Slugs - Interesting Facts, Mucus Slime and Pest Control

Arion rufus, the red slug
Arion rufus, the red slug | Source

Slugs in Human Lives

Slugs get little respect from most people. They are usually thought of as slimy, very unappealing creatures that are annoying garden and agricultural pests. However, not all slugs are pests, and after careful observation and study a person may decide that slugs are actually interesting animals. Some people even keep slugs as pets.

Slugs produce copious amounts of slime. Many people think that the slime is gross, but it actually has some impressive properties. Researchers are investigating these properties to see if they can be helpful for us.

Should it be necessary to remove slugs from an area in order to protect plants, some type of pest control will be necessary. There are several pest control methods for slugs that are effective, safe for the environment, and in some cases, humane as well.

Arion ater, the black slug
Arion ater, the black slug | Source
External anatomy of a slug
External anatomy of a slug | Source

The Body of a Slug

A slug has a soft, elongated body. The head has two pairs of tentacles, which can be retracted. The top tentacles are longer. They have eyes at their tips that can detect light, but the eyes can’t form an image. The lower tentacles are sensitive to smells. Both pairs of tentacles are also sensitive to touch. The tentacles wave gently through the air as the slug moves, sensing the environment as it travels. The tentacles can be regrown if they're lost.

Behind the head is a fleshy lobe known as the mantle. The mantle has an opening called the pneumostome, which leads to the slug’s single lung and is used for breathing. The pneumostome is usually on the right side of the mantle.

Underneath the right side of the mantle are the genital opening and the anus. These openings aren’t located near the rear of the body, as they are in most vertebrates, because of a phenomenon called torsion. Torsion takes place in the larval stage of the slug's development. The visceral mass of the slug contains its internal organs and is twisted 180 degrees during torsion.

Slugs don’t have a single structure that can be called a brain, but they do have ganglia distributed around their body. A ganglion (the singular of ganglia) is often described as a “knot” of nerves. The ganglia of a slug are connected to each other, forming a nerve network.

The banana slug, or Ariolimax
The banana slug, or Ariolimax | Source

Diet and Life

Slugs eat fresh or decaying plant parts and fungi. They may also eat insects, worms, carrion, animal droppings, kitchen scraps and pet food. Some slugs even eat other slugs.

A slug’s mouth contains a structure called a radula, which is covered by rows of tiny and sharp teeth. The teeth are used for cutting and scraping or for grabbing hold of active prey like worms. There can be up to 27,000 teeth on a radula.

Slugs are most active at night when their surroundings are wet. Slugs may be active in winter in mild climates but hibernate if it gets too cold. Some slug species die at the end of a season, living for only a few months, but others can live for six or seven years and need one or two years to mature.

Limax maximus - the leopard slug
Limax maximus - the leopard slug | Source

Reproduction

A slug contains both male and female reproductive organs and is therefore known as a hermaphrodite. During mating, two slugs entwine, exchange sperm and then separate. The leopard slug has a very unusual mating ritual. A pair of slugs climb a tree or shrub and then lower themselves towards the ground on a string of mucus. Mating happens in midair before the slugs continue their journey to the ground. Not only do the slugs entwine, but their reproductive organs do, too.

Once sperm have been transferred from one slug to another, the sperm fertilize the eggs inside the slug’s body. A few to several hundred eggs are laid, depending on the species of slug. The eggs are generally white or transparent and are deposited in sheltered areas, such as in soil or under leaves or logs. Several batches of eggs may be produced in a year. The adult slug doesn’t guard the eggs once they're laid. The eggs stay dormant until the environment is suitable for them to hatch.

In Bornea, a green and yellow slug called Ibycus rachelae has been found to use “love darts’ when it's preparing to mate. The darts are needle or harpoon-shaped structures made of calcium carbonate. A slug releases a dart when it contacts another slug. The dart enters the second slug and injects a hormone that increases the chance of successful reproduction.

The Amazing Courtship of Leopard Slugs

Composition and Nature of Slime

Slug slime contains water, mucus and salts. Mucus is made of mucins. These are proteins with attached carbohydrates. They are able to form sticky, moisture-trapping gels when they are added to water. Slug slime is said to be hygroscopic due to its ability to absorb water. It also has the ability to change its consistency when pressure is applied and has elastic properties.

Fresh slug slime is hard to wash off our skin due to its stickiness and hygroscopic nature. Although it may be tempting to immediately reach for soap and water if we're covered with slug slime, it's actually easier to let the slime dry and then rub our hands together. The slime will form little balls that are easy to remove.

A Leopard Slug or Spotted Garden Slug

Functions of Slug Slime

The soft slug body dries out quickly if it's not protected. Slugs deal with this dilemma by secreting copious amounts of slime from skin glands, which keeps the skin moist and acts as a barrier against dessication. Even so, slugs are usually seen in damp environments rather than dry ones and are most active at night. Many slugs spend a lot of time underground.

Slug slime also plays a vital role in locomotion. The lower surface of a slug’s body contains many slime-secreting glands. The slime released by these glands allows the slug to stick to surfaces – even vertical ones – as it moves by a series of muscular waves in the body. This movement is known as adhesive locomotion. A slug sticks part of its body to the ground with its slime, uses its muscles to move its body forward and then pulls its body away from the adhesion. More slime is released and the process is repeated. Slug slime also helps prevent injury when a slug travels over rough surfaces containing stones or sticks.

A trail of glistening slug slime remains after a slug has passed through an area. The slime trail contains chemicals that can be detected by other slugs, indicating where the trail-layer has gone. This is useful if another slug wants to find a mate. In some slugs different chemicals appear in the slime during the mating season. The chemicals in the slime sometimes attract predator slugs.

Banana Slugs

Research

Scientists and engineers working in the area of robotics are very interested in the relative roles of slug slime and muscles in controlling movement. The engineers are creating experimental biomimetic robots - ones that operate according to principles discovered in animals - based on their research.

In addition, researchers are studying the properties of slug mucus with the aim of creating a similar material for human use. The mucus has the unusual characteristic of changing its consistency as a slug moves over it. Its very adhesive nature allows slugs to move over a wide variety of textures at a wide variety of angles, even while hanging in an inverted position in some cases.

Banana slugs may be bright yellow, but the species in my area is greenish yellow with dark blotches.
Banana slugs may be bright yellow, but the species in my area is greenish yellow with dark blotches. | Source

Unusual Slugs - Banana and Pink

Banana slugs are interesting and attractive animals. They are bright yellow to greenish yellow in color and sometimes have black blotches. The banana slug is the second largest slug in the world and may reach a length of almost 10 inches, although most adults are six to eight inches in length. The largest slug in the world is Limax cinereoniger, which is found in Europe and may reach a length of nearly 12 inches.

The banana slug is found in the Pacific Coast region of North America from Alaska to California. Its slime contains an anesthetic. A predator that picks up a banana slug would feel their mouth go numb and might drop the slug unharmed.

On Mount Kaputar in Australia is the strangest slug so far discovered - a bright, neon pink species known as Triboniophorus aff. graeffei. As far as is known, the species reaches a length of up to eight inches. It's thought to be related to the red triangle slug, which is found elsewhere in Australia, although it's not identical to its relative. The pink slug lives only on an isolated mountain top but is locally abundant.

Giant Pink Slugs of Australia

Pest Control

Although it’s understandable that farmers and gardeners would want to wage war on the slugs destroying their plants, many types of slugs do not attack domestic plants. Pest species can create a lot of damage, but unless slugs are interfering with human lives in some way there is no need to kill them.

Sometimes it is necessary to get rid of slugs, however, such as in cases where important plants are being killed. There are many methods of slug control, some of which are better than others. Both natural and chemical methods can be useful.

Red triangle slugs, or Triboniophorus graeffei; this species has only two tentacles instead of four, a variable background color and a distinctive mark on its back
Red triangle slugs, or Triboniophorus graeffei; this species has only two tentacles instead of four, a variable background color and a distinctive mark on its back | Source

Hand Picking

The kindest method to remove slugs and the safest method for the environment, wildlife, pets and children is to collect the slugs by hand and transport them to another place. This is the method that I use.

Attracting the slugs to a particular area would make the job of collecting them easier. Although I've never tried the technique, placing the rind of a grapefruit on the soil at night reportedly attracts slugs. People also report success when they create a shallow pit covered with a board to keep the inside of the pit humid. Slugs are attracted to the pit because of the moisture and enter it through the gap left for them.

Another red triangle slug; the marks on the Sydney blue gum tree were made by the slug's radula as it fed on the tree
Another red triangle slug; the marks on the Sydney blue gum tree were made by the slug's radula as it fed on the tree | Source

Drowning and Salting

A popular way to trap and kill slugs is to put a small quantity of beer in a container such an empty yogurt tub and then bury the tub in soil with just the rim exposed. Slugs are attracted by the odor of the beer, climb into the tub and then drown. Tubs should be cleared of dead slugs every day. Water containing sugar and yeast is said to have the same effect as beer.

Sprinkling salt on a slug also kills it. The salt draws water out of the slug, causing dehydration. This method of removing slugs is not the best from a gardener's point of view, since it increases the salt content of the soil. In addition, it's almost certainly a very unpleasant way for the slug to die.

Deroceras reticulatum, the grey field slug or grey garden slug
Deroceras reticulatum, the grey field slug or grey garden slug | Source

Creating an Abrasive Barrier

Creating a physically repellant and abrasive barrier around plants might help to control slugs. Abrasive materials that may work include coffee grounds, broken egg shells and diatomaceous earth. A large amount of barrier material arranged in a deep and wide band may be required in order to be effective, however. The University of California Integrated Pest Management Program recommends that the barrier be one inch high and three inches wide.

The caffeine in coffee grounds may act as a neurotoxin for slugs, perhaps increasing the effectiveness of a coffee barrier. Egg shells must be clean and dry before they're used. In addition, the inner membrane of the shell must be removed. Some people say that they have found coffee grounds and egg shells helpful for slug control while others say that these materials are useless. The University of Minnesota says that diatomaceous earth is moderately useful and that it "is most effective when used in dry conditions and has little effect when it absorbs moisture".

There are several problems with any abrasive barrier. The first one is the necessity to create a thick barrier in an attempt to overcome the slug's protective slime. The second is that in damp weather, when slugs are most active, the barrier material may be absorbed by the wet soil. In addition, even if it's not absorbed the material may become ineffective once it absorbs moisture. Another problem is that some barrier materials may alter the soil's properties. Egg shells raise the soil's pH, for example.

Limax cinereoniger is the largest slug on the world.
Limax cinereoniger is the largest slug on the world. | Source

Creating a Copper Barrier

The best way for a gardener to discover whether a particular abrasive barrier is helpful is to try it, following all the "rules" for its creation. There is another option, however. Copper tape or foil wrapped around plant containers, trunks or other items repels slugs and may be a better choice for a barrier than an abrasive material. The exact mechanism of the repulsion isn't known, but it's thought that the copper and components of slug slime interact to give a slug an electric shock.

How to Get Rid of Slugs

Chemical Pesticides

There are two main pesticides used to kill slugs. Both can be very effective. Iron phosphate has very low toxicity for children and pets. It's sometimes classified as nontoxic. In fact, it's used as a human mineral supplement. The EPA (Environmental Protection Agency) classifies iron phosphate as GRAS, or Generally Recognized as Safe.

Iron phosphate pellets containing tasty food for slugs as well as the pesticide are applied as bait around plants. The slugs eat the pellets, which kill them. The poisoned slugs stop feeding, hide and eventually die. Even though the chemical is considered to be safe for children and pets, I would still keep the bag of iron phosphate pellets out of their reach. Many chemicals are safe in small quantities but not safe in large amounts.

The second chemical pesticide that is commonly used for slugs is metaldehyde. This is much more toxic than iron phosphate. The National Library of Medicine lists some horrible symptoms of metaldehyde poisoning. The chemical is especially dangerous for dogs and cats. If they eat the pesticide they may die unless they are treated very soon.

Arion rufus
Arion rufus | Source

The Importance of Slugs

Many slug species play useful roles in the environment. They break down and recycle plant and animal material in the soil. They also provide food for some birds, frogs, snakes and even mammals such as raccoons. Studying the sticky mucus and movement mechanism of slugs may enable scientists to create new materials and devices with useful applications. In addition, slug behavior can be interesting to observe!

Slug Control - References and Further Information

Slug Control from the University of California Integrated Pest Management Program

More Slug Removal Ideas from the University of Minnesota

Iron Phosphate for Slug Control from the Florida Department of Agriculture

Metaldehyde Dangers from the National Library of Medicine

© 2011 Linda Crampton

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Comments 24 comments

Peter Dickinson profile image

Peter Dickinson 5 years ago from South East Asia

Always been a slug fan...thank you for your interesting and informatitive article.


A.A. Zavala profile image

A.A. Zavala 5 years ago from Texas

Fascinating hub, as always. Thank you for sharing.


AliciaC profile image

AliciaC 5 years ago from British Columbia, Canada Author

Hi, Peter. I've always liked slugs too! Thank you for your comment.


AliciaC profile image

AliciaC 5 years ago from British Columbia, Canada Author

Thank you very much for the visit, A.A. Zavala.


b. Malin profile image

b. Malin 5 years ago

I played with "slugs" as a child. This was a Wonderful Hub Alicia and kinda fun to read...and they are quite the little Hero's in the garden as well...Though their Sex Lives leaves a lot to be desired! Ha, Ha.


AliciaC profile image

AliciaC 5 years ago from British Columbia, Canada Author

Hi, b. Malin. I’ve been interested in slugs since I was a child, too. If I find any of them around my garden plants I pick them up and transport them somewhere else. I can’t bring myself to kill them!


Fossillady profile image

Fossillady 5 years ago from Saugatuck Michigan

Alicia, I have such a slug problem in my landscape. I have discovered there are certain plants they stay away from, while others, they can destroy in no time. I never really wanted to know anymore about them because they are such a nuisance to me, but i read about them anyway. They have some interesting features, i have to admit. Take Care


AliciaC profile image

AliciaC 5 years ago from British Columbia, Canada Author

I sympathize with your slug problem, Fossillady. Thank you for reading my hub, which was kind of you, considering your local slugs are such a nuisance and you don't really want to think about them!


Chatkath profile image

Chatkath 5 years ago from California

Slugs are constant little slimy visitors at my front step (cat food most likely) but I never have cared for them much and I am a die hard animal lover. (are they an animal?)

This hub is most interesting, lots that I did not know about the little creatures! :-)


AliciaC profile image

AliciaC 5 years ago from British Columbia, Canada Author

Hi, Chatkath. I guess slugs have a lot of work to do if they are going to improve their public relations! Thanks for the visit and comment.


kashmir56 profile image

kashmir56 5 years ago from Massachusetts

Hi AliciaC, thanks for this very interesting and fascinating hub,i do hate it when they leave their slime trails through my garden.


AliciaC profile image

AliciaC 5 years ago from British Columbia, Canada Author

Thank you very much for the comment, kashmir56. Slime trails are good for slugs but not for us!


thougtforce profile image

thougtforce 5 years ago from Sweden

The best way to meet your enemy is to get knowledge about them so I read this with great interest. And even if some slugs are my enemies in the garden I can´t help to admire them. They are still animals that have a purpose. You have done a great job writing a hub about this slimy creatures! And I can even like some of them:)

Voted up, useful

Tina


AliciaC profile image

AliciaC 5 years ago from British Columbia, Canada Author

You’re so right, Tina - knowledge of the enemy is important! Although I know that some slugs can be people’s enemies, other slugs play important roles in the environment. I don’t find it hard to like the slug species that leave garden plants alone, and I even find the ones that do attack gardens interesting -- and very annoying at the same time! Thank you very much for the vote.


Docmo profile image

Docmo 5 years ago from UK

What a great information filled journey through the world of slugs! Really enjoyed the biological info and the insight into slugdom. There is so much wonder in each little critter. Thanks for sharing. Voted up!


AliciaC profile image

AliciaC 5 years ago from British Columbia, Canada Author

Thank you for the comment and vote, Docmo. I agree with you - every creature is interesting in some way!


prasetio30 profile image

prasetio30 5 years ago from malang-indonesia

Very entertaining hub. Thanks for writing and share with us. I'll show this to my student. I learn much from you. Rated up! Have a nice weekend...

Prasetio


AliciaC profile image

AliciaC 5 years ago from British Columbia, Canada Author

Thank you for the comment and rating, Prasetio. I hope that you have a nice weekend too!


Peggy W profile image

Peggy W 5 years ago from Houston, Texas

Very informative hub about slugs and slug slime. I learned much from you today in reading this hub. The videos (especially the first one) were also good. Rated useful and up.


AliciaC profile image

AliciaC 5 years ago from British Columbia, Canada Author

Thank you very much for the comment and ratings, Peggy W.


andrebreynolds profile image

andrebreynolds 5 years ago

Great.. interesting.


AliciaC profile image

AliciaC 5 years ago from British Columbia, Canada Author

Thank you for the comment, andrebreynolds.


bravewarrior profile image

bravewarrior 2 years ago from Central Florida

This is fascinating! I never thought I'd want to read about slugs, much less watch a mating ritual, but this article is very educational. I know slugs are good for the garden. When I see them, I just leave them alone.


AliciaC profile image

AliciaC 2 years ago from British Columbia, Canada Author

Hi, bravewarrior. Thank you very much for the visit and the comment! I generally leave slugs alone, too. If I do need to move them I pick them up and transport them someone else. I think they are very interesting animals, although I can understand why they could be very annoying for someone growing lots of plants.

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    Linda Crampton (AliciaC)1,248 Followers
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    Linda Crampton is a teacher with an honours degree in biology. She loves to study nature and write about animals and plants.



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