Slugging it out in garden

Slugs are not popular animals, writes Dick Warner

No wildlife conservation organisation is going to adopt a slug as its logo — they just don’t compete with pandas or dolphins or robins. This is understandable. They don’t look very attractive and they’re slimy. The slime absorbs water, which makes it difficult to wash off your hands. They’re also capable of doing quite a bit of damage by eating garden plants.

I didn’t realise I had slugs in my greenhouse until my wife began complaining about the large numbers of them hiding in the early lettuces that I proudly brought into the kitchen for her to use in salads. However, slugs are everywhere. They’re far more widespread than snails because they’re not restricted to environments providing enough calcium for shell building.

A survey estimated that the average garden in Britain contained 20,000 slugs. I don’t think any similar research has been done here but our climate is a little bit wetter and dampness suits slugs, which have evolved from marine organisms.

However, you probably don’t realise that you have at least 20,000 slugs in your garden because, at any given time, about 95% of them are underground, hiding in the soil. The remaining 5% are largely nocturnal and only active in daylight hours on very wet, grey days. They are hermaphrodites which means every adult slug can breed, with or without the assistance of a mate.

They lay eggs in batches of 20 to 100 several times a year. They have a life expectancy of five or six years so it’s been calculated that an individual animal has the potential to have 90,000 grandchildren. There are a lot of them about. Slugs are gastropod molluscs and belong to the second largest class in the animal kingdom, exceeded only by insects.

And, of course, they play an important role in the ecology of your garden. Their abundance, plus the fact that they don’t hibernate as snails do, makes them an important, year round, source of food for many birds and small mammals. They’re nutritious and relatively easy to catch.

Most Irish slug species are herbivores, though there are a couple of carnivorous ones, and they have an average of 27,000 teeth which they can renew when they wear out. When they use these teeth on young seedlings they can do devastating damage in one night. However, most slugs prefer dead plant material to living tissue. This places them among the detritivores, those invaluable organisms that dedicate themselves to cleaning up the rubbish and recycling its nutrients.

Over millions of years, they have embedded themselves as vital links in the complex food chains that bind together modern ecology.