Later on Tuesday I attended a workshop run by SLEF to learn to identify species in this much maligned and under-recorded group. Up to this point the only records of slugs on Raasay come from some casual recording on two short visits to the island giving a total of 10 species (out of the national list of about 40 species). The full Raasay list is below. As preparation for the course, I dutifully hunted slugs in the most convenient place – the garden. It was surprisingly difficult to find them in spite of the recent rain but it proved very productive.
I managed to find seven species including an unusually marked specimen of Limax maximus, (often known as the Tiger or Leopard Slug). Of these species, four were new to the island and were of particular interest. All four new species are associated with gardens and human disturbance. The garden habitat is one not searched during the previous short visits to the island. It is quite likely that the recorded distributions of slugs (and many other species) omit many common species found mainly in garden habitats – naturalists will spend far more time in exciting, wild habitats looking for rarer, more exciting species. The first of the new species was not surprising – one of the pestilential garden slugs, Arion owenii. This is very common but grossly under-recorded. Until the 1970s it was not separated from two other garden slug species. Records before that time cannot be assigned to this species as both it and another common garden slug species, Arion distinctus, occur on the island. Since the 1970s, little slug recording has been done in this area so the species remained unrecorded, even from Skye, until recently.
The other three new species are all species that are spreading and the spread has been facilitated by human activity. Slugs or slug eggs are transported unwittingly in plant pots or other garden artefacts from one place to another and it is possible that climate amelioration has allowed some species to survive and thrive in increasingly northward locations. The three new species are Boettgerilla pallens, Deroceras invadens and Tandonia budapestensis.
Boettgerilla pallens, the Worm Slug, is a small, elongated pale grey slug, often with a lilac tinge. It is usually only seen in small numbers and not a pest, indeed its diet is thought to be very small invertebrates which themselves may be pests. It is a European species first recorded in the UK in 1972. Since then it has spread widely and is now present from Jersey in the far south to Orkney in the north. The first Skye records were only a decade ago.
Deroceras invadens (sometimes called the Tramp slug) has taken longer to spread having first arrived in Britain in the 1930s. It is now abundant in many gardens where it can be a pest. It is easily recognised with its brown body, and always has a pale area around the breathing pore.
Tandonia budapestensis, the Budapest Slug, is a major pest of potatoes and has been in Britain for about 130 years. Unlike many other introduced species, its spread has been very slow and it is relatively uncommonly recorded in the Highlands. However, it is likely that it is far more common than it appears as so little recording has been done in ‘human’ habitats.
Fuller descriptions and pictures of all these species can be found in the web site Mollusc Ireland: http://www.habitas.org.uk/molluscireland/index.html
Thanks to Chris du Feu and Roger Cottis for sorting out the above.