The voracious Spanish slug, Arion vulgaris, has become a problem in northern mainland Europe in recent years, decimating crops as far north as Scandinavia. With few predators, the slugs multiply quickly, pushing out other slugs and snails to dominate an area.
It was identified by Dr Ian Bedford, head entomologist at the John Innes Centre, who spotted the creatures in his East Anglia garden. Dr Les Noble from the University of Aberdeen confirmed the finding.
Bedford said: "It wasn't just plants that were being attacked by this species - they were eating dead animals, other slugs and snails, even their shells."
He added that coast of East Anglia "seems to be like an open door to all sorts of invasive species - I don't know if it's because we've got a number of ports here".
Bedford and colleagues at the University of Aberdeen and Newcastle University are developing a programme of research to find out more about the Spanish slug, its distribution across the UK and its impact.
If Bedford's suspicions are correct, there could be an explosion of the slugs in spring when their buried eggs hatch. "I've seen them in a potato field in the middle of summer, sliming across dry, sandy soil. The agronomist with me couldn't believe what he was seeing because slugs don't usually do that. It's a hardy species."