10 Notable Facts About Slugs

A slug is not a species but a name used to describe hundreds, maybe thousands, of species. A slug is any gastropod mollusk that lives on land and has little or no shell. Slugs with shells are called snails. The term ‘slug’ is polyphyletic. It applies to a group of living organisms linked under one name due to a common characteristic. It is not a species, as the organisms grouped as slugs do not share a common ancestor.

Slugs come in all shapes, lengths, and even colors. Given this, it goes without saying why so many people are passionate about them and even have them as pets. If you’re also interested in these amazing creatures, here are 10 incredible slug facts that will impress you!

1. Slugs Generate Their Mucus to Survive

A slug’s body is composed of approximately 80% to 90% water. As a result, it is susceptible to desiccation (extreme dryness), which is worsened by the fact that slugs have little or no shells. They keep themselves alive by generating layers of protective mucus. However, this is often not enough to ensure survival.

As such, just like snails, slugs can be seen mainly after rain. The ground is moist, and they can move freely without being exposed to temperatures that would dry them out. Slugs are found under rocks, planters, logs, and tree bark when the ground is dry. There, humidity persists, and slugs can retain their body moisture better. 

2. Slugs Generate Different Types of Mucus

Mucus is essential to a slug’s survival. Two types of mucus can be found on the feet of the slug. One type is thin, watery, and found from the center of the foot to the edges. The other is thick and sticky and spreads from the front of the foot to its back. These types of mucus are rich in fibers, which help prevent the slug from slipping on vertical surfaces.

The slug’s body mucus helps with survival in all cases. It prevents dryness and keeps the body slippery enough to escape from predators’ beaks or mouths. A slug’s body coating can also have a bad taste to deter predators further. 

3. Slugs Move at a Top Speed of 0.03 Miles per Hour

Some would add that, even if quite slippery, slugs are extremely slow. Their top speed is generally less than 0.03 miles per hour, with most slugs moving much slower. For example, some humans can walk around 20 to 30 miles daily, averaging 26.2 miles per 8 hours. A slug would need a little over six days, or 145 hours, to travel the same distance. In other words, the world is pretty much standing still for them, although this doesn’t make them any less interesting or incredible.

4. Slugs Have Four Multi-Functional Tentacles

Arguably, the most interesting body parts of a slug are its tentacles. Every slug features four of them, and all are retractable, which is why most of the time, you see only two. The tentacles are split into pairs: two are used for seeing and smelling, and two for tasting and touching.

The tentacles responsible for a slug’s sight and smell can operate independently. In short, a slug can look at you and simultaneously smell the surface it’s walking on. A slug’s tentacles are also quite sensitive, as with snail tentacles, as they quickly retract when they are touched.

5. Some Sea Slugs Can Exceed 30 Pounds

Given that slugs worldwide are not animals of the same species but share the same characteristics, it’s clear that certain species can break records in the animal kingdom. The European ashy-gray slug can grow as long as 10 inches. The largest slug in the U.S. is the banana slug, which can grow up to one foot long. You might think it’s not impressive, but imagine coming across something like that while hiking. Sea slugs, on the other hand, can get quite big. The Californian black sea hare can grow up to 39 inches long and weigh up to 35 pounds.

6. Slugs Can Be Incredible Predators

Most slugs enjoy fruits, plants, and the like. However, some would rather go on a hunt and have acquired a taste for other living organisms. The ghost slug, for instance, is known to enjoy a daily meal of worms. Sea slugs also like to hunt, with some attacking fellow slugs like Pleurobranchaea californica. Land slugs usually follow the mucus trail left by another slug when hunting other slugs. The mucus trail helps them determine whether their prey is of the same species or not.

7. Slugs Use Parts of Their Body as Bait When Escaping Predators

No, we aren’t talking about lizards whose tails drop when in danger! However, slugs have a similar strategy that they rely on when trying to escape a predator. The land slug known as the taildropper slug can amputate its tail and then flee to safety. On the other hand, some sea slugs are fitted with body parts that can snap off in dire situations. Despite this, most land slugs are not capable of self-amputation.

8. All Slugs Can Lay Eggs

Slugs are hermaphrodite animals. This means that they are equipped with both female and male reproductive organs. As a result, slugs can fertilize their eggs. Even so, some species of slugs now face extinction. This is even more worrying, considering that a slug can lay up to 500 eggs every single year.

9. The Slug’s Body is a Huge Muscle

The slug’s body, also known as the foot, is not just a succulent piece of meat targeted by predators. It is a slug’s main transportation method and a huge muscle featuring more muscles on the underside. Each of the muscles contracts when needed, forming a wave that helps the slug move forward (as the wave goes from the back to the front).

10. Slugs do not Have Bones

Slugs are mollusks, as mentioned earlier. Mollusks are invertebrate animals — they don’t have a backbone or vertebral column. Slugs, however, don’t have any bones either. During their development, slugs experience torsion. This phenomenon marks a 180-degree twisting of a slug’s internal organs. The main result is an asymmetrical body. Torsion would break a slug’s bones if it had any.