Tony Dickerson problem solves
QHow do I identify Spanish slugs from native ones? Robert Holden, by email
ASpanish slugs are very large, measuring up to 18cm (7in) at maturity but there are a couple of native slugs that also grow large, too. It’s very difficult to distinguish these different species, especially as they can hybridise with each other. Some of the features that often indicate Spanish slug ( Arion vulgaris) is a dark grey sole and a dark rim around the breathing pore. They also tend to produce much larger deposits of slime. Although newspaper reports suggest the Spanish slug came to the UK in 2010, it has probably been here since at least the 1950s. Native to southern Europe, it’s now invasive in many northern and eastern European countries, having spread on imported fruit and vegetables. There has been a lot of interest in this species in the press in recent years, but much of it’s exaggerated. It can be a pest in a variety of agricultural crops and is usually found in human habitats, such as farms and gardens, rather than natural areas. A. vulgaris may have replaced native species such as the black slug ( A. ater) and the red slug ( A. rufus) in some areas in the UK, and probably also causes more damage.
The control options for Spanish slugs are the same as for other large arion species. Reducing their numbers is the first step, so – as the majority of feeding takes place after dark – examine plants by torchlight on a mild evening and remove slugs by hand.
To kill slugs, you can go down the biological control route with nematodes (which are safe for children, pets and wildlife), or put down slug pellets (effective, but generally unsafe for children, pets and wildlife). Scatter pellets thinly around vulnerable plants in accordance with the manufacturer’s application instructions. Pellets containing ferric phosphate are approved for use by organic growers.