The Large Heath, now considered extinct in Cornwall, was bound to Common and Hare’s-tail Cotton Grass in intact peat bogs. Its return would require re-wetted, open bogs, region-wide cooperation, and years of patient monitoring before this delicate summer presence could flutter again.
In the upland bogs of Cornwall, summer once carried a quiet flutter. The Large Heath butterfly (Coenonympha tullia) moved with an unhurried, bobbing flight over pools of Sphagnum moss and swathes of cotton grass, its wings never opening in rest. Today, confirmed sightings have not been recorded for decades. Occasional recent reports remain unverified, and most authorities now consider the butterfly extinct—or functionally so—in Cornwall. Yet the story of this species is inseparable from the health of the county’s bogs, and to understand one is to understand the other.
Small to medium in size, with a wingspan of 41–45mm, the Large Heath is easy to miss if you are not looking. Its mottled brown-grey undersides are marked with small ringed eyespots that vary subtly from place to place. It is easily confused with the Small Heath, but its larger size and exclusive reliance on wet bog habitat set it apart.
Historically, Cornwall’s upland blanket bogs, wet heaths, and acidic moorlands held scattered colonies. These habitats are defined by deep peat soils, a persistently high water table, and a patchwork of moss, sedge, and low heath vegetation. The butterfly’s presence here was more than aesthetic—it was an ecological indicator that the bog was intact and thriving.
The Large Heath’s life cycle turns on a single plant group: cotton grasses. Chief among them in Cornwall is Common Cotton Grass (Eriophorum angustifolium), but Hare’s-tail Cotton Grass (E. vaginatum) is also used where present.
From late May into June, their pale, wind-tossed seed heads rise above the bog, signalling the start of the butterfly’s flight season.
The synchrony between cotton grass flowering and butterfly emergence is critical. A well-timed bloom means shelter, basking spots, and fresh food for larvae. A mismatch—caused by drought, cold snaps, or other disruptions—can shorten the breeding window and reduce survival.
For the Large Heath to survive in Cornwall, several conditions would need to align:
Cornwall’s bogs shift with the seasons, and these changes set the terms for the butterfly’s survival.
Good years for the Large Heath are marked by timely rainfall, lush cotton grass, and minimal disturbance. Poor years can lead to sharp population crashes.
Opening and maintaining bog habitats is central to the butterfly’s conservation. Blocking drains and re-wetting sites revives cotton grass beds and Sphagnum cover. Removing shading scrub restores the open structure, while light, controlled grazing prevents overgrowth without damaging plants.
Research from UK peatland restoration projects suggests that near-optimal butterfly numbers occur when cotton grass cover is high—around 57 percent in successful reintroduction trials—with cross-leaved heath adding further benefit. Well-managed bogs can recover quickly, but recolonisation—if it happens—will be slow.
Restoration needs multi-year monitoring and region-wide cooperation among landowners, conservation agencies, and local communities to keep bogs undisturbed for long enough to allow specialist species to return. UK reintroduction projects outside Cornwall show that butterflies may not appear until years after restoration begins, and even then, success depends on ongoing protection.
In the presence of the Large Heath, you can read the health of the whole wetland: deep peat holding water, cotton grass waving in the wind, mosses spreading like green quilts, and a community of specialist insects and plants living on the thin edge between land and water.
Restoring and protecting these places is about more than saving a single butterfly. It is about holding onto a rare, beautiful balance—one that, if we are lucky, might one day bring a bobbing flash of brown-grey back to Cornwall’s summer bogs.
