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Groundbreaking planting initiative launched to attract purple emperor butterfly

Nestled in the heart of the Forest, a remarkable conservation success story is unfurling its wings. As the recent State of Nature Report shows, the UK is grappling with the serious decline of butterfly populations.

08 Dec 2023

But here in the Forest emerges a beacon of hope and inspiration. The 2015 Butterfly Conservation report showed that butterflies decreased nationally by 16%, while in the Forest we saw a 14% increase over the same ten-year period.

And now, hundreds of goat willow trees are taking root in South Derbyshire as part of a groundbreaking initiative to attract one of the UK’s most iconic butterflies, the purple emperor, to our region for the first time.

This large and magnificent butterfly dubbed ‘His Imperial Majesty’ has been slowly moving through the UK, colonising woodland in adjoining counties. And to encourage it further, the National Forest is supporting East Midlands Butterfly Conservation and South Derbyshire District Council to spearhead a project to establish the species in Derbyshire and help its northward route.

The group has funded the purchase of 550 two-year old goat willow trees, which will help create the perfect habitat for the species to thrive and become established.

The first of these trees will be planted on Thursday 30th November at Rosliston Forestry Centre and leading on from this, other partners have pledged to support the project with tree planting. These include The National Trust at Calke Abbey, Staunton Harold and Foremark, Mimi’s Wood, Grangewood, Catton Park and other woodland sites in the area.

At the core of the Forest's success in increasing the butterfly population lies our unwavering commitment to habitat creation. The strategic planting of goat willow saplings serves a dual purpose – contributing to the overall biodiversity of the area while specifically addressing the habitat needs of the elusive purple emperor butterfly.

The goat willow, a deciduous tree native to the UK, plays a pivotal role in this conservation tale. Recognised as a favourite of the purple emperor butterfly, which is primarily a woodland species, the trees’ leaves provide an ideal substrate for the butterflies’ eggs, and its sap serves as a crucial food source for caterpillars. By introducing these saplings strategically, we are actively encouraging the resurgence of the purple emperor in the region.

There are dozens of varieties of willow, also called sallow, but it is known that the purple emperor (Apatura iris), prefers the broad-leaved goat willow (Salix caprea), although eggs and larvae have been discovered on other varieties, notably grey willow (Salix cincera). So, these are the two types that are being planted.

Further advice has been from Matthew Oates, a well-known naturalist and volunteer for Butterfly Conservation. He has studied and written about the purple emperor. Long term, detailed studies of individual species are a huge help in any conservation effort.

Matthew says that the male butterfly likes a sheltered high spot, often around mature oaks, where he can look out for and fight off other males, as well as see females approaching. Mating tends to occur around the middle of the day and then the female butterfly lays her eggs on willow in the afternoon on leaves which are in the shade.

So, the trees will be planted in groups of three or four as a mixture in woodland rides on the eastern side of a wood, so the leaves catch the sun in the morning and are shaded in the afternoon.

Eggs are laid late July/early August, and the early larval stages are eating until early November. During this period growth is quite slow, reaching only around 10mm before hibernation, when they could fall prey to predators, so they usually assume position by a bud, a twig junction, or a cleft in the willow branches where they remain camouflaged.

But as soon as the buds open in the spring, the larvae begin eating voraciously and quickly grow during April and May, often quadrupling in size. Pupae form over three weeks from late May to mid-June, with emergence of the adult butterflies taking a similar time – males usually before females.

Adults are on the wing from mid-June to early August and that is the key time to be looking out for them!

By addressing the specific requirements of the purple emperor butterfly, the National Forest exemplifies how targeted actions can make a significant difference in reversing the fortunes of a particular species. By planting suitable habitats and effective woodland management, the Forest is a living example of how people and nature can thrive together.

If you'd like to help us continue to support wildlife and create habitats in the National Forest, then find out you can support our work, here.

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