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Supersized snails hold up border revamp at RHS Wisley

High-profile redevelopment by legendary designer Piet Oudolf put on hold for snail relocation project after discovery of protected species

The Glasshouse Border renovation project at RHS Garden Wisley brings together one of the world’s most renowned garden designers, years of planning, nearly two acres of border area, and an estimated 36,000 plants. However, one challenge the team could not have foreseen was for the project to be brought to a halt by a colony of supersized snails.

RHS Wisley’s iconic Glasshouse Borders are set to be transformed into an immersive perennial paradise by internationally acclaimed landscape designer Piet Oudolf, who created the original borders over 20 years ago. Renamed the Oudolf Landscape, this will be one of the largest and most significant examples of the designer’s work ever created in the UK. 

Work was due to start on the borders in the autumn of 2022. However, this all changed with the discovery of a colony of Roman snails, the UK’s largest land snail and a protected species that requires a licence to possess or handle. 


VIP snails

Roman snails are a

naturalised species in the UK, thought to have been introduced by the Romans for food. This is the snail that is still prepared in France as ‘escargot’. However, some of the UK’s populations were decimated by people collecting them for cuisine or selling to such an extent that in 2008, the snails were given nearly total protection under the Wildlife & Countryside Act in order to save the remaining colonies.

What sets Roman snails apart from other species?

These are the biggest land snails in northwest Europe by quite a margin, reaching around 4.5 centimetres – roughly the size of a hen’s egg. The nearest other land snail is the garden snail, which is about half the size. They also have a comparatively long lifespan – lots of snails live for barely a year, while Roman snails can live for between 10 and 20 years. So a Roman snail can out-live a dog!
 
– Dr Martin Willing, The Conchological Society of Great Britain and Ireland

Roman snails are very rarely found in gardens, and their UK distribution is restricted to pockets of southern England, making this an exciting find for biodiversity at Wisley. Their presence is all the more surprising given that Roman snails generally only live in alkaline limestone and chalk areas, while Wisley’s underlying rock is acidic sandstone. It is thought that the top-dressing of limestone chippings on the Glasshouse Borders made the area more enticing to the snails.

Shells of the Roman snail (Helix pomatia), garden snail (Cornu aspersum) and banded snail (Cepaea species)
A Roman snail. Image: Martin Willing
Roman snails benefit from similar legal protection to the great crested newt in the UK, making it illegal to handle them – dead or alive – or otherwise disturb them without a licence from Natural England. Any unauthorised tampering with a snail could land you with a £5000 fine or a 6-month prison sentence!

In order for the border renovations to go ahead whilst ensuring appropriate conservation of these majestic molluscs, a plan was drawn up to relocate the snails to another suitable site close by, which was prepared accordingly with limestone chippings to ensure the new residents felt at home. 

Dr Martin Willing, a molluscan specialist and Vice President of The Conchological Society of Great Britain and Ireland, was enlisted to train a team of Wisley horticulturists in identification, handling and recording of the snails. After training, this small but dedicated ‘snail team’ was now permitted to begin the relocation project.

How surprising is it that a population of Roman snails has been found at Wisley?

Frankly, they shouldn’t be there. The bedrock at Wisley is sandstone; Roman snails live on limestone and chalk. The nearest site to Wisley is probably eight or nine miles away on the North Downs. That may sound close, but Roman snails don’t travel – they spend their entire lives within a 30-metre radius of where they are born. So Wisley is way off their known range. The particular border in which they were found has a top dressing of limestone chippings, which the snails like. So, what should be an unsuitable place has, in a limited way, been made suitable.

– Dr Martin Willing


Snail sweeps

Starting in May, the snail team have been carrying out two ‘snail sweeps’ per week; carefully searching through the borders for signs of the snails. Though only a handful of individuals were expected, the team have so far found and relocated over 40 of the supersized molluscs.

Each snail must be individually recorded, photographed, and numbered with Tippex on the underside of the shell in order to keep track of individuals and ascertain whether they are returning to the original site. So far, the snails have settled in well into their new home nearby, and none have been found straying back to the Glasshouse Borders.

Recording and numbering has enabled the relocation project to develop into foundations for longer-term study of Roman snail ecology. Ongoing monitoring of the Wisley population over the next five years will provide insights into the relocated individuals’ movements and lifespans, adding to the body of scientific understanding of Roman snails in the UK.

It’s actually opening up a really interesting branch of research that will add to our knowledge of how these fascinating molluscs operate, and will help us conserve them elsewhere

– Dr Martin Willing
It is thought that relocation will be complete by the end of the summer. With all snails safely rehomed, renovation of the borders is set to start in autumn/winter 2023, with the new Oudolf Landscape planned to open in summer 2024.

Do the snails eat the border plants?
 
Yes they do! But they’re quite a small population and there are plenty of plants on the borders for them to eat. In general we don’t get too much damage from slugs and snails on the borders. I personally think this is because the sandy soil is dry in the summer and we clear the borders of vegetation when we cut back in late February, so there aren’t many good overwintering spots.
 
– Ian Trought, Horticulturist (Glasshouse Borders)

About the author – Olivia Drake

With a background in biology, Olivia is passionate about sustainable horticulture and the role gardening can play in conservation. She is trained as a botanical horticulturist and previously worked in public gardens around the UK and abroad.

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