Network Rail celebrates World Habitat Day with biodiversity bonanza for rare butterfly: Green Down nature reserve with GWR train on the Castle Cary line

Monday 2 Oct 2023

Network Rail celebrates World Habitat Day with biodiversity bonanza for rare butterfly

Region & Route:
Wales & Western: Western
| Wales & Western

This World Habitat Day (Monday 2 October), Network Rail is celebrating a partnership with Natural England and Somerset Wildlife Trust that’s working to restore and enhance the habitat for a rare butterfly, the Large Blue, at Welham Cutting in Somerset. 

Large Blue butterflies were declared extinct in the UK in 1979 but were successfully reintroduced at a handful of sites across the south of England during the late 1980s and early 1990s. They particularly thrive in grassland habitats like Green Down, which is adjacent to Welham Cutting and part of East Polden Grasslands Site of Special Scientific Interest.  

Successful habitat management for the Large Blue involves providing suitable conditions for their unique lifecycle. The caterpillars feed on wild thyme and marjoram, which are vital for supporting the species. These caterpillars are then carried away by a specific species of red ant that mistake them for grubs and take them to their nest. The caterpillars feed on the ant grubs in the nest until they are big enough and turn into a chrysalis.  

One of the main priorities for supporting the Large Blue population is ensuring that these ant nests are at a suitable temperature. Network Rail has removed 40 ash trees on the rail embankment at Welham Cutting, as they were casting heavy shade across the grassland and reducing the temperature inside the ant burrows, negatively impacting the lifecycle of the Large Blue. The limited sunlight also affected the butterfly’s habitat quality, by reducing the number of flowering plants and insects. Many of the trees had ash dieback disease, so their removal also improved safety on the railway line and enabled easier maintenance of the infrastructure. 

Angharad Owen, Network Rail environment manager, said: “We have worked with a number of different stakeholders including Somerset Wildlife Trust, Natural England, and Large Blue Partnership to ensure that the habitat at East Polden will remain viable for these rare butterflies for years to come and I’d like to thank them for their efforts. 

“Any work that takes place at the site has to factor in a number of other environmental considerations, owing to the potential presence of protected species such as dormice and great crested newts, as well as the Large Blue. The location of the site also posed a number of challenges, with steep embankment sides. Together with our partners we have overcome these ecological and logistical challenges in a way that will benefit wildlife in the area into the future.” 

Mark Green, of Somerset Wildlife Trust, said: “We’re pleased that Network Rail has felled a section of ash trees along the railway adjacent to our Green Down nature reserve, which is home to a wonderful variety of plants, insects and birds, including the globally threatened Large Blue butterfly.  

“The tall trees were casting a heavy shade on an area of herb-rich, chalky grassland, with the effect of reducing plant and invertebrate species diversity in the vicinity. The reduction of the shading will enable the grassland to recover to a more optimal condition.  

“The work has been the result of a collaboration between Network Rail, Somerset Wildlife Trust, Natural England, Habitat Designs (ecologists with expertise in Large Blue butterfly conservation), and Ground Control, who carried out the felling, and is an example of how a partnership approach and carefully considered vegetation management can enhance biodiversity along the rail network.” 

To find out more about what Network Rail is doing to support biodiversity on the railway, visit  

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