Caeau Bwlch

Site of Special Scientific Interest · 52.8089, -4.0915

Geology & landscape

Geological Period: Cambrian · Rock Type: Glacial Till

Landscape processes: Glacial

Description

Description Caeau Bwlch is of special interest for its populations of hornet robberfly Asilus crabroniformis. The site comprises a series of small, predominantly west-facing, cattle-grazed pastures on gently sloping ground, 0.5 to 1.5km south-east of the village of Llanbedr at an altitude of 80-120m. The underlying geology is dominated by mudstones, siltstones and sandstones of the Lower Cambrian Llanbedr Formation which is overlain by a veneer of unconsolidated glacial till and well-drained, coarse, loamy soils. The vegetation of this site is mainly semi-improved grassland. However there are some areas of relatively unimproved neutral grassland, where species such as crested dogstail Cynosurus cristatus, common birds-foot trefoil Lotus corniculatus, bulbous buttercup Ranunculus bulbosus are found. In some parts of these less improved areas there are species such as heath grass Danthonia decumbens and harebell Campanula rotundifolia which suggest slightly more acidic soils. Waxcap Hygrocybe fungi are also frequent in the less improved fields. Many of the pastures support large stands of bracken particularly around the field boundaries and there is localised scrub including hawthorn Crataegus monogyna, blackthorn Prunus spinosa and gorse Ulex europaeus. Pastures in the easternmost part of the site support broad-leaved wooded copses dominated by sessile oak Quercus petraea. The site supports one or more populations of hornet robberfly Asilus crabroniformis, a rare species of fly which was first recorded here in 1992. This is one of the most important sites for the species in Wales and is currently one of only two known sites in north-west Wales. Adult robberflies have been observed feeding on small dung beetles such as Rhodaphodius foetens and Teuchestes fossor. Female hornet robberflies are known to oviposit on decaying cow dung. The maintenance of populations may therefore be dependent upon a continuation of low intensity cattle grazing, particularly just prior to and during the adult flight period from mid July to early October. Scrub and bracken on the site appear to provide suitable roosting stations for adult robberflies. Remarks: The hornet robberfly is a UK BAP Priority Species The site lies with the Snowdonia National Park

Species mentioned

English name
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Latin name
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IUCN / Red List Type Family
dung beetle Rhodaphodius foetens LC beetle scarabaeidae
no common name Teuchestes fossor LC beetle chafers scarabaeidae
crested dog's tail Cynosurus cristatus LC grass poaceae
heath grass Danthonia decumbens NT grass poaceae
harebell Campanula rotundifolia LC herb campanulaceae
birdsfoot trefoil Lotus corniculatus LC herb fabaceae
bulbous buttercup Ranunculus bulbosus LC herb ranunculaceae
hawthorn Crataegus monogyna LC shrub rosaceae
blackthorn Prunus spinosa LC shrub rosaceae
gorse Ulex europaeus LC shrub leguminosae
sessile or durmast oak Quercus petraea LC tree fagaceae

Insects to look out for

These moths, butterflies and beetles are known to feed on plants recorded at this site, and carry a notable UK conservation status — but a host-plant being present doesn't mean the insect has actually been recorded here. Treat this as "worth watching for," not a confirmed sighting.

SpeciesStatusVia host-plant
Black-veined moth
Siona lineata
Critically Endangered Lotus corniculatus
New forest
Zygaena viciae
Critically Endangered Lotus corniculatus
Straw belle
Aspitates gilvaria
Endangered Lotus corniculatus
Oak lutestring
Cymatophorina diluta
Endangered Quercus petraea
Figure of eight
Diloba caeruleocephala
Endangered Crataegus spp., Prunus spinosa, Prunus spp.
The lappet
Gastropacha quercifolia
Endangered Crataegus monogyna, Prunus spinosa, Prunus spp.
Wood white
Leptidea sinapis
Endangered Lotus corniculatus
Scarce vapourer
Orgyia recens
Endangered Crataegus spp., Prunus spinosa, Quercus spp.
Black hairstreak
Satyrium pruni
Endangered Prunus spinosa
Slender scotch
Zygaena loti
Endangered Lotus corniculatus
Mouse moth
Amphipyra tragopoginis
Vulnerable Crataegus spp., Lotus corniculatus
The sprawler
Asteroscopus sphinx
Vulnerable Crataegus spp., Prunus spinosa, Prunus spp., Quercus spp.
Mottled umber
Erannis defoliaria
Vulnerable Crataegus spp., Prunus spinosa, Quercus spp.
Dingy skipper
Erynnis tages
Vulnerable Lotus corniculatus
The lackey
Malacosoma neustria
Vulnerable Crataegus monogyna, Prunus spinosa, Prunus spp., Quercus spp.
Pale brindled
Phigalia pilosaria
Vulnerable Crataegus monogyna, Prunus spinosa, Quercus spp.
Silver studded blue
Plebejus argus
Vulnerable Lotus corniculatus, Ulex spp.
Lead belle
Scotopteryx mucronata
Vulnerable Ulex europaeus
Brown hairstreak
Thecla betulae
Vulnerable Prunus spinosa
Early moth
Theria primaria
Vulnerable Crataegus monogyna, Prunus spinosa, Quercus spp.
Pale eggar
Trichiura crataegi
Vulnerable Crataegus monogyna, Prunus spinosa, Quercus spp.
Oak hook-tip
Watsonalla binaria
Vulnerable Quercus petraea
Flounced chestnut
Agrochola helvola
Near Threatened Crataegus monogyna, Quercus spp.
Beaded chestnut
Agrochola lychnidis
Near Threatened Crataegus monogyna, Ranunculus spp.
Grey chi
Antitype chi
Near Threatened Crataegus monogyna
Garden tiger
Arctia caja
Near Threatened Prunus spinosa
Small heath
Coenonympha pamphilus
Near Threatened Cynosurus cristatus
Large thorn
Ennomos autumnaria
Near Threatened Crataegus spp., Prunus spinosa, Prunus spp., Quercus spp.
September thorn
Ennomos erosaria
Near Threatened Quercus spp.
Grey pug
Eupithecia subfuscata
Near Threatened Crataegus monogyna, Prunus spinosa
Double dart
Graphiphora augur
Near Threatened Crataegus spp., Prunus spinosa, Quercus spp.
Clay fan-foot
Paracolax tristalis
Near Threatened Quercus spp.
Frosted green
Polyploca ridens
Near Threatened Quercus petraea

Host-plant data: Cook et al. (2025), Traits data for the butterflies and macro-moths of Great Britain and Ireland, 2024, UK Centre for Ecology & Hydrology / Butterfly Conservation; and Padovani et al. (2020), Database of Insects and their Food Plants (DBIF), UK Centre for Ecology & Hydrology (both Open Government Licence). Contains data supplied by UK Centre for Ecology & Hydrology.

Plant communities

W25 — Bracken scrub

Pteridium aquilinum-Rubus fruticosus underscrub

Matches 3 species from the description above: Crataegus monogyna, Prunus spinosa, Ulex europaeus

Hedera helix, Acer pseudoplatanus, Fagus sylvatica, Quercus robur, Fraxinus excelsior, Sambucus nigra, Ulex europaeus, Crataegus monogyna, Prunus spinosa, Luzula multiflora, Mnium hornum, Brachythecium rutabulum, Kindbergia praelonga, Angelica sylvestris, Conopodium majus, Heracleum sphondylium, Arum maculatum, Cirsium arvense, Lonicera periclymenum, Silene dioica, Stellaria holostea, Mercurialis perennis, Geranium robertianum, Glechoma hederacea, Teucrium scorodonia, Hyacinthoides non-scripta, Chamerion angustifolium, Circaea lutetiana, Digitalis purpurea, Rumex acetosa, Anemone nemorosa, Ficaria verna, Potentilla erecta, Rosa arvensis, Rosa canina, Rubus fruticosus agg., Rubus idaeus, Galium aparine, Galium mollugo sens.lat., Galium saxatile, Urtica dioica, Viola riviniana, Agrostis capillaris, Anthoxanthum odoratum, Arrhenatherum elatius, Dactylis glomerata, Festuca rubra, Holcus lanatus, Holcus mollis, Poa trivialis, Pteridium aquilinum, Dryopteris dilatata, Dryopteris filix-mas

W21 — Hedgerow scrub, Mixed scrub

Crataegus monogyna-Hedera helix scrub

Matches 2 species from the description above: Crataegus monogyna, Prunus spinosa

Hedera helix, Salix cinerea, Acer pseudoplatanus, Ilex aquifolium, Betula pendula, Corylus avellana, Fagus sylvatica, Quercus robur, Fraxinus excelsior, Malus sylvestris, Sorbus aria, Taxus baccata, Ulmus glabra, Ulmus procera, Sambucus nigra, Viburnum lantana, Euonymus europaeus, Cornus sanguinea, Juniperus communis, Ligustrum vulgare, Clematis vitalba, Rhamnus cathartica, Crataegus laevigata, Crataegus monogyna, Prunus spinosa, Juncus effusus, Plagiomnium undulatum, Brachythecium rutabulum, Kindbergia praelonga, Rhynchostegium confertum, Tamus communis, Heracleum sphondylium, Torilis japonica, Arum maculatum, Arctium minus, Cirsium arvense, Lonicera periclymenum, Moehringia trinervia, Silene dioica, Stellaria graminea, Stellaria holostea, Stellaria media agg., Calystegia sepium, Mercurialis perennis, Geranium robertianum, Iris foetidissima, Glechoma hederacea, Lamium purpureum, Origanum vulgare, Stachys sylvatica, Teucrium scorodonia, Allium ursinum, Hyacinthoides non-scripta, Circaea lutetiana, Rumex sanguineus, Anemone nemorosa, Ranunculus repens, Fragaria vesca, Geum urbanum, Potentilla sterilis, Poterium sanguisorba, Rosa arvensis, Rosa canina, Rubia peregrina, Rubus fruticosus agg., Galium aparine, Urtica dioica, Viola riviniana, Anisantha sterilis, Arrhenatherum elatius, Brachypodium pinnatum, Brachypodium sylvaticum, Bromopsis erecta, Dactylis glomerata, Elytrigia repens, Holcus lanatus, Holcus mollis, Poa trivialis, Asplenium scolopendrium, Pteridium aquilinum, Dryopteris filix-mas

W22 — Hedgerow scrub, Mixed scrub

Prunus spinosa-Rubus fruticosus scrub

Matches 2 species from the description above: Prunus spinosa, Ulex europaeus

Hedera helix, Acer campestre, Corylus avellana, Ulex europaeus, Prunus spinosa, Plagiomnium undulatum, Brachythecium rutabulum, Eurhynchium striatum, Kindbergia praelonga, Thuidium tamariscinum, Atrichum undulatum, Lophocolea bidentata, Achillea millefolium, Cardamine flexuosa, Lonicera periclymenum, Moehringia trinervia, Silene dioica, Silene uniflora, Stellaria media agg., Mercurialis perennis, Geranium robertianum, Stachys sylvatica, Teucrium scorodonia, Hyacinthoides non-scripta, Oxalis acetosella, Digitalis purpurea, Plantago lanceolata, Veronica chamaedrys, Armeria maritima, Rumex acetosa, Filipendula ulmaria, Geum urbanum, Rosa canina, Rubus fruticosus agg., Rubus idaeus, Galium aparine, Urtica dioica, Viola riviniana, Agrostis capillaris, Brachypodium sylvaticum, Dactylis glomerata, Festuca rubra, Holcus lanatus, Holcus mollis, Poa trivialis, Asplenium scolopendrium, Pteridium aquilinum, Dryopteris borreri, Dryopteris filix-mas

W20 — Montane scrub

Salix lapponum-Luzula sylvatica scrub

Matches 1 species from the description above: Campanula rotundifolia

Salix arbuscula, Salix cinerea, Salix lapponum, Salix myrsinites, Salix phylicifolia, Salix reticulata, Empetrum nigrum, Calluna vulgaris, Salix lanata, Vaccinium myrtillus, Vaccinium uliginosum, Carex atrata, Carex bigelowii, Carex binervis, Carex flacca, Luzula multiflora, Luzula sylvatica, Huperzia selago, Selaginella selaginoides, Aulacomnium palustre, Mnium hornum, Philonotis fontana, Plagiomnium undulatum, Rhizomnium punctatum, Dicranum bonjeanii, Dicranum majus, Dicranum scoparium, Fissidens adianthoides, Racomitrium lanuginosum, Calliergonell cuspidatum, Ctenidium molluscum, Hylocomium splendens, Hypnum callichroum, Hypnum cupressiforme, Palustriella commutatum, Plagiothecium denticulatum, Plagiothecium undulatum, Pleurozium schreberi, Ptilium crista-castrensis, Rhytidiadelphus loreus, Rhytidiadelphus squarrosus, Rhytidiadelphus triquetrus, Sanionia uncinata, Scorpidium revolvens, Thuidium tamariscinum, Atrichum undulatum, Polytrichastrum alpinum, Sphagnum capillifolium, Sphagnum fallax, Sphagnum girgensohnii, Sphagnum palustre, Sphagnum russowii, Sphagnum squarrosum, Sphagnum subnitens, Sphagnum teres, Barbilophozia barbata, Chiloscyphus polyanthos, Diplophyllum albicans, Lophocolea bidentata, Plagiochila porelloides, Ptilidium ciliare, Scapania undulata, Cladonia squamosa, Peltigera canina, Angelica sylvestris, Caltha palustris, Hieraclium spp., Saussurea alpina, Solidago virgaurea, Campanula rotundifolia, Succisa pratensis, Valeriana officinalis, Rhodiola rosea, Vaccinium vitis-idaea, Thymus praecox, Epilobium anagallidifolium, Dactylorhiza viridis, Euphrasia officinalis, Rhinanthus minor, Oxalis acetosella, Oxyria digyna, Polygonum viviparum, Rumex acetosa, Anemone nemorosa, Ranunculus acris, Thalictrum alpinum, Alchemilla alpina, Alchemilla glabra, Filipendula ulmaria, Geum rivale, Galium boreale, Galium saxatile, Saxifraga aizoides, Saxifraga hypnoides, Saxifraga oppositifolia, Saxifraga stellaris, Viola riviniana, Agrostis canina, Agrostis capillaris, Anthoxanthum odoratum, Deschampsia cespitosa, Deschampsia flexuosa, Festuca ovina, Festuca rubra, Nardus stricta, Dryopteris dilatata, Phegopteris connectilis