I had assumed that the critters responsible for consuming many, and in some cases all, of the leaves on my chard, kale and basil plants were the larval stages of some type of moth or caterpillar. I did find quite a few on the kale plants, most likely cabbage moth larvae, but none on the chard and basil.Well after dark, while putting some gear away with a headlamp, I swung by the garden to check on the progress of some recent seedling transplants—and there, clinging to the kale, basil, chard and tomato leaves, I spotted the thief hard at work under the cover of darkness: slugs, and lots of them.
Slugs are essentially shell-less snails. The two groups comprise the gastropod class found in the Mollusca phylum. Among the classes in the animal kingdom, gastropods are second only to insects in total number of species.
Lacking a shell for protection from predators and the drying effects of the sun, our local slugs are nocturnal, emerging at dusk from their damp underground haunts and returning to them at dawn. Mucus covering the body provides some protection from desiccation and, because it makes the slug hard to pick up and hold, and is distasteful, it provides some protection from potential predators.
They are able to lose as much as 80 percent of their body weight in water without harm, in contrast to our ability to lose 12 percent without suffering ill effects. Apparently, my thorough job of mulching the garden beds provided excellent daytime cover for slugs and greatly improved their habitat.
There are four tentacles, or feelers, on a slug’s head. The longest and most noticeable is tipped with eyespots, while the lower, harder-to-see and shorter pair are olfactory sensors. A conspicuous hole in the right side of the slug allows air exchange to the lungs and is called the pneumostome.
The entire flat bottom of the slug is the muscular foot. Rhythmic contractions of this muscle create waves that propel the slug forward. Simultaneously, a thin layer of milky mucus that protects the foot is secreted, leaving a telltale slime trail in its wake. The slime trail is useful in finding mates and returning home from a night out ravaging the garden.
I seem to have at least two species of what are generally referred to as “garden slugs.” One is grayish-tan-colored and less than 2 inches long at rest (measuring the length of these stretchy critters that can double in length when moving is relative). The other, Limax maximus, whose common names include the leopard slug and spotted garden slug, has distinct black spots over a yellow-tan color and can reach 6 inches in length. (It’s possible that the smaller, unspotted slugs are juveniles and I have only one species inhabiting my garden.) I found a leopard slug halfway up my screen door one evening—along with a trail of inch-wide milky slime impregnated into the screen.
So, what to do about the “slugfest” in my veggie garden?
Picking the slimy individuals off plants at night is one strategy, but it’s a tedious and unpleasant chore. The slime is amazingly difficult to remove from your hands even with soap and hot water.
Slugs are attracted to beer (actually, the yeast in the beer) set in shallow containers among the plants, and once in they apparently drink themselves to death. Beer traps work—but who wants to waste beer?
One of the most interesting schemes for reducing slug populations is getting a duck. Ducks love slugs and are very effective at locating them in their daytime hiding places. And, as opposed to chickens, I’ve read that they don’t damage your plants.
Some species of slugs are omnivores, but most are listed as detritivores, consuming dead plants and fungi and helping to recycle nutrients in the ecosystem. As such, they provide an important ecological function.
Most of my references point out that many of the slugs found in our area, including the leopard slug, were introduced from Europe and Asia in the 1800s.