Slugs are not only one of the most common garden pests they also top the poll for the most enquiries to the Royal Horticultural Society. However unlike most other leaf-munching visitors to your garden, they aren’t insects. Slugs are land-dwelling molluscs that are more closely related to clams than beetles or caterpillars. Most species of slugs are decomposers who feed on decaying plant and animal wastes but there is a handful of species that prefer to feed on living plant material and these are the ones we are after.
There are about 30 thirty species of slug in the UK but four of them cause the most damage costing up to £8 million a year and the average UK garden is, unbelievably, home to over 20,000 slugs.
Slug bait containing metaldehyde was very effective but has been banned from the end of March 2022 and has already been withdrawn from sale. It is proven to kill wildlife that feeds on the dead slugs, particularly hedgehogs, so we do not recommend its use. If you have any left in your shed please dispose of it responsibly.
But all is not lost, far from it. Millions of words have been written about the subject but here are a few ideas that might be of help. I suggest you don’t read this while eating your lunch!
1. Hedgehogs and frogs love to eat slugs, especially in the evening when they and the slugs come out to feed. Encourage frogs with small ponds and hedgehogs with nice dry areas for nesting and holes in your fence so they can get in and out of your garden. Racoons also love slugs but there aren’t many of them in Radlett.
2. Nematodes – these are colourless microscopic roundworms that carry bacteria that kill the host which the nematode then consumes. You need to buy one specific for slugs. They have a limited shelf life and are not cheap so follow the instruction closely. They are not harmful to wildlife.
3. Ferric phosphate slug pellets – these are still legal and are often advertised as organic. Slugs tend to disappear underground after ingesting them so are less of threat to hedgehogs. Their effect on other wildlife such as worms is still the subject of debate. It is recommended that these be used sparingly, maybe 4 or 5 in an area of an A4 size of paper.
4. Go out after dark and collect your slugs. Dispose of them as you see fit but salty water works well. The RHS suggests putting them in your freezer – rather them than me! I find scissors quite useful and hedgehogs can then tidy up.
5. Lay pieces of wood or other material flat near the plants. Hopefully the slugs will retreat under these in daytime and you can then lift them and dispose of as above.
6. Create barriers with various advertised remedies such as wool, grit, eggshells, copper and plastic collars. I have heard a lot about the failure of these methods but undeterred I have bought a stock of slug collars to try next season (see photo). The theory is that the slugs cannot climb over the rim – we shall see. I will even try sowing some seeds in the bottom.
7. Electricity – some enterprising gardeners have suggested a wire or strip with a small electric charge is an effective barrier particularly round the top of raised beds. Don’t be tempted to wire this up to the mains as you will not only fry the slugs and the hedgehogs but probably yourself as well. A 9 volt battery is sufficient and will, allegedly, last all season.
8. Beer traps set into the ground can work. The slugs are attracted by the yeast in the beer and fall in. The upside is that you can drink the beer that doesn’t go into the traps.
And I am sure there are thousands of other remedies out there so please let us know what works for you. I will report back on the slug collars next year.
And for those of you who are fascinated (perhaps the wrong word) by slugs here are a few more facts. As a slug moves it secretes a mucus which helps it glide across the surface and it moves at a top speed of about two feet per minute. The mucus trail also helps it navigate back home. They can go up or down at any angle, including upside down and can pass over a razor blade edge without harm. (doesn’t bode well for my slug collars). In freezing temperatures it alters its blood structure to prevent the forming of ice in the tissues.
Each slug is capable of laying hundreds of eggs over the course of its lifetime though the eggs are laid in clutches of about 30. They are laid in moist soil, under mulch or rocks, or beneath leaf detritus. They’ll sit dormant if the weather is too hot, too dry, or too cold, waiting for just the right moment to hatch. Leopard slugs, which don’t eat fresh plant material, are famous for their bizarre mating habits. They hang upside down and their reproductive organs, which come out of their heads are blue in colour. And those particularly large slugs you often find in your veg patch or allotment are probably Dusky Slugs (Arion subfuscus) or Large Red or Black Slugs (Arion ater), neither of which are the worst offenders.