At a glance
Ancient alkaline fen NNR in central Anglesey — southern marsh orchids, fen orchid, fen sedges, dragonflies (15+ species), water voles, and specialist fen invertebrates in one of Wales's rarest habitats. Boardwalk paths, free, Natural Resources Wales. Best June–July (orchids) and July–September (dragonflies). 4 miles from Llangefni. LL75 8PR.
About Cors Bodeilio
Cors Bodeilio is a National Nature Reserve in the agricultural interior of Anglesey — an ancient alkaline fen that represents one of the rarest habitats in Wales. Alkaline fens (rich fens or carr) develop over deep peat in areas with calcareous groundwater, and most of those that once covered lowland Anglesey and Britain more generally have been destroyed by agricultural drainage. Cors Bodeilio survives as a fragment of what the island's wetland interior looked like before intensive farming, and its botanical and invertebrate communities are of national importance.
The headline species are orchids: southern marsh orchid, common spotted orchid, early marsh orchid, and the rare fen orchid all occur here (May–July peak). The fen sedge communities support specialist invertebrates — hoverflies, beetles, and moths found almost nowhere else in Wales. Dragonflies abound in summer over the open water and ditches (up to 15 species). Water voles inhabit the ditches. Boardwalk paths allow visitors to enter the fen without damaging the habitat; the NRW car park is small and unsigned from main roads, making this genuinely one of Anglesey's least-visited nature reserves.
The reserve is approximately 4 miles east of Llangefni on the B5109. Oriel Môn (Llangefni, free) and Llyn Alaw reservoir (5 miles, birdwatching) combine naturally for a full central Anglesey day.
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Frequently asked questions
Cors Bodeilio (the name means "Bodeilio's Marsh" in Welsh) is a National Nature Reserve on Anglesey, managed by Natural Resources Wales, occupying an ancient alkaline fen in the agricultural interior of the island near Llangefni. It is one of the best examples of alkaline fen (also called rich fen or carr) in Wales — a wetland habitat that develops over deep peat in areas with mineral-rich, calcareous groundwater. This habitat has become exceptionally rare throughout Britain as drainage for agriculture has destroyed most of the ancient fens that once covered large parts of the lowland landscape. Cors Bodeilio is one of the surviving fragments, and its rich botanical and invertebrate communities reflect what much of lowland Anglesey would have looked like before intensive agricultural improvement.
Cors Bodeilio has an exceptionally rich flora driven by the alkaline groundwater. Orchids are the headline species: southern marsh orchid, common spotted orchid, early marsh orchid, and the rare fen orchid (one of Wales's rarest plants) all occur here. The fen sedge communities — with tall stands of great fen sedge, tufted sedge, and bladder sedge — are characteristic of the habitat and support rare fen invertebrates including specialist hoverflies, beetles, and moths associated with this declining habitat type. The open water areas and ditches hold water voles (now rare in Wales), and dragonflies are abundant in summer (up to 15 species have been recorded). Bitterns have wintered here occasionally. The fen birch and willow carr around the margins gives additional structural diversity. Botanists find Cors Bodeilio one of the most rewarding sites in north Wales; for general visitors, the orchid season (May–July) gives the most accessible visual impact.
The orchid season (late May through July) is the best time for a botanical visit — the southern marsh orchid and common spotted orchid are typically at their peak in June, and the fen orchid (if present) flowers slightly later. Dragonflies are most active from July to September — the open water and reed beds on warm afternoons can have impressive numbers of species. For birdwatching, spring (April–June) gives breeding warblers in the fen carr and reed beds; winter occasionally produces water rail, snipe, and occasionally bittern in the ditches. The boardwalk paths may be flooded or slippery in winter and early spring — rubber boots are advisable from October to April. The reserve is small enough (a few tens of hectares) that the main features can be seen in a single visit of 45–90 minutes; botanists and entomologists will want longer.
Cors Bodeilio is in the rural interior of Anglesey and is not signposted from the main roads in a way that makes it easy to find by chance. The reserve is accessed from a small NRW car park off the B5109 road between Llangefni and Pentraeth, approximately 4 miles east of Llangefni. The coordinates (LL75 8PR) give a reasonable approach point by GPS or map. Without navigation, the reserve can be difficult to locate on a first visit; it is worth downloading the NRW location information or checking a detailed map before travelling. The reserve is emphatically not a tourist attraction in the conventional sense — it has no visitor centre, no café, no signage visible from the main road, and no staff on site. It is a genuine nature reserve for people who specifically want to see the fen habitat and its associated plants and animals.
Anglesey has a notable concentration of nationally important nature reserves. Newborough Warren NNR (south-west Anglesey) is one of the largest dune systems in Wales, with rare dune plants and a large colony of natterjack toads (though toad populations have declined). Cemlyn Bay (north Anglesey, covered in detail in our wildlife section) has the largest tern colony in Wales. Cors Ddyga (near Llangefni) is a wetland NNR adjacent to Cefni Reservoir with good birdwatching. Llyn Alaw reservoir (north-central Anglesey) has waders and wildfowl. The Anglesey AONB coastline includes several important coastal nature reserves. Puffin Island (Ynys Seiriol, off Penmon Point) is a Seabird Colony SSSI with breeding guillemots, razorbills, cormorants, and puffins. Red squirrel conservation areas across the island include Newborough Forest. Anglesey is, for its size, one of the most wildlife-rich islands in Britain.