moriston.

Distribution of Welsh Clearwing in Scotland

Distribution of Welsh Clearwing in Scotland

Butterfly Conservation commissioned survey work in 2010 on rare moths in the Rannoch area  as part of the Moths Count project funded by the Heritage Lottery Fund and many other partner organisations. The results for Welsh Clearwing are presented below.

The easiest method of detecting Welsh Clearwing is by searching for exit holes on the south facing aspects of birch trunks. These exit holes which are created by the emerging adults can be numerous and may persist for many years. Searches for exit holes and pupal exuviae (the empty pupal cases which can sometimes be found protruding from the exit holes) increased the number of 1 km squares with Welsh Clearwing in the Rannoch area from seven to 16 which includes two new sites (Killichonan & Innerhadden) away from the previously one known site with Welsh Clearwing: Finnart on the south-west side of Loch Rannoch.

 

Three sites around Loch Rannoch where old Welsh Clearwing exit holes were found in 2010.

Three sites around Loch Rannoch where old Welsh Clearwing exit holes were found in 2010.

 

In Wales and Staffordshire, both Silver and Downy Birch are used (Graham, 2007) but in the Rannoch area, while both birch species are present, Welsh Clearwing exit holes were only found on Downy Birch. In the Trossachs too, Welsh Clearwing is only found on Downy Birch.

Aas and Riedmiller (1994) describe the bark of Downy Birch as “Red-brown at first, becoming greyish-white with brown or grey horizontal banding. Sometimes bark stays brownish even in large trees”. Their description of the bark of Silver Birch is “Shiny, reddish brown at first, later turning pinkish or white with pale grey horizontal markings and dark grey scales, with deep fissures and knobbly bumps towards base of tree”.  A Downy birch trunk riddled with Welsh Clearwing exit holes is shown below while Silver Birch trees tend to have larger crevices and are less horizontally banded.

Downy Birch trunk riddled with Welsh Clearwing exit holes.

Downy Birch trunk riddled with Welsh Clearwing exit holes.

Another difference between Silver and Downy Birch is the tree shape with Silver Birch generally being slender and taller up to 30 m high with branches angled sharply upwards and the outer branches curve downwards such that the foliage appears to elegantly cascade downwards. In contrast, Downy Birch are shorter up to 20 m tall with branches either angled upwards or more horizontal and they don’t curve downwards towards the tip giving the tree a much more compact and less attractive profile. However, both Silver and Downy Birch can hybridise with each other producing intermediate forms which are difficult to identify (Aas and Riedmiller,1994).

The two new sites with Welsh Clearwing exit holes present on Downy Birch trunks, Killichonan and Innerhadden, were discovered during nine random examinations of birch trees around Loch Rannoch. At one further site, only Downy Birch trees were found, but at the remaining six sites, only Silver Birch were present indicating that Silver Birch is dominant along large parts of the banks of Loch Rannoch.

Random sites around Loch Rannoch searched for Welsh Clearwing.

Random sites around Loch Rannoch searched for Welsh Clearwing.

 Given these results, it is unlikely that other new Welsh Clearwing sites will be found along the banks of Loch Rannoch but it is possible that Downy Birch may be present higher up the slopes above Loch Rannoch, so venturing away from the roadside might lead to new Welsh Clearwing sites. On the NBN gateway, there are two 10 km squares to the west of Loch Rannoch with historical Welsh Clearwing records (no specific details available) which need to be explored for presence of Downy Birch and Welsh Clearwing: NN35 and NN45.

Nine random sites around Loch Tummel were searched for Downy Birch and Welsh Clearwing but only Silver Birch trees were found so it is unlikely that Welsh Clearwing is present around Loch Tummel.

Raondom sites around Loch Tummel searched for Downy Birch and Welsh Clearwing.

Raondom sites around Loch Tummel searched for Downy Birch and Welsh Clearwing.

The map below shows the distribution of trees with Welsh Clearwing exit holes around Finnart found during survey work in 2010. New exit holes can be identified by their perfectly round shape and size (10 mm in diameter- see photo below) and fresh edges and a presence of a pupal exuvium (see photo below)  is also proof of occupancy by Welsh Clearwing in the current year. But in some of the 1 km squares below, only old exit holes were found which could mean that Welsh Clearwing is no longer present as these exit holes can persist from many years. Click here for a Word Document containing the Finnart map below which you can print out and take into the field.

Distribution of Downy Birch trees with Welsh Clearwing exit Holes at Finnart

Distribution of Downy Birch trees with Welsh Clearwing exit Holes at Finnart

A perfectly round fresh Welsh Clearwing exit hole.

A perfectly round fresh Welsh Clearwing exit hole.

A Welsh Clearwing pupal exuvium at Finnart on 30 June 2010

A Welsh Clearwing pupal exuvium at Finnart on 30 June 2010

Adult Welsh Clearwing are not easy to find (none found in 2010) but a Welsh Clearwing pheromone lure is available which makes finding adult Welsh Clearwing males easy in areas where they are present. This pheromone lure (termed SCO) can be pre-ordered before April from Anglian Lepidoptera Supplies and this is very effective at attracting male adult Welsh Clearwing during the flight period: late June to July.  Use of this pheromone lure is recommended for 2011 searches in those areas where only old exit holes were found in 2010. At Finnart, these are the following 1 km squares: NN5257; NN5455; NN5355: NN5224 and two further squares with birch woodland but which were not searched in 2010 need to be checked as well, NN5225 and NN5125.

A few new exit holes and one pupal exuvium were found at the first new site in 2010: Killichonan NN5556. At the second new site, Innerhadden, only old Welsh Clearwing exit holes were found so use of the pheromone lure is also required in square NN6657. The extent of this new site was not fully explored in 2010 so the 1 km squares either side also need exploring but it is suspected that these other squares only contain Silver Birch trees.  Click here for a Word Document containing the Innerhadden map below which you can print out and take into the field.

Welsh Clearwing exit holes present in Downy Birch at Innerhadden

Welsh Clearwing exit holes present in Downy Birch at Innerhadden

Welsh Clearwing is a rare moth only found locally at a few sites in Scotland (see Scottish Distribution map at the top of the page). However, it may be under-recorded to some extent, so if you visit the Rannoch area to familiarize yourself with the sort of open birch woodland it occupies and the appearance of the exit holes - trees with exit holes are common in areas in which Welsh Clearwing occurs  - you will be able to recognise potential new sites when you are out and about in the Highlands of Scotland.

References

Aas, G and Riedmiller, A. 1994. Trees of Britain and Europe. Collins Nature Guide.

Graham,A.N. 2007. Welsh Clearwing Synanthedon scoliaeformis on Berwyn, Montgomeryshire. CCW Contrct Science Report. Countryside Council for Wales, Bangor.

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