Slugs are the ultimate garden pests, eager to munch on anything in their path. No fruit or vegetable plant is safe from these relentless invaders.
As frustrating as they are, slugs play a crucial role in the ecosystem by aiding in decomposition and returning nutrients to the soil. Despite their reputation, they’re more interesting—and important—than you might think.
We’ve gathered some of the most fascinating facts about slugs to show that there’s more to these creatures than meets the eye. We focused on their unique behaviors and ecological benefits, leaving out the more common garden pest complaints you already know too well.
1 – Slugs Evolved From Snails
Snails have a kind of exoskeleton in the form of a shell and have the ability to retreat inside in the face of danger or when it’s too hot and dry.
Slugs evolved from snails and lost their shells as an adaptation to their environments, which may have included high humidity and a lack of calcium. Many slugs still have a vestigial shell in the form of a leathery mantle that provides some protection.
Not all signs of the shell have vanished among the majority of slug species, however. They have a vestigial shell in the form of a leathery mantle that sits on their back. The mantle consists of a soft but leathery outer layer, with a semi-hard calcium “shell” beneath.
2 – You Can Only See 5 Percent of Slugs
Think you’ve got a bad slug problem because you can see a few hundred slugs devouring your lettuces? Well, you’re only seeing around 5 percent of the problem.
Slugs are often seen above ground, but a significant portion of their population, including both adults and juveniles, can be found underground. However, the exact percentage of slugs below ground can vary widely and is not as precisely quantified as 90 to 95 percent.
Obviously, the slug population will vary according to where you live, but to give you some idea, studies show that the average garden in the UK plays host to around 20,000 slugs.
3 – Asexuality
Slugs have both male and female reproductive organs and can reproduce through cross-fertilization with other slugs. While they can mate with themselves, it is more common for them to mate with another slug, and both slugs can lay eggs as they exchange sperm.
Slugs partially encircle one another, and then their male reproductive organs appear from beneath their mantles. The male parts of the slugs join together in a kind of corkscrew to exchange sperm.
However, they frequently get stuck like this. To become “unstuck,” one slug may chew off the reproductive organ of its partner or even its own. The slug that loses its organ can survive with just its female reproductive parts and continue to breed.
4 – 90,000 Descendants Each
A single slug lays up to 100 eggs several times each year. And bearing in mind that, mostly, when slugs mate, both get pregnant, you can see how quickly 1000s of slugs can appear. A single slug can lay thousands of eggs throughout its lifetime, leading to a large number of offspring, though not as high as 90,000.
5 – Just When You Think It’s Safe
Slug eggs are those tiny, pearly white balls you find in the soil as you dig. Small, round, delicate, and easy to squish. But they are remarkably resilient.
Slug eggs can lay dormant for years and only begin to hatch when conditions are optimal. So, even if you’re sure you’re totally on top of controlling slugs naturally, there can be thousands of eggs in your soil, just waiting for the perfect conditions.
6 – Stomach Foot
Slugs are gastropods, which means stomach foot. The foot, which is the flat bottom side of the slug, is essentially a powerful muscle.
This muscle contracts in rhythmic waves while the slug secretes the notorious slime simultaneously. This allows the slug to glide across the slime as its foot contracts.
7 – Teeth!
Yes, slugs have teeth. 27,000 teeth, to be precise. They use this ridiculous number of teeth to rasp away at their food, leaving such ragged holes in leaves. Who would think that a slug has more teeth than a shark? And, just like sharks, slugs regularly lose and replace teeth.
8 – Surprisingly Stretchy
Disturbingly, slugs can stretch to 20 times their standard length at will, making it difficult to keep them out of specific areas. They can also stretch out and wriggle through tiny holes.
9 – Green Blood
If you start skewering or decapitating slugs as a natural method of control or accidentally squish one under your boot, you’ll see that they exude green-yellowish blood. This is due to the molecule hemocyanin, which transports oxygen in slugs.
10 – They Eat A Lot
Slugs are voracious eaters, consuming up to twice their body weight in just one day. And they’ll eat pretty much anything. Like strawberries, soft fruits, veggies, and those with high water content are particularly attractive.
11. Multipurpose Slime
Slug slime is gross, but it’s crucial for the slug. Firstly, as described above, it allows them to glide their foot muscles along the ground.
A slug’s slime is as unique as human fingerprints. That’s pretty amazing. They use this uniqueness to find their way to and from shelter, particularly tasty patches of vegetation and more.
The slime is also highly absorbent, so water simply makes it more effective; hence, washing off your hands is difficult. Slime contains special fibers that make it extra sticky and help ensure slugs can make vertical climbs without sliding backward, so you may even encounter slug problems when growing in a vertical garden.
12 Mucus For Survival
Slugs are fascinating creatures of 90% water, which puts them at risk of drying out easily and exacerbated by not having shells. To prevent this, they produce protective layers of mucus. This slimy barrier is crucial but not always enough to keep them hydrated.
That’s why slugs are most active after rain when they’re at less risk of drying out and can move more easily. The rest of the time, they seek moist environments under rocks or logs to conserve moisture.
13. Slugs Are Sloooow
With a top speed of just 0.18 miles per hour, slugs will unlikely win any races against anything other than other slugs and maybe snails. In comparison, fit, healthy humans can walk at a sustained pace of around 3 miles per hour. So, if a human were to put in a full day – or 8 hours of walking – they could achieve a maximum distance of just over 26 miles (42 kilometers), whereas a slug would take 145 hours (or just over 6 days) to walk the same distance.
14. Two Pairs of Tentacles With Different Jobs
Slugs really are interesting. Yes, they’re slimy and eat your plants, but they’re incredible creatures.
Slugs have four tentacles. All of them are retractable. Probably most of the slugs you see in your yard look like they just have two tentacles, but they have four. It’s just that two are retracted.
One pair of tentacles is responsible for seeing and smelling, and the second is for tasting and touching. Isn’t that interesting? The tentacles are also super-sensitive, rapidly retracting if you lightly touch them.
Even more incredible is that the pair of tentacles for seeing and smelling can work independently from each other. So one can look at you while the other can smell the soil it’s sitting on.
15. Some Slugs Are Huge
While most slugs are quite small, some species can reach impressive sizes. The European ashy-gray slug grows up to 10 inches, while the American banana slug can reach a whole foot.
16. Some Slugs Are Useful Predators
Not all slugs stick to a diet of plants. Like the ghost slug, some prefer a carnivorous diet, hunting down worms. Some slugs will also eat other slugs. And, because most slugs are generalists, they’ll feed off carrion, helping to speed up decomposition.
17. Some Slugs Can Detach Their Tails
The tail dropper slug can detach its tail to escape a predator and then grow back the missing appendage over time. This is a fascinating evolutionary survival tactic. The slug’s predator is distracted by the tail, thinking it’s gotten its prize, while the slug makes an (albeit slow) dash for cover.
18. Slugs Are Boneless
As part of the mollusk family, slugs are invertebrates that lack bones. This boneless structure allows them the flexibility to move through tight spaces and across various terrains without the constraints of a rigid skeleton.
19. Most Active At Night
Slugs prefer the cooler, moist conditions of nighttime or rainy days for their activities. They’re less likely to venture out during sunny days to avoid the drying effects of the sun. But if you wander into your garden in mild weather at dusk, you’ll likely see an army of slugs and snails trekking out of their moist, cool daytime hidey holes.
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