How do you reintroduce an extinct butterfly?

Thursday 11 June 2020

Jenny Bennion

Jenny is our Peatlands Communications Officer, working hard to let people know all about just how precious our peatlands really are. Jenny is never happier than when scrambling around in bogs and mosslands.

The large heath butterfly is one of the species we're reintroducing in the Great Manchester Wetlands. Photo: Steve Rawlins - Chester Zoo

Locally known as the Manchester argus, habitat destruction forced the large heath butterfly into extinction across Greater Manchester well over 100 years ago, but through our Species Reintroduction project we’ve brought it back!

The large heath butterfly is one of those specialist creatures that is able to call our peatlands home. It has evolved to survive in these acidic boggy landscapes, relying on the hare’s-tail cotton grass and cross-leaved heath that grows there for the food source of it’s caterpillars and adult butterflies respectively.

It was once a common sight fluttering around our region’s peatlands, being so numerous in the Chat Moss area of Greater Manchester that it was locally christened the Manchester argus.

Peat extraction on Astley Moss in the 1960's - photo courtesy of Dave Woodward

What happened to the large heath butterfly?

The Industrial Revolution and the arrival of the railway to the area in the 1840s spelled disaster for our precious peatlands and the specialised wildlife that called them home. Throughout the 19^th century, and beyond, huge swathes of these peatland habitats were drained and the land converted to agriculture or the peat extracted for fuel.

With its foodplants and habitat completely eradicated, the large heath butterfly became completely extinct in the area.

But all was not lost. The Great Manchester Wetlands partnership Species Reintroduction programme hatched a plan to restore some of our region’s remaining peatlands and reintroduce the large heath butterfly.

First came the long, hard task of restoring our peatlands to an extent where they could support a population of large heath butterflies again.

The entrance to Lancashire Wildlife Trust's Astley Moss nature reserve — Rare birds like cuckoos and willow tits have been spotted on Astley Moss, which is a Site of Special Scientific Interst (SSSI)

Your Wildlife Trust has owned and managed Astley Moss SSSI since the 1980’s, working to rewet and restore the site to it’s former boggy glory, and so this seemed like a great place to concentrate our efforts.

Funded by Veolia and the Casey Group, the Species Reintroduction project, including experts from your Wildlife Trust and Natural England, set to work to further restore this habitat, on the border of Salford and Wigan.

Cross-leaved heath in flower with delicate pink flower heads — Cross-leaved heath by Ross Hoddinott/2020VISION

Restoration and reintroduction

Many classic peatland species had already begun to recolonise Astley Moss, including the peat-forming sphagnum mosses. This was then supplemented with further plug plants including the all-important hare’s-tail cotton grass and cross-leaved heath which the butterflies depend on for survival.

Now came the question of the butterflies.

Thankfully a population of large heath butterflies had survived at Winmarleigh Moss near Garstang, and after these had been used as donors for a successful reintroduction at Heysham Moss in 2016, permission was granted by Natural England to repeat this process, but this time on Astley Moss.

So June 2019 saw just six pregnant large heath butterflies collected from Winmarleigh Moss, and then transported off to Chester Zoo where a special breeding enclosure awaited them.

As with all things wildlife, the butterflies didn’t exactly stick to plan and proceeded to lay their eggs on the mesh of their enclosure, rather than in the hare’s-tail cotton grass that had been provided for them. However, the expert Chester Zoo keepers soon got the eggs in the right place with the aid of a very fine paintbrush and a lot of patience.

A tiny green newborn large heath caterpillar sits on a paintbrush — Large heath caterpillar by Chester Zoo

August 2019 saw the eggs hatch into extremely tiny caterpillars which got busy eating and growing, before burrowing down into the tussocks of cotton grass for the winter.

Then in March this year the caterpillars reappeared and started eating again, before metamorphosing into pupae to start their magical transformation into adult butterflies. The pupae were then attached to canes and transported to Astley Moss where a special release enclosure awaited them.

After checking the release enclosure twice a day for around a week, the moment we'd all been waiting for finally happened... the first Manchester argus butterfly emerged from its pupae and was released into its homeland for the first time in over 100 years!

Large heath butterfly at Astley Moss — One of the first large heath butterflies to fly on Astley Moss in over 100 years! By Andy Hankinson

Homecoming

The following three weeks saw more butterflies emerge in ones and twos until a population of around 50 large heath butterflies were now able to call Astley Moss home. And we’re delighted to say that they have already started breeding, so this time next year we may be looking at the first truly native population.

Further collections from Winmarleigh Moss are planned in the coming years to reintroduce the large heath butterfly to other sites from which it has been lost, including Risley Moss in Warrington.

This fantastic project is a collaboration between your Wildlife Trust for Lancashire, Manchester and North Merseyside, Natural England, Chester Zoo, Manchester Metropolitan University, Salford City Council, Wigan Borough Council, Butterfly Conservation, North West Rare Plant Initiative, Warrington Borough Council and Liverpool John Moores University.

This project is only possible due to the years of hard work put in by all of our partners to restore these precious peatlands to health, and turn them back into a suitable habitat for the return of this once lost species.