Experts fear that the Spanish slug, above, could breed with native varieties to form a hybrid combining the worst of the Spanish slug with tolerance to frosts and cold from British species. Photograph: Steffen Hauser/Alamy
The gardens and fields of Britain were saved from a grim invasion this spring. Thanks to the sharp, late frosts of May, millions of giant Spanish slugs – which threatened to devastate plants across the country – were killed. Never has so much been owed to such a poor spring.
But now experts fear that Arion vulgaris – which was first spotted in East Anglia a year ago – may soon make an unwelcome return to our shores. They have decided to seek public help to spot a menace which one expert described as “a disaster waiting to happen”.
A group of scientists led by Dr Ian Bedford, head of entomology at the John Innes Centre, Norwich, have created a “slugwatch” website – slugwatch.co.uk – so people can report where and when they have seen Spanish slugs. There will also be instructions on building traps to catch them. The project will be launched to coincide with UK Biology Week, which started this weekend.
“The Spanish slug is a voracious predator that can survive eating many of the slug pellets that are supposed to kill them. It eats crops spared by our native slugs, tolerates drier conditions, reproduces in greater numbers and even eats dead animals and excrement,” said Bedford. “We want photos and sightings from members of the public to help build a picture of how widespread the Spanish slug is. The reports may also give us an idea of whether it is breeding with native species to form a hybrid combining the worst of the Spanish slug with tolerance to frosts and cold from our own species.”
The Spanish slug was first spotted in Britain by Bedford in his Norfolk garden. “Every day there seemed to be more of them. One day I counted 350. I decided to send samples to check their identity and they turned out to be Spanish slugs.”
The species appeared in Scandinavia a few years ago, where they bred so quickly that squashed slugs on roads became a serious traffic hazard. Very soon, it looked as if Britain would follow suit. “In early spring, numbers of the slugs began to appear and it looked as if we were in trouble,” said Bedford. “But the late spring frosts seemed to have killed off baby Spanish slugs and saved us – for the time being.”
Scientists stress that slugs play an important role in the ecosystem: they are natural composters, breaking down vegetation, and provide food for our hedgehogs, toads and some garden birds. Of the 30 native species in the UK, only four are classed as pests: the netted or grey field slug, the garden slug, the keeled slug and the large black slug. However, the Spanish slug could prove to be an even greater threat.
“We need to know exactly how they are distributed and that is why we have set up this website,” said Bedford. “We need public help, badly.”