Large Heath Butterfly Populations Reflect Peatland Health Across UK and Ireland

The status of the Large Heath butterfly is closely linked to the condition of lowland raised bogs, which are important wetland habitats in the UK and Ireland. Monitoring this species provides insight into the effectiveness of peatland conservation and restoration efforts.

The Large Heath butterfly depends on wet bog environments and specific bog plants, making it a useful indicator for assessing habitat quality. Its presence is often associated with well-maintained peatland areas that support a range of specialist species.

Between 1976 and 2014, the UK range of the Large Heath butterfly decreased by nearly 60%, a decline attributed mainly to the loss of lowland raised bogs. The butterfly is currently listed as Endangered on the British IUCN Red List and is considered Vulnerable on the European and Irish Red Lists.

Conservation activities have produced some positive results in specific locations. In Cors Fochno, Wales, peatland restoration has maintained stable populations of the Large Heath butterfly. In Greater Manchester, reintroduction efforts led to over 90 recorded flights at Astley Moss in 2023, indicating successful establishment in the area.

What the numbers show

• UK Large Heath butterfly range declined by about 58% between 1976 and 2014
• Butterfly Conservation’s 2024 survey found Large Heath in 21 out of 32 surveyed Scottish bogs
• More than 90 Large Heath flights were recorded at Astley Moss in 2023

Butterfly Conservation’s spring 2024 survey examined 53 priority lowland raised bogs in Scotland, with the Large Heath butterfly found in 21 of the 32 bogs surveyed to date. These findings help track the species’ distribution and inform future management actions.

The Large Heath butterfly relies on Hare’s-tail Cottongrass as its larval host plant, which requires a high water table to thrive. Peatland drainage, harvesting, and re-wetting can alter habitat conditions, sometimes making areas unsuitable for this species.

Peatland habitats also support other indicator species, such as Marsh Saxifrage, Vertigo geyer snail, Sphagnum austinii moss, and Willow ptarmigan. The presence or absence of these species, alongside the Large Heath, helps measure the ecological health of bogs.

Climate change and human-driven activities, including afforestation, peat extraction, and drainage, continue to threaten the survival of the Large Heath butterfly. In Ireland, drainage and harvesting have impacted populations, and certain restoration approaches have not always created suitable conditions for the species.

* This article is based on publicly available information at the time of writing.