Where Did My Slugs Go?

Usually, I share what I know about gardening. Today, I’m going to do the opposite: I’m going to share my questioning. I’m faced with a horticultural mystery for which I can’t find an answer: what caused the near-disappearance of slugs in my yard?

First, a bit of history. There used to be thousands of slugs on my property: the proof is that, every morning on my morning walk in the garden, I would crush dozens of them, hundreds every year, and for nothing, because the next day there were just as many. But about 5 years ago, after years of fruitless crushing, suddenly the population dropped, to the point where I can now say there are essentially no slugs left in my house. Granted, we find 3 or 4 every year, but nothing to worry about.

A New Bug

Around the same time as the slugs disappeared, snails appeared (remember that slugs don’t have shells, but snails do). They were snails with bright yellow shells, sometimes, but rarely, with brown spirals. At first, I thought of them as being as bad as slugs, and I crushed them as I discovered them. But I soon realized that, unlike the slugs that left the foliage of my plants in shreds, snails don’t seem to eat my plants. So I did some research to find out more.

I came to the conclusion that the yellow snails invading my plantations were garden snails, either Cepaea nemoralis or C. hortensis (the two species are almost identical). And both, indeed, rarely eat green leaves: their staple food is dead, yellowed leaves. In other words, they’re decomposers! And they clean your yard for free! Needless to say, I immediately stopped crushing them.

It has to be said, though, that garden snails do sometimes attack green leaves, but only those of certain plants. I’ve heard they love nettle leaves, for example, but who’d complain if they ate weeds? At home, I’ve discovered just one ornamental plant that they happily eat: Allium ‘Mount Everest’. Curiously, they won’t touch any other allium, even varieties genetically close to ‘Mount Everest’.

A Link With the Disappearance of Slugs?

Is there a link between the disappearance of slugs and the appearance of snails? You’d think so, but over the years I’ve consulted several mollusk experts and none of them seemed to think that was the reason. According to them, the disappearance of slugs at the same time as the appearance of snails is just a coincidence.

So why have my slugs disappeared? Here are the theories I’ve heard or come up with:

Mulch Disturbs Them.

This theory holds that slugs don’t like mulch, as it’s difficult for them to get through this layer of irregular particles. What’s more, slug enemies such as ground beetles proliferate in mulch. And I mulch a lot at home. In fact, the area covered with mulch has increased enormously over time, from 0% when I bought the house to probably 75% today. Is this what has scared off the slugs? Maybe it did!

There’s Less to Eat Than There Used to Be.

Slugs love hostas, lettuce and a host of other garden plants. Now, as a laidback gardener, I started a campaign many years ago to eliminate “problem plants”. So I pulled out all the hostas that were being eaten by slugs and replaced them with hostas that slugs don’t like. As for lettuce, bye-bye curly lettuce, the slugs’ favorite. I now only grow romaine lettuce, which they disdain. And so on. By methodically eliminating the plants the slugs prefer, I may have driven them out of my field?

There’s Some Kind of Slug-Killing Disease on My Land.

The malacologists I consulted didn’t seem enthusiastic about the idea, but perhaps it would explain their rapid demise better than anything else.

Mind you, I don’t use anti-slug products, I don’t set beer traps or other slug traps, and I soon discovered that eggshells don’t keep slugs away, despite popular belief to the contrary. So, like all gardeners, I should have thousands of slugs.

And here I am, still asking myself the same question. Why is it that I’m almost slug-free at home? I’d like to know so that I can share this happy state of affairs with other gardeners. If there’s a malacologist out there listening, I’d love to know what they think!

A Sad Surprise

Last week, I made a terrible discovery. Two gigantic slugs, not the usual little grey slugs (Arion hortensis), but monsters 17 cm long and as wide as a cigar. A few days later, I found another one; my neighbor had killed 5 of them. I looked up the identity of this newcomer on the Internet: it would appear to be the leopard slug (Limax maximus), native to Europe but well established in parts of North America. Is this the start of a new plague?

Well, maybe not. It seems that this slug, as gigantic and disgusting as it is, is above all a consumer of microscopic fungi… and is also a predator of other slugs! It only eats plants secondarily. I’ve also heard that they don’t tolerate cold winters. Last winter was very mild, but a “normal” winter for this region may prove fatal.

I assume these new slugs arrived in my neighborhood on plants imported from elsewhere (the giant slug, it seems, is well established in Oregon nurseries, where the bulk of our trees, shrubs and evergreens come from).

So if you see a slug as wide as a cigar and almost as long, you’re not dreaming. But I suggest you do as I do and crush it: we don’t need another slug in the area, even if it is a mushroom lover!

---

Larry Hodgson published thousands of articles and 65 books over the course of his career, in both French and English. His son, Mathieu, has made it his mission to make his father’s writings accessible to the public. This text was originally published in Le Soleil on August 28, 2006.