You’re weeding the garden or maybe just walking barefoot across the lawn after a heavy rain when you feel it. That cold, rubbery squish. Most of us just recoil, wipe our feet, and move on with a "yuck." But if you've ever stopped to wonder what do slugs do to humans beyond just being gross, the answer ranges from "absolutely nothing" to "surprisingly dangerous."
Slugs are basically snails that lost their shells through evolution. They’re gastropods. They aren't aggressive, they don't have stingers, and they certainly aren't hunting you down. Yet, in the world of biology, being "harmless" is a relative term. They carry a heavy load of mucus and, sometimes, microscopic hitchhikers that can genuinely change a person's life in ways you wouldn’t expect.
The Slime Factor: Is It Just Gross?
Most people's primary interaction with a slug is the slime. Slug mucus is a marvel of engineering—it’s a liquid when the slug moves but turns into a solid-like grip when they need to stick to a vertical wall. Honestly, it's incredible. But for humans, getting that slime on your skin is mostly just an annoyance.
Slug slime is non-toxic to the touch. You won't break out in hives just because a common garden slug crawled over your hand. However, it is incredibly difficult to wash off. Because it’s hygroscopic (it absorbs water), trying to rinse it away often just makes it expand and get more slippery. You’ve probably noticed that. You need soap, friction, and a bit of patience.
There is one specific nuance here: some people with extremely sensitive skin or mollusk allergies might experience mild contact dermatitis. It’s rare. Usually, the "damage" is purely psychological. You feel dirty. You want it off. That's about it for the average backyard encounter.
The Real Danger: Rat Lungworm Disease
Now we have to talk about the scary part. This isn't to be alarmist, but it’s the primary reason people ask what do slugs do to humans from a medical perspective. Slugs can act as intermediate hosts for a parasite called Angiostrongylus cantonensis, commonly known as rat lungworm.
The cycle is fascinating and a bit grim. Rats poop out the larvae, slugs eat the poop, and the larvae develop inside the slug. If a human eats that slug—or eats unwashed lettuce that a slug crawled over and left larvae on—those parasites can end up in the human brain.
The Case of Sam Ballard
This isn't a "medical mystery" myth. You might remember the tragic story of Sam Ballard, a young rugby player in Australia. In 2010, on a dare at a party, he swallowed a garden slug. It sounds like a harmless teenage stunt. It wasn't. He contracted rat lungworm disease, fell into a coma for 420 days, and was left paralyzed until he passed away years later.
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This is an extreme example. Most people don't go around eating slugs on purpose. But it highlights the stakes. When the larvae enter a human, they often head for the central nervous system. Because humans aren't the intended host (the parasite wants to be in a rat), the larvae get lost and die in the brain or spinal cord. The resulting inflammation causes eosinophilic meningitis.
Symptoms can include:
- Intense headaches that don't go away with aspirin.
- Neck stiffness.
- Tingling or "pins and needles" sensations on the skin.
- Low-grade fever.
- Sensitivity to light.
Can Slugs Bite You?
Technically, yes. But not in the way a dog or a spider does. Slugs have a "radula." Think of it like a microscopic chainsaw tongue with thousands of tiny chitinous teeth. They use it to rasp away at leaves, fungi, and sometimes decaying meat.
If a large slug, like a Great Grey Slug (Leopard Slug), sits on your hand for a long time, it might start "tasting" you. You’ll feel a weird, rasping sensation. It might even manage to scrape off the very top layer of dead skin. It doesn't really hurt. It’s more of a tickle or a tiny scratch. They aren't trying to eat you; they’re just exploring their environment with their mouths. They don't have the jaw strength to "bite" a chunk out of a human.
Parasites Beyond the Lungworm
While rat lungworm is the headline-grabber, slugs can carry other nasties. They are scavengers. They eat animal feces. They eat rotting carcasses. Because of this, their bodies can be covered in Salmonella, E. coli, or Listeria.
If you handle a slug and then immediately eat a sandwich without washing your hands, you’re essentially playing Russian roulette with food poisoning. This is particularly important for toddlers. Kids are curious. They pick things up. Sometimes they put them in their mouths. In 2023, health departments in the Southeastern U.S. issued reminders to parents to keep an eye on toddlers in gardens specifically because of the risk of accidental ingestion of gastropods and their trails.
The Myth of the "Poisonous Slug"
In North America and Europe, there are no "poisonous" slugs that will kill you just by touching them. However, some slugs have evolved to be unpalatable. They produce chemicals in their mucus that taste bitter or cause a numbing sensation to predators like birds or frogs.
If you were to lick a slug (please don't), your tongue might feel a bit numb or tingly. This is a defense mechanism. It’s not meant for you; it’s meant for the robin trying to turn the slug into breakfast.
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What About Your Pets?
When we ask what do slugs do to humans, we often overlook our "furry humans"—our dogs. Dogs are much more likely to eat a slug than we are. In dogs, the lungworm parasite doesn't go to the brain; it goes to the heart and lungs, causing severe respiratory issues and blood clotting problems. If you have a dog that "grazes" in the yard, slugs are a genuine veterinary concern.
How to Stay Safe Around Slugs
You don't need to live in fear of your garden. You just need a bit of common sense.
- Wash your produce. This is the big one. Slugs love hiding in the nooks and crannies of kale, romaine, and cabbage. Even if you don't see a slug, the microscopic larvae can be in the slime trails left behind. A vigorous rinse under cold water is usually enough to dislodge them.
- Wear gloves. If you're a heavy-duty gardener, wearing gloves prevents the slime from getting under your fingernails and reduces the risk of any bacteria entering small cuts on your hands.
- Teach the kids. Make sure children know that slugs are "look but don't touch" (or at least "don't lick") creatures.
- Copper barriers. If slugs are overrunning your porch or patio, copper tape is a great non-toxic deterrent. It gives them a tiny, harmless "electric shock" sensation that makes them turn around.
Slugs play a vital role in our ecosystem. They are nature’s clean-up crew, breaking down organic matter and turning it into nutrient-rich soil. They aren't villains. They’re just messy roommates who happen to carry some baggage.
Essential Actionable Steps
If you’ve had a close encounter with a slug or are worried about the ones in your garden, here is exactly what you should do:
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- After handling: Wash your hands with warm, soapy water for at least 20 seconds. Use a nail brush if you’ve been digging in the dirt where they live.
- For the garden: If you have an infestation, use iron phosphate-based slug pellets. These are generally considered safe for pets and wildlife, unlike older metaldehyde baits which are highly toxic.
- In the kitchen: Never eat raw "wild" greens without a thorough wash. If you’re in a region where rat lungworm is endemic (like Hawaii, parts of the Gulf Coast, or Southeast Asia), consider cooking your greens, as heat kills the parasites.
- Medical attention: If you know for a fact someone has ingested a slug, contact a doctor or poison control immediately. Don't wait for symptoms to appear, as early intervention is key for managing potential parasitic infections.
Slugs are fascinating, slimy, and mostly harmless—as long as they stay in the garden and off your plate. Keep your hands clean, your lettuce washed, and your curiosity at a safe distance.