The intrepid slug and power of slime

The slug, in theory, is a friend.

It belongs to a class of animals, called detritovores, that feed on the detritus of the living world so that it does not pile up endlessly around us.

Vegetation that is decaying, or has at least begun its downward descent from the prime of life is a slug’s food of choice. If only fresh, robust plants abound, it will make do. But as an alert gardener will note after thinning a row of seedlings, the plucked ones left to wilt on the ground attract slugs first, not those left standing.

Unfortunately, most any soft-leaved plant is fair game if slugs are hungry. They can be a serious threat to crops, leaving jagged holes in leaf, stem or fruit and sometimes wiping out young plants altogether. So notorious are these rampages, that one common species is even named Arion hortensis, the “garden” slug.

From our lofty height slugs are small, creeping blobs that leave trails of silvery slime. Pick one up and its sticky coating stays with you, no matter how much you wash your hands. This goo is secreted by the slug’s foot, a muscular organ that rhythmically propels it forward. It creates its own slippery river on which to glide, its delicate body thus protected from the abrasive ground.

Look at a slug closely, the way a child would, and you’ll see a comical little face with two pairs of feelers; the upper, longer pair for seeing, the lower for smelling. “Kids love slugs”, says my sister Anne, who has worked with the very young. “They find them fascinating, put them in jars. A slug is the perfect pet. You can always get another one.”

In a typical year, slugs make an early appearance, because they thrive on the moisture that goes with spring. In a dry year you might not give them a thought — until a spell of rainy weather hits. Suddenly there are holes in everything. Lettuce and cabbage must be soaked in the sink, leaving trails and drowned bodies on the bottom.

There are several ways to cope. Hunting and trapping slugs, even when their numbers seem infinite, are effective if you keep at it. On wet days when they’re not hiding from the sun you can pick them up with tweezers or tongs and dispose of them in a jar of soapy water. Stalking them at night with a flashlight also is fruitful. The simplest approach is to put down boards, shingles, cardboard — anything they can hide under — then lift these each morning to harvest your prey. You can even use old, yellowed broccoli and cabbage leaves, or grapefruit rinds turned upside down like igloos. The classic lure is beer in a saucer (they love anything fermented) but a bottle of it turned on its side is harder to escape from.

Sprinkling the ground with rough, sharp materials that hurt their soft bodies is supposed to help. Cinders, ashes, diatomaceous earth or sand are unpleasant to slugs when dry, but less so when moist, and it’s in wet weather that you need them to work. Besides, a determined slug can deal with sharpness. Photographs in Ralph Buchsbaum’s 1938 textbook “Animals Without Backbones” show one crawling over the upright blade of a razor. Such is the protective power of slime. Copper strips, which give slugs a mild electric shock, are a better deterrent. They’re expensive, but worthwhile if nailed to planters and small raised beds, or used as a mini-fence around rows of new seedlings.

The best tactic is to make the garden slug-unfriendly by cleaning up plant debris (except when using it for entrapment). Keep your beds from becoming moist, dark, slug jungles by thinning crops, spacing them well, staking or trellising to keep them off the ground and picking off their lower leaves.

Mow grass and weeds around the garden’s perimeter; these harbor more slugs that might creep in. Avoid mulch if populations are high. Raise transplants in pots until they are big enough to hold their own against a few nibbles. Keep the pH neutral, since slugs like acid soil. Clean up the garden in fall, composting all the dead leaves and raking the soil to expose slug eggs to predators. Keep plants as well-fed and healthy as possible, then pull them out when they are no longer productive — unless you are saving seed from them, or letting them bloom for the bees.

Stressed, diseased, senescent or damaged plants give off the death vibes that slugs are drawn to.

Most important, resist the urge to use toxic baits. Keep the garden safe for your allies — the numerous species who find slugs a nutritious snack, slime and all. These include ground beetles, salamanders, snakes, toads, frogs, turtles, centipedes, firefly larvae, skunks, robins, woodpeckers, ducks, geese and a host of friendly grubs. Invite them in. Well, maybe not the skunks.

Barbara Damrosch

Barbara Damrosch

Barbara Damrosch’s latest book is “The Four Season Gardener’s Cookbook.”

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