The large heath butterfly had not been seen in Heysham Moss, Lancashire, for more than 100 years. In 2012, Chester Zoo partnered with the Lancashire Wildlife Trust (LWT) and Lancashire Environmental Fund (LEF) to develop a project to reintroduce the butterfly to the area.

Before reintroduction could commence, extensive restoration work was carried out by LWT to ensure Heysham Moss was suitable to support the species. Two key plant species are necessary for the butterfly’s survival: Hare’s tail cottongrass, Eriophorum vaginatum, food for the larval stage; and cross-leaved heath, Erica tetralix, an important nectar source for adults. To help both prosper, LWT carried out land management to ensure they were present in sufficient quantities.

Both plants were also propagated by the Horticulture Team at Chester Zoo to provide a food source for the captive breeding phase of the project.

In 2013, five female butterflies were collected from a donor site at Winnmarleigh Moss. The butterflies were carefully checked, mated and then moved to bespoke enclosures at the zoo for egg laying and larvae rearing. Under the meticulous care of the keeper team, the butterflies were raised in controlled conditions, a process which has been successfully repeated three times.

Over the last three summers, captive-bred pupae have been transported to Heysham Moss, and to date more than 300 butterflies have been released. Butterflies were observed in copulation immediately after the first release and adults were observed prior to subsequent releases, giving  a strong indication the population is becoming self-sustaining.

Large heath butterflies are now being monitored at both Heysham Moss and Winnmarleigh Moss, to keep a close eye on the two populations. Habitat monitoring will also continue to ensure it remains suitable for the species.

This project description was written by Cat Barton, Field Conservation Manager, Chester Zoo

Species profile
Large heath butterfly (Coenonympha tullia)

Habitat and Range
Restricted to open, wet boggy habitats in northern Britain and Ireland where hare’s-tail cottongrass, Eriophorum vaginatum, is present.

Conservation Status
A population decline of 43% since the 1970s with England and Wales being most severely affected. The butterfly has remained relatively widespread in Scotland and Ireland. Priority Species in the UK Biodiversity Action Plan. Fully protected under the Wildlife (Northern Ireland) Order 1985

Red Data Book of European Butterflies status: Vulnerable
GB Red List status: Vulnerable

Threats
Habitat Loss – predominantly due to drainage of boggy habitats for agricultural conversion

Vital statistics
Wingspan: 41mm
Maximum recorded movement: 650m
Always rests with its wings closed
Size of the underwing spots vary across its range
On the wing from late June to August