In the warmer months, my humid and lush suburban backyard becomes a battlefield for my war against slugs. I would have expected this seasonal plague of slugs in the country or a rainforest. Yet, slugs roam this area that is just about ten miles west of the skyscrapers of downtown Baltimore. And I want the small patch of land I own to be free of them.
It all started on October 3, 2014. The temperature was in the upper 50s, cool enough to require long pants and a flannel. Sitting in our backyard, my partner Dan and I were enjoying a small fire in our terra cotta chimenea and drinking cold beers. Thirsty for another sip, I reached for my can, which was by my feet. I gasped. Hanging out by my can of Miller Lite was a slug the length of my palm. I abandoned my seat as if it were on fire and fled indoors.
Our backyard light had illuminated this leopard slug, or Limax maximus as it is known in Latin. These slugs are light brown with dark brown spots, evoking an army of slithering leopards. And their bodies grow to be at least four inches long by early fall. Dan says he’s seen one in our backyard that was about seven inches; he has a picture, which I have yet to dare peek at. Ever since our first summer in Baltimore, when he sighted these low-lying mammoths, he has been intent on ridding them from our yard.
Slugs meander freely after sundown, a time when most people are tucked indoors, but not Dan. A smoker, he especially enjoys the tranquility the night offers as he inhales and ruminates on his writing, teaching, and research — that is, until a giant slug tries to drink his beer or climbs onto his pants or otherwise distracts him, such as by scaling the outdoor basement steps on which he sits or crawling into and out of the drainage grates.
Before I’d seen the Miller Lite slug, I thought he’d been exaggerating about their size or number. Now, their very presence shocks and disgusts me, and I feel guilt at the lack of support I had given Dan when he’d lined our outdoor basement steps and drains with pennies. He’d read that copper deterred slugs — gave them an electric shock — and we had lots of pennies in our coin jar. After each rainfall in the spring, summer, and early fall, he would sprinkle salt — sea salt, salt with iodine, rock salt, or salt pellets — around the areas where we liked to sit and enjoy the warm evenings. I’d lectured him for contributing to our watershed’s ruin, but I would reprimand him no more. I accepted the slug as our common enemy and prepared for their eviction from my land. First, I studied them; I needed to learn about my enemy. Then, I evaluated my options to force their exodus. Finally, I took action.
The Limax maximus, an invertebrate in the phylum Mollusca, and belonging to the subclass Pulmonata that also includes snails, has evolved over millions of years. Unlike its water-reliant cousins with gills, this land slug breathes with lungs. Though its ancestors once had hard shells covering their bodies, the modern offspring of the Limax maximus has shed this armor. Perhaps it did so to move at a quicker pace, and it does move faster than a snail, for example.
“Slugs are like a leaky bag of water that survives [on] dry land,” says Dr. Timothy Pearce, assistant curator and head of the mollusks section at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania. It’s no surprise, then, that the land slug prefers wet or humid landscapes with lots of hiding places (like under mulch, inside drain pipes, and under piles of fallen and decomposing leaves). And the Mid-Atlantic, as well as other stretches of land east and west of the Mississippi River, provides this oasis for the leopard slug. Its embrace of America is perhaps not surprising given that it has been here for over a century. As a result of global transport of organic commodities, the leopard slug first sailed to the North and South Americas about a hundred and fifty years ago. The leopard slug is aggressive and will bite slugs native to the Americas, such as the banana slug, to get what it wants — food or territory. The leopard slug will even eat a dead slug. To stay hydrated during the day, they lurk under stones, decaying tree trunks, or under the wide leaves of plants such as the hostas that line my front patio’s edge.
Because it is not indigenous to the Americas, Pearce calls the leopard slug an invasive species, “like the python to the Everglades.”
Slugs prefer to hang out with people.
Megan Paustian, a researcher with the National Museum of Natural History in Washington, DC, says leopard slugs have an affinity for urban areas, suburbs, and other disturbed places near people. It turns out that this is a common trait of invasive species. “People incidentally provide shelter (drainpipes, woodpiles, gardens, walls with cracks in them, etc.) and food (e.g., in trash cans, food left for pets), which is why they do so well around us,” she says. These slugs make do with what they can find and stick close to their familiar surroundings. Their apparent low-maintenance attitude seems to have helped them thrive as a species.
Leopard slugs eat a lot. Pearce describes them as being “a stomach on one large foot.” Paustian says leopard slugs “are omnivores and scavengers; they’ll eat dead plants and garden plants, fungus, and carrion.” They’re aggressive when it comes to acquiring their food and shelter, enough so to bite their competition to hold ground as King or Queen. But what they eat, they release to the environment. “Slugs and snails, in general, are important as decomposers, helping to return nutrients to the soil,” Pearce says. Their waste is rich in nitrogen, providing a beneficial nutrient to the land that nourishes and nurtures them. And when the slug’s life cycle ends due to the tongues of frogs or the beaks of ravens — some of their natural predators — it too becomes part of the dead, organic earth.
Though hermaphrodites, leopard slugs prefer to copulate with a mate, and they reproduce fiercely. Indeed, I have seen two slugs consummate this need. It was that same October, but a few days later on a Saturday afternoon. The sun’s rays shone the brightest on the copulating pair. The bluish slime their lust produced created a halo around the pair as it swayed, suspended like a double helix from a bent flower stalk that towered about two feet above its parent hosta plant. So entwined, the pair looked like miniature snakes preparing ritualistically to wreak havoc on their fellow beings.
Farmers and gardeners perceive the leopard slug as an omen. This slug destroys crops, eating seedlings whole. In my garden, they have been an obstacle to growing kale and mustard greens from seeds. The few plants that do sprout barely make it to the size of a three-by-five index card before a leopard slug bites into the leaves, making them look like slices of Swiss cheese. Pearce shares my frustration. He’s a gardener, too, and, though he loves mollusks, he is irritated that the leopard slug competes with him for his garden’s greens. But there’s no “silver bullet” for getting rid of them, he says. Whenever he finds slugs, he kills them by “cutting them in half.”
II. Explore Strategies to Deter Slugs from My Yard
- Salt keeps slugs away, but pouring it on soil harms other plants and the freshwater. Pouring salt directly on slugs’ bodies causes them pain. I don’t want to cause any sentient being that agony.
- The leopard slug that hung out by my beer that October day was probably drawn to the yeast in it, or the hops and barley. Gardeners sometimes use this yellow brew to attract and drown slugs. But beer, even in a can, costs money, and I prefer not to share my beer with a slug or use this otherwise therapeutic beverage as a murder weapon.
- Pesticides, while effective for some pests, may not work on the leopard slug: its slime can actually protect its skin and innards from chemicals. And these chemicals, as Rachel Carson cautions in Silent Spring, don’t just hurt the intended target; they hurt other living creatures such as the frog that enjoys the occasional slug for dinner.
- Copper, as Pearce substantiates, is perhaps the best deterrent because it gives slugs an electric charge upon contact. I’ve considered laying large strips of copper over my entire yard. The oxidation could be interesting to observe. At about $3 per pound, buying enough copper might not bankrupt me as my yard is small, but my property value might decrease with a copper lawn. Moreover, I would worry about the errant slug (or its family!) trapped forever under the copper sheeting.
- I could beseech the slug’s natural predators — ravens, frogs, beetles, snakes, cats, and owls — to populate my yard en masse and eat their season’s fill of these mollusks. Yet, I know how futile this mental exercise would be.
III. Act
Though slugs prefer to hang out with us in our ever-changing urban scenery, they knew a time when we didn’t drive cars — maybe we are their collective curiosities and maybe they want to know how long we can last as we alter one landscape after another. And given their aggressive nature to be Kings or Queens of the terrain they claim, I know they are sure to survive other Earthly calamities, such as the eventual extinction of the modern human.
Even so, Dan and I were determined to claim our parcel on Earth. So, in the summer of 2015, we decided to try to outwit the leopard slug. We dug out the hostas, whose large leaves had shaded the slugs from the desiccating sun. In their place, we planted ornamental grasses (which slugs abhor) and laid down jagged rocks (which slugs do not like to slide over). Instead of planting vegetables in my garden, I grew flowers that slugs dislike: coral bells, lavender, peonies, roses, and hydrangeas. I opted to grow vegetables in containers, and the yield was slightly more satisfying.
But even after that effort, the slugs lingered. In the harsh sunlight, the brick walls and tree trunks where they had slithered upon glistened like shellac. And there were holes in the leaves of my container-grown kale. One even entered our basement — probably having taken a ride on Dan’s pants legs — leaving behind a shimmery trail of slime on a black rug. We mapped its movements and saw its shriveled body at the trail’s end, near the entrance to our sump pump; it was so close to being free of our dry air.
So we bought salt and lots of it. Nowadays, before each sundown, Dan’s routine includes sprinkling salt around the perimeter of where he will be sitting for smokes during the evening hours — usually our basement steps.
We also bought plastic tongs. In spite of the salt, one or two (or more) slugs rebel and venture into the slug-free zone. That’s when he uses tongs to grab and chuck them into a neighbor’s yard.
I still freak out when I see a slug, and I seldom go outside after sundown for fear of sighting the Limax maximus. I’ve learned that I’m a coward.
While an invasive creature to the American landscape, the leopard slug is, I admit grudgingly, just trying to be. Pearce says he doesn’t know why the leopard slug likes to be around humans. I, however, will venture a metaphysical reason born out of my Hindu upbringing: karma — slugs are punishing humans for not wanting them nearby when humans are responsible for the slugs’ geophysical displacement. And I was taught to respect karma.
So I’ll only venture out into my yard at night once the frost hits. That’s when the slugs won’t be out, and it will become safe for me to enjoy the evening air, however cold.
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Sources:
Megan Paustian, PhD; Contractor at the National Museum of Natural History; Mollusk collection. April 3, 2015, and November 26, 2016. Email interviews.
Timothy Pearce, PhD; Assistant Curator and Head of the Section of Mollusks at the Carnegie Museum of Natural History. March 28, 2015. Email Interview.
Timothy Pearce, PhD. March 30, 2015. (See above for his credentials). Telephone interview.
Bland C. 2013. Why are snails and slugs are repelled by copper? Huffington Post website. http://www.huffingtonpost.com/quora/why-are-snails-and-slugs_b_3155291.html. [Published April 25, 2013.] Accessed November 30, 2016.
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Gaitán-Espitia, Juan Diego, et al. Repeatability of energy metabolism and resistance to dehydration in the invasive slug Limax maximus. Invertebrate Biology 131.1 (2012): 11-18.
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Scrap Register. Price of copper. Scrap register website. http://www.scrapregister.com/scrap-prices/united-states/260. Accessed November 30, 2016.
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http://extension.entm.purdue.edu/fieldcropsipm/insects/soybean-slugs.php. Accessed November 30, 2016.
