The RHS Cellar Slug Survey

Slugs – most gardens have them, but somehow these slippery creatures are often under recorded, with little known about which species are where in Britain. In fact, it was not until 2011 that we realised just how many species are established in Britain, when a detailed study of the fauna revealed 22% more species were present in Britain than we thought! Slugs appear to be the ultimate hitchhikers, able to move into and around the UK, popping up in unexpected places. Of the over 40 species of slug present in Britain, almost 40% of these are not considered native. As all slugs are hermaphroditic, they don’t always need to find a mate to reproduce, and in theory any slug of your species is a potential mate. Sometimes a member of a closely related species is all you need.

The cellar slugs (Limacus species) are great examples of this flexibility. The yellow cellar slug (Limacus flavus) has been present in Britain since at least the 1600s, and has always been strongly associated with human habitation. However, in the 1970s, some experienced naturalists suddenly noticed that these slugs had started to look quite different, soon realising that another similar looking species had arrived in Britain. Since then, it appears that the green cellar slug (Limacus maculatus) is increasing, spreading and appears to be replacing its yellow relation.

As part of my PhD, I’m asking the public to help me find out how the yellow cellar slug is doing now. By getting anyone with a garden out looking for these species, we can start to discover just how far this introduced species has spread, and whether the yellow cellar slug is as close to extinction as feared or not. You can get involved by looking at the identification guide and reporting any sighting of these species here: www.rhs.org.uk/slugsurvey 

Our records are collected via a special form on iRecord, so while they are informing my PhD research, they also feed in to the national recording scheme of the Conchological Society of Britain and Ireland. The main objective of this national recording scheme is to provide a detailed picture of the changing distribution of the fauna, and provide data on the conservation status of molluscs and their habitats.

The cellar slugs are also an excellent species to engage gardeners with, as an example of how slugs can be beneficial to the garden. Usually, slugs are assumed to be the villain, attacking prized plants and destroying delicious crops. However, the reality is only a handful of the species found in Britain are considered major plant pests. Most slugs also carry out important roles as decomposers, due to their truly omnivorous, or in the cellar slug’s case, specialised diets. Both these cellar slug species prefer to graze on decaying plant material, fungi, and moulds, with it almost unheard of for them to attack live plants.

Although slugs are often overlooked, under recorded and widely detested, they are an important part of the British fauna. If you feel inspired to look at this group more closely beyond the cellar slugs, look out for the FSC Biolinks slug identification courses and get yourself a copy of the excellent FSC AIDGAP key to the slugs of Britain and Ireland.

Image Credits: Cellar Slug Guide: Amgueddffa Cymru - National Museums Wales / RHS, Other images: RHS