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Eyarth Rocks Reserve with inset of Pearl-bordered Fritillary

Eyarth Rocks Reserve with inset of Pearl-bordered Fritillary

Jan Miller

Eyarth Rocks Butterfly Conservation Reserve

The Eyarth Rocks reserve is part of Craig-adwy-wynt (Welsh for 'windy ridge'), which lies between the villages of Llanfair DC and Pwll Glas, about two miles south of Ruthin. It is one of the richest butterfly sites in North Wales: - 32 of the 34 species known to occur in the region have been recorded on this limestone hill-top. The national charity Butterfly Conservation completed the purchase of this important new reserve in 2001. Twenty acres of this Site of Special Scientific Interest have so far been secured as Butterfly Conservation’s second nature reserve in Wales and its first in the north of the country.

To reach the reserve make first for Ruthin (turn off the A55 for Mold). Take the Bala road out of Ruthin for about 2 miles. Just before the village sign for Pwll Glas take the left turning signed Llanfair D.C. Immediately over the stone bridge is a layby where there is parking for about 4 cars (do not obstruct the field gate.) Grid Reference; SJ 127553. Follow the public footpath from the corner on the opposite side of this lane, along the old railway line. (Don't confuse this path with the one for the North Wales Wildlife reserve which is on the other side of the main road you have just turned off.) The path is short but quite steep and good walking footwear is recommended. At the stile cross the field along the right side to the stile near the house. Cross the lane and follow the footpath up behind the house. This path goes through woodland and comes out at a gate at the northern end of the reserve.

The cap of the ridge is ‘limestone pavement ’ , a distinctive worn and fissured type of dense, hard  limestone that is one of Britain’s rarest habitats. The majority of this habitat in the British Isles is found in the Yorkshire Dales, Cumbria and north Lancashire, where the Carboniferous limestone was scoured by glaciers during the last ice-age. There are only a couple of limestone pavement sites in Wales and this ridge is of particular importance for the extent and quality of the habitat. This importance is demonstrated by the Site of Special Scientific Interest designation that applies to the ridge and adjoining areas of ancient woodland .

The pavement’s clints and grikes, formed by post-glacial weathering, make them of great interest as geological features. These fissures, pits and hollows in the rock provide a varied topography and special micro-habitats. This results in a distinctive plant community where limestone calciolous grassland with abundant mosses and lichens, occurs alongside woodland species and those indicative of the acidic soils derived from pockets of decayed vegetation. Bloody cranesbill, ( Geranium sanguineum ) Hound’s Tongue ( Cynoglossum officinale ), Mountain melick ( Melica nutans ) and Moonwort ( Botrychium lunaria ) are amongst the most notable and distinctive species present. Yellow archangel,( Lamiastrum galeogdolon) Dog’s mercury ( Mercurialis perennis ) , woodruff (Galium odoratum) , wood sorrel ( Oxalis acetosella ), Harts-tongue fern ( Phillitis scolopendria ) and Sanicle ( Sanicula europara ) are normally all indicators of ancient woodland sites and demonstrate how long the clints and grikes have been providing them with moist sheltered conditions.

The main reason for acquiring the reserve is the importance of the Craig-adwy-wynt ridge for the Pearl-bordered Fritillary ( Boloria euphrosyne ). This butterfly has declined so much throughout the UK that the population on this ridge is now one of the most important of those known to remain in Wales. Only 17 sites for the species were located in the 1997 UK survey, the species has since disappeared on some of them and Craig-adwy-wynt is one of the few that can be considered a ‘stronghold’. The bare rock and bracken litter with abundant violets make the site’s habitats particularly suitable for this butterfly’s warmth-needing caterpillars. There is a delicate balance needed between the bracken and the violets for the Fritillaries to thrive. The larvae of Pearl-bordered Fritillary usually feeds only on the Common Dog Violet (Viola riviniana), whilst those of the  Small Pearl-bordered ( Boloria selene ) and Dark Green Fritillary ( Argynnis aglaja ) generally use a wider selection of violets including Marsh violet (Viola palustris) and Hairy violet (Viola hirta) . Research by the Society has shown that the shelter of the growing bracken in April, plus up to 15cms.of the dead plant litter from previous years, raises the temperature around the violets by as much as 15 to 20 degrees above ambient air temperature. The Pearl-bordered Fritillary emerges earlier than most other species from its hibernation as larvae in the litter , so it needs this extra warmth early in the season. The litter provides them with ideal basking surfaces and to a point suppresses most other plant growth apart from violets. However, if the bracken litter gets too deep even the violets can disappear. The presence of suitable nectar sources such as early flowering species like Bugle (Ajuga reptans) and Wood Sage (Teucrium scorodonia) also characterises good Pearl-bordered Fritillary sites. Thus management of such sites is difficult to get right. Experiments are being carried out by volunteers in strimming and then raking bracken litter from controlled patches and monitoring the re-growth of both bracken and violets, plus monitoring their usage by egg-laying female butterflies. This will be a long term project to determine the optimum number of years rotation of such bracken control.

The rapid changes in agriculture and woodland management that occurred during the 20th. century have had a serious impact on this species. Sedentary in its habits, but nevertheless with the capability of colonising over distances of a few miles, it was well adapted to the habitat created by earlier woodland management practices. Its bracken habitat would have been patchy in its suitability, or availability being both controlled and cropped such as for stock bedding. Since WWII the shift to large scale afforestation with conifers, the reduction in regular ride opening and creation of other clearings, and the removal or abandonment of bracken areas, have all taken a toll on the habitat available to this butterfly an others.

Other important species also occur on the site. They are not as threatened as the Pearl-bordered Fritillary, but nevertheless are in need of conservation measures. These include Dingy Skipper (Erynnis tages), Grizzled Skipper (Pyrgus malvae), Small Pearl-bordered Fritillary, Grayling and Brown Argus (Aricia agestis) , each of which has quite specialised habitat requirements. With its areas of flowery grassland that warm-up rapidly because of the thin soils, exposed rocks and sheltering scrub, Craig-adwy-wynt provides the sort of specialised habitat that these species, and many others thrive on.

Orchids growing across the site include Twayblade ( Listera ovata) , Butterfly orchid ( Platanthera chlorantha ) and Early purple (Orchis mascula) . There are also some specimens of the rare Welsh Yew; The North Wales Wildlife Trust reserve on the opposite side of the road through Pwll Glas has larger numbers of both the Yew and native orchids.

Butterfly Conservation volunteers in North-east Wales as well as from the Wirral and Cheshire, have already put an enormous effort into scrub management on the reserve the last four winters.  The results are excellent, already showing a six-fold increase in the numbers of Pearl-bordered Fritillary counted on site, as well as the return of Dingy Skipper and Grayling that have been absent for many years. But more needs to be done and the aim is to reinstate a suitable grazing regime that will help make the task of controlling scrub growth much easier. For this the site’s boundary walls and fences need to be repaired, which will require considerable expenditure provided by an Objective One grant from the EU. Local members of the small North Wales Branch of Butterfly Conservation have been raising funds and doing the physical work on the reserve, and more volunteers are always very welcome. Volunteers to classify the many species of mosses, lichens, fungi and other specialists of this unusual habitat would also be very welcome.

A bilingual guide leaflet to the reserve is now available from

For further information please contact:

Jan Miller; e-mail ;

Rob Whitehead; e-mail; or

Butterfly Conservation Wales office; Swansea: 0870 770 6153 e-mail;

September 05, 2005 change by giorgio

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Jan Miller

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To find out when the next Butterfly Conservation local branch guided walk is to this or other rare butterfly sites, or to go moth-trapping in North Wales visit the events page on or e-mail to be added to our mailing list.

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address:Pensychnant Conservation centre

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