Slugging it Out in the Garden

Slug & snail damage on a Host

Slugs are a problem. They eat plants, and gardeners are famously annoyed by anything that eats their plants. Hence slugs are a problem.

Little Blue Pellets

In the olden days of gardening we dealt swiftly, and often preemptively, with slugs and snails. We did so by application of little blue pellets, always called “slug pellets”, never “slug death pellets” or “mollusc torpedoes”. These were always blue, because, as we all know, nobody eats blue stuff. They contained the active ingredient metaldehyde.

The big advantage of metaldehyde was its extreme effectiveness at killing slugs and snails. The problem with metaldehyde was its observed or suspected effectiveness at poisoning various other creatures, including hedgehogs, wild birds and domestic pets. These concerns eventually led to the emergence of alternative slug pellets based on ferric phosphate, which were pitched as being good at killing slugs and snails, and only them (although opinions may vary). These alternative little blue pellets are now the only version available to UK home gardeners and are considered acceptable in organic gardening.

Not Pellets

Alternative alternatives also exist. Many of these were invented before the advent of the ferric phosphate pellets, during the era when organic gardening was just starting to become more mainstream. Amongst these organic approaches were the famous ‘grapefruit skin trap’, and the ‘impenetrable ring of crushed eggshells’. Quite why anti-mollusc endeavours revolved around breakfast items was something of a mystery. Similarly mysterious was the action one was supposed to take with a grapefruits’ worth of slugs; slightly coy phrases along the lines of “dispose of as appropriate’ were normally the final instruction here.

While the grapefruit trick definitely does work (assuming you want to collect slugs), the record of the eggshell barrier is is little more patchy. Some people probably swear by it to this day, but by-and-large it has left the collective gardening consciousness, replaced by a range of alternatives. Coffee grounds, sheeps wool, petroleum jelly, sandy grit, gritty sand and copper tape are some of the slug proof barriers that have been suggested over the years. Some of them may even work some of the time.

But slugs and snails are persistent little devils, and eventually they will find a way around any barrier put in their way (assuming it evens works in the first place). So it’s unsurprising that slug execution has never been completely taken off the table. Those disinclined to use slug pellets do have a couple of options. Not only that, they are options that actually work.

Beer traps are another long-standing organic gardening method. They are surprisingly effective at collecting and dispatching slugs, you do need to use the right type of beer, slugs don’t like larger. A well positioned jam jar of cheap bitter will do a lot to draw slugs away from precious plants. You can even buy purpose made slug traps, which come with handy rain hats to stop the beer being diluted.

A slightly more recent innovation, the other successful slug control is biological. Specifically, a tiny nematode called Phasmarhabditis. As with many biological controls, these can now be ordered online, a packet comes through the post, you mix the contents with water, and apply to the soil or compost via a watering can. It’s no more complicated than mixing and applying fertiliser.

Both of these methods avoid the issue with pellets whereby recently poisoned slugs wander off and become a meal for some other wildlife, poisoning them also. The nematodes are only injurious to slugs (they don’t even bother snails), beer traps collect and contain slugs. With these “green” controls there is much less potential for collateral damage.

A Slug By Any Other Name

Anti-slug sentiment is definitely the norm in UK horticulture, but it must be admitted that there is more to slugs than is seen from the point of view of us gardeners. It could be argued that the other problem with slugs lies in our attitude to them. Today we are rightly concerned with preserving biodiversity, and land-based molluscs are unquestionably a part of that biodiversity. Indeed, species of slugs and snails are just as likely to become rare and endangered as any other living thing (a tiny and rare snail disrupted the building of the Newbury bypass some years ago).

There exists a diverse range of slugs in the UK, large and small, in a slimy rainbow of colours. Not all slugs will do damage in your garden, not all of them even eat plants, there are some carnivorous slugs that specialise in eating other slugs!

From an evolutionary perspective a slug is a snail that lost its shell. Clues to this transformation exist in some species that still possess useless vestigial shells, either internally or externally, like a kind of calcified appendix. Going without the shell means that slugs are much more susceptible to drying out than snails, and so must always find a damp hiding spot. This may seem like a limitation, but it also frees them from the need to find the large amounts of calcium used to build a shell, which in turn means they can colonise habits the might not be available to snails. Also, a streamlined slug is more able to squeeze into tight spots to find shelter or food.

But however interesting slugs may be in their own right, it cannot be denied that some of our favourite garden plants are irresistible mollusc meals (Hosta and Dahlia spring immediately to mind), and this can make it almost impossible to grow certain plants. This, of course, is why we try such a wide range of slug traps, barriers and treatments.

Over the decades the way we deal with slugs has changed, but our overall attitude towards them has not. The anguish of finding a favourite plant reduced to lace-doily status over night has driven many of us to extremes, to the point where they relatively passive methods outline above just don’t seem adequate. Some are moved to take direct action. Allegedly there are those who perform night-time patrols of their patch wearing head torches, collecting slugs (again, what do they do with them?!). Then there are others who skip the collection part and move straight from slug discovery to dispatching them with a pairs of scissors; I worry a little bit about these people.

But, as mentioned earlier, a slug is not just a slug, and it is from this point of view that the Royal Horticultural Society have recently decided to stop labelling slugs and snails (and other beasties) as ‘pests’. They think that this type of blanket labelling is unhelpful in a world where biodiversity is threatened at every turn. They do have a point, but I personally think they’ll have an uphill battle on this one. The chances of removing the word ‘pest’ from gardening language are slim to none, and not because we’re all hell-bent on killing everything that moves in our gardens (although, some of us still are). The issue is one of definition. Not every slug is a pest, but there are definitely slugs that engage in pest-like behaviour, that has not changed.

Whatever the future holds, I think it may be some time before we gardeners learn to love the slug. Maybe we should aim for disdainful ambivalence?