Anyone who’s owned an aquarium knows how wonderful snails are. Conversely, anyone who’s owned plants knows how frustrating slugs are. Today we’re going to look at these little monsters and how to get rid of them.
But more importantly, we’ll examine prevention methods and get to know more about slugs. You might be surprised by just how odd they really are.
Identifying Slug Damage
Think something’s munching on your plants but can’t catch the offender? Slugs are nocturnal vandals, so you’ll need to recognize their calling cards to confirm you’re dealing with these slimy saboteurs.
The most obvious sign is the silvery slime trails. These shiny paths catch the morning light and can be found on plants, garden furniture, and walkways. It’s literally their signature move.
Look for irregular holes in leaves, often in the center rather than edges. Unlike caterpillars that munch from the sides, slugs prefer to dive right into the middle of leaves. They’re especially fond of tender young seedlings and can demolish them overnight, leaving nothing but stems.
Check for damage low to the ground as slugs rarely climb high unless they’re particularly ambitious. Fruits and vegetables sitting on soil are prime targets, with strawberries, tomatoes, and lettuces being particular favorites. You’ll find unsightly gouges and cavities that ruin both appearance and edibility.
If you’re still not sure, try the flashlight test. Head out to your garden after dark with a flashlight and you might catch them in the act. Just remember to check the undersides of leaves and around the base of plants where they like to hide during their midnight feast.
Getting Rid of Slugs
Depending on the severity of your infestation, eliminating these critters can either be quite easy or extremely frustrating. Thankfully, there’s a wide range of things you can try, so if one method doesn’t work, just experiment a bit.
Slug Bait
You’ll want to get a good organic bait if going this route. Organic slug bait is usually made with iron phosphate, which is relatively safe around children and pets in small quantities. Sluggo and Garden Safe are two popular brands that actually work.
Just like any poison bait, follow the package instructions carefully. Spread the bait granules out and the slugs will consume it, poisoning them. Meanwhile iron phosphate is good for plants and the bait will slowly absorb. Avoid baits containing metaldehyde.
Beer Traps
This is a great choice if you don’t mind the smell of a dorm bathroom right after a weekend frat party. Take a couple small empty containers with an inch or so of beer in each and bury them so just the opening is visible. Make sure that opening is large enough for a slug to comfortably fit.
The slugs will smell fermentation and go after the beer, drowning in the process. Check your traps each morning and remove any corpses. Just be warned, this trap can be almost as memorable as ladling out homemade garum.
Employ Natural Predators
Just about everything out there likes to eat slugs, from birds to lizards, frogs and snakes to ground beetles, fireflies, and ants. Making your yard or garden more hospitable to these critters can give you some valuable allies.
Just make sure the critters you attract won’t become pests in their own right.
Pluck Them Up
Throw on a pair of gloves and simply grab the slugs as you see them. You can place a damp piece of wood out for them to retreat to or snatch them in the act of eating your plants.
Once you have them, it’s up to you if you wish to release them somewhere else, drop them in a bucket of soapy water, or feed them to the birds.
Coffee Grounds
Those used coffee grounds are amazing for your garden. They have a neutral 6.5 pH and add nitrates to the soil. This feeds beneficial nematodes that would otherwise compete with your plants for soil nitrogen. But even better, slugs dislike the smell and will often avoid areas where coffee has been spread.
Eggshells
Next time you make some eggs, boil the eggshells and let them steep overnight. The resulting water is a great source of calcium for your plants. But even better, you can sprinkle the broken shells around your plants. The sharp edges are quite painful to the slugs, and the shells will decompose to add even more calcium to the soil.
Note you can use unboiled eggshells, but be sure to rinse them well before crushing so they don’t stink and attract other pests.
Grapefruit Traps
Cut a grapefruit in half and remove all the pulp so only the half rinds are left. Place these by targeted plants to create little dome shelters. Slugs and other pests will hide inside them overnight.
Come morning, slip a piece of paper under the dome and remove the trap and its contents. You can dispose of it or sit it out as a bowl feeder for birds to devour its prisoners.
Salt
The rumors are true! Salt, when sprinkled on a slug, will draw the water from its body, causing a rather painful death through dehydration. Unfortunately, you have to be careful where you use the salt, as getting any on the soil around your plants can harm them too.
If you must use this line of attack, try to do so on a sidewalk or table.
Preventing Slugs
There are a few good ways to deter slugs from your plants or redirect them. Here are a few good ones, as well as a bonus method that doesn’t work despite being promoted frequently.
Repellent Plants
Plants that have strong scents or are otherwise deemed inedible to slugs can be used to discourage them from attacking your more precious plants. Some great examples include:
- California poppy
- Day lilies
- Fennel
- Ferns
- Foxglove
- Fuchsia
- Geranium
- Hydrangea
- Lavender
- Nasturtium
- Rosemary
- Sage
- Snapdragon
Simply plant these around your more vulnerable plants. The slugs will be less likely to wander past them to discover the tastier treats beyond. A few sacrificial plants outside of this protective ring makes this defense even more effective.
Be warned that slugs will still go after these plants when they’re tender seedlings, so give them some protection until they mature or transplant adult plants to your garden.
Sacrificial Plants
Sometimes the best way to deter a pest is to redirect it. Sacrificial plants are just that: plants you add to the edges of your garden specifically to lure in pests so they can be disposed of.
Marigolds are a popular choice for slugs (and the repel many other pests). You can either pluck the slugs from your marigolds or destroy the whole plant if it catches a decent number of pests.
Just be sure a sacrificial plant is furthest out from your vulnerable plants. When paired with repellent plants, your garden will be almost impenetrable.
Sand
If you’ve ever had to run barefoot on a rocky path, you’ll probably know why slugs – like Anakin – hate sand. Sprinkle it around your plants and only the hungriest of slugs will bother trying to cross it. As a bonus, the sand will also help keep the soil retain moisture longer.
Vaseline
While slugs may think they’re slick, that’s nothing compared to a plant pot with a layer of Vaseline on it. If the slug can’t reach the plant, it can’t feed on it.
Bonus Myth: Copper
There’s an old wives’ tale that says putting copper bands around your flowerpots will stop slugs. According to this story, the copper shocks the slug as it tries to cross the barrier. Unfortunately copper wire alone won’t create an electrical charge, so this method tends to have no effect.
Getting to Know Slugs
Outside of being slimy and popping up often after it rains, the average person knows very little about slugs. That’s a pity, because they have a lot of interesting and strange quirks.
Some Fun Facts
- Despite popular belief, slugs and snails are related but differ in more than just the presence of a shell. Both are terrestrial mollusks in the Class Gastropoda. The term “slug” is often generically to those without a shell and “snail” refers to those with a shell.
- Oddly enough, slugs are a result of convergent evolution and retain some vestige of a shell, usually internally. They come in a variety of shapes and sizes.
- Much like snails, some cultures enjoy eating slugs.
- All slugs are true hermaphrodites, meaning they have both male and female gonads that are fully functional. Unlike humans and other animals where full or pseudo hermaphroditism (where only one set of gonads is functional) is very rare, there is no such thing as a male or female slug. However, this does not mean a slug can impregnate itself, which is a common myth.
- Another common myth is that slugs fight for dominance while mating by mutilating each other. Very few species (all but one are banana slugs) are known to bite the male genitalia off of their partner (or themselves), and it occurs when the genitals have become stuck during copulation. A slug suffering such an indignancy may still copulate with its female genitals afterwards.
- Rounding out these fun facts is the multiple uses of mucous. Slugs produce different types of mucous. One type protects their bodies, making them harder for birds to hold onto and sometimes tastes bad. Another is used to aid propulsion. A slug can tell if a slime trail is from another of its species and follow it for mating.
Time of Year/Weather Conditions
If you’re waging war against slugs, knowing when they’re most active gives you a tactical advantage. These mucus-covered pests aren’t fans of all seasons equally.
Spring
Spring is prime slug season. As temperatures warm up and spring rains create moist conditions, slugs emerge in force. This unfortunately coincides with when you’re planting tender new seedlings (a slug’s equivalent of an all-you-can-eat buffet). Be extra vigilant from March through May.
Slugs thrive in damp conditions regardless of season. After a good rain is when you’ll see peak slug activity, especially at night when temperatures are mild (between 50-70°F or 10-21°C). If you’ve had consistent rainfall for several days, prepare for a slug explosion.
Summer
Summer brings a brief reprieve during hot, dry spells when slugs retreat underground or into shady, moist hideouts. But summer thunderstorms will quickly bring them right back to the surface.
Fall
Fall sees another surge in activity as temperatures cool and rainfall increases. Those preparing fall gardens should be on high alert, especially when planting leafy greens that slugs find irresistible.
Winter
Winter isn’t necessarily slug-free, particularly in milder climates. On warmer winter days, slugs can still emerge to feed, though they’re generally less active.
For maximum effectiveness, time your anti-slug measures with their activity patterns. Apply controls in early spring before populations explode, and reapply after heavy rains when slugs are most active. Early evening applications work best since you’ll catch them just as they’re emerging for their nightly feast.
A Slug’s Diet
Slugs generally prefer fungi, decaying plant matter, or are carnivores that feed on other slugs and earthworms. However, this doesn’t mean that slugs won’t feed on the leaves of living plants or even fruits and vegetables, especially if a preferred food source isn’t available.
Common plant targets include:
- Apple
- Basil
- Beans
- Cabbage
- Carrot
- Chrysanthemum
- Cucumber seedlings
- Daisy
- Dahlia
- Hollyhock
- Hosta
- Kale
- Lettuce
- Lily
- Lobelia
- Marigold
- Peas
- Petunias
- Primrose
- Squash/Zucchini
- Strawberries
- Tomatoes
- Tuberous begonias
Are Slugs Dangerous?
For the most part, slugs are harmless to handle. However, they can carry parasites, including rat lungworm in certain regions (mainly Pacific islands, parts of Asia, and some southern areas), which can cause meningitis if slugs are accidentally consumed on unwashed produce.
Some slug species also secrete irritating substances when threatened. Beyond human health concerns, several species are considered significant agricultural threats due to their voracious plant consumption.
Morgan is a certified entomologist and pest control consultant and a member of the National Pest Management Association.
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