Invasive Species

The Spanish Slug (Arion vulgaris)

In the early spring of 2012, Arion vulgaris, commonly known as the Spanish Slug, was identified in the UK by Dr Ian Bedford, Head of Entomology at the John Innes Centre, Norwich. He noticed an unusually high number of slugs in his garden in spring 2012 and noticed they were not just eating plants but other things too such as dog excrement and dead animals. It was first thought to be a species of slug called Arion Flagellus, commonly known as the Spanish Stealth slug which was first identified in the UK in 1945-1946. After some further research and collaboration with Dr Les Noble, University of Aberdeen, it was discovered it was an ‘invasion’ of the Spanish Slug and it is thought that the slugs entered the UK on imported salad leaves, bare root trees or potted plants.

The Spanish Slug varies in colour from bright orange to light brown and can grow to a size between 8cm and 15cm when they have reached maturity.

The Spanish Slugs are known to:

  • Produce twice as many eggs as slugs native to the UK
  • Tolerate hotter and dryer environments
  • Have an extensive omnivorous diet which includes excrement, dead animals and crops that aren’t normally susceptible to slug feeding
  • Push out other slug and snail species to dominate an area, due to large size and high population density


During the growing season of 2012, slugs were the most widely reported pests, and throughout East Anglia catches of 3000-4000 slugs per month were not uncommon in home gardens. The reason these slugs thrived is because of the very wet summer we had in 2012 allowing them to grow quickly. But Spanish Slugs are able to tolerate dryer and hotter conditions having adapted to living in the Mediterranean. Their population has also grown rapidly because they don’t seem to have many predators as the huge amounts of mucus they produce repels any potential threat. Additionally the Spanish slugs can self-fertilise and lay around 300 and 500 eggs each, whereas native slugs only lay around 150 eggs each.


See more about the 2012 Spanish Slug outbreak from around the web at Scoop It!


Over recent years the Spanish Slug has been known to spread into parts of Northern Europe and caused severe crop failure in Scandinavia, there were even instances where slugs had been eating road kill and making the roads slippery.