What are Slugs? How to get rid of the animal slugs

What are Slugs?

Slugs (or Land slug) are terrestrial gastropod mollusks that do not possess shells or have very reduced or small internal shells. In case you’re wondering, mollusks are those soft-bodied animals that inhabit damp environments such as the common snail. Slugs are very similar to snails but have coiled shells that are large enough for them to retract their soft body into.

The term slug is generally used for apparently shell-less mollusks like the land slug, sea slugs, and semi slugs. This article is based solely on the land slugs which are terrestrial and not aquatic like the sea slug. The categorization “slug” is polyphyletic because their shell-less condition was derived from more than one common evolutionary ancestor or ancestral group and thus are not suitable for placing in the same taxon.

Slugs have both female and male reproductive organs and therefore are hermaphrodites. For fertilization and reproduction to take place, a slug has to locate a mating partner. Once these animals locate a mating partner, they encircle each other in a phase of courtship.

Then, sperm is exchanged through their protruded genitalia. Few days after mating, the slugs lay an estimated amount of 30-75 translucent eggs. They can lay their eggs under the cover of a fallen log or other objects, and even in a hole in the ground. Apart from finding a suitable hiding spot for their eggs, the adult slugs render no further care for their eggs and abandon them. The adult slugs can mate and lay eggs throughout the year.

Slugs feed on any kind of foliage but usually do the most damage to tender leaves and seedlings’ stems, thus, they are seen as a nuisance by most garden growers. In as much as slugs could be a nuisance in the garden causing damages to fruits and vegetables, they have some importance. In actuality, a small population of slugs is good for the garden as they break down garden debris, thereby turning it into nitrogen-rich fertilizer which enhances the nutrient in the soil.

Where do slugs come from?

The majority of slugs evolved and came from snails that have an external shell made up of calcium and other minerals.  Over time, these slugs lost part or all of their shell. However, some slugs kept possession of a remnant shell beneath a soft outer mantle.

According to the hypothesis, it is stated that in damp temperate regions, unavailable calcium and a damp environment contributed to the gradual loss of the slug’s shell. A snail can retract into its shell when the weather is hot and dry in order to prevent desiccation. Whereas, a slug has to enter the soil or go under vegetation to prevent themselves from desiccation.

Slug habitat

The slug naturally loves and lives in damp or dark habitats. Their choice of damp habitats is related to the nature of their body. Since they have damp bodies, they can easily get dried out and so require a wet habitat. Usually, you commonly see them in gardens and sheds. Anywhere around the world, as far as the environment is damp and cool, a slug is likely to be seen there.

What do slugs eat?

It is fair enough to say slugs are omnivorous animals as they can eat almost anything. Many of them are generalists and feed on varieties of organic materials e.g lichen, the leaves of plants, mushrooms, and even carrion. Also, some slugs are predators feeding on earthworms, snails, and other slugs.

The slugs that are herbivores feed on a wide spectrum of herbs, flowers, fruits, and vegetables. Also, they feed on cabbage, apples, peas, and carrots as a sole food source. Common examples of flowers that these slugs eat are primroses, petunias, tuberous begonias, hollyhocks, chrysanthemums, daisies, narcissus, lilies, daffodils, gentians, lobelia, and irises.

Some slugs are fungivores e.g are families like the Philomycidae and Ariolimacidae. Slug species that belong to these families feed on mushrooms and slime molds. For example, Philomycus carolinianus and Phylomicus flexuolaris eat slime molds while Ariolimax californianus feed on mushrooms (basidiomycetes).

The species of mushroom used as food sources are milk caps, Pleurotus ostreatus, Lactarius spp., the oyster mushroom, and the penny bun (Boletus edulis). Also, other mushroom species eaten are Agaricus, Pleurocybella, and Russula. The Slime molds used as food sources are Stemonitis axifera and Symphytocarpus flaccidus. Nevertheless, some slugs are selective about the particular developmental stages or part of fungi they eat.

Anatomy and Physiology of Slug

Mantle

There is a saddle-shaped mantle that is positioned on top of the slug, behind its head. Under the mantle are the anus and genital opening with the respiratory opening on one side of the mantle which is easily seen when open, but hardly seen when closed. This opening is called the pneumostome. The single lung of the slug opens externally through the pneumostome and this opening is heavily vascularized to allow gas exchange.

Tentacles

Many land slugs like other land gastropods have two pairs of tentacles on their head that are retractable. The upper pair of tentacles called optical tentacles serves as a light sensor and at its ends are eyespots. Whereas, the lower pairs of tentacles called oral tentacles provides a sense of smell and are used to detect chemicals. The tentacles of a slug can retract and extend in order to avoid damage. However, if their tentacles get bitten off by a predator, they can grow a new one.

Tail

The tail of the slug is behind the mantle and some species have a ridge called the keel. This keel is a prominent ridge that runs over the slug back along the middle of the tail. Sometimes, the keel runs along the whole tail of the slug or along only the final part of the tail.

Foot

The foot of the slug is the flat bottom side of the slug. Slugs movement like almost all gastropods is controlled by the muscular contraction on the underside of their foot. As they move, they simultaneously secrete a layer of mucus that it moves on. This actually helps to avoid tissue damage to their foot. In some slugs, there is a structure called the foot fringe around the edge of the foot.

Vestigial shell

Most slugs have an internal shell that serves as a storage organ for calcium salts. This organ is usually in conjunction with the digestive glands to carry out its storage function. An internal shell is a remnant of their shell that was retained and such anatomy is seen in the Limacidae and Parmacellidae. However, some slugs lack shells such as the Adult Philomycidae, Onchidiidae, and Veronicellidae.

Slug teeth

Like other mollusks, slugs have a flexible ribbon-like anatomical structure covered in rows of microscopic teeth called a radula that is used for feeding. They have approximately 27,000 microscopic teeth (denticles). The radula serves as a circular saw that cuts through vegetation and chops it as they go. When the teeth of the slug wear out, they grow new rows of teeth that replace the worn-out ones.

The radula is sometimes compared to a tongue. Its main function is typically scraping or cutting food before the food enters the esophagus. Herbivorous and carnivorous slugs use radula for feeding.

Slug body physiology

The bodies of slugs are made up mainly of water and since they don’t have a full-sized shell like the snail they are very prone to desiccation. Hence, in order to survive, they have to generate protective mucus. Their choice of inhabiting damp habitats is related to the nature of their body. This is why when it rains you see many species being active as a result of the moist ground.

Then, in order to retain their body moisture in drier conditions, they have to hide in damp environs such under rocks, planters, tree bark, and fallen logs. Slugs during development undergo torsion like other gastropods. Torsion is a 180 degree twisting and rotation of the internal organs. Internally, the anatomy of the slug shows the effects of this torsion. Whereas, their external features appear more or less symmetrical, with an exception to the pneumostome, which is on one side of the animal, usually the right-hand side.

Body mucus

There are two types of mucus that these slugs produce:

1. Thin and watery mucus
2. Thick and sticky mucus

These two mucus types are hygroscopic. The thin mucus spreads from the center of the foot to its edges, while the thick mucus spreads from the front of the foot to the back. Also, they produce and coat their body with thick mucus.

The reason these animals don’t slip down vertical surfaces is that the mucus the foot secretes contains fibers. These fibers prevent them from sliding down when climbing vertical surfaces.  The mucus secreted has a secondary effect aside from preventing damage to the foot. This secreted mucus leaves a slime trail that other slugs recognize when they come across it. They can recognize the slime trail produced by one of their same species and use it to find a mate. Also, some carnivorous slugs as part of their hunting behavior follow the slime trail.

Furthermore, the body mucus of the land slug provides some protection against predators. The mucus can make them hard to half and pick up. For instance, a bird’s beak will find it hard to pick up and hold the slug when harden or may even find the mucus distasteful. Additionally, some slugs can produce very sticky mucus which can immobilize and trap predators within the secretion. During copulation, some slug species secrete slime cords to suspend the pair mating in the air e.g Limax maximus.

How do slugs behave?

A slug can contract its body when attacked to make its body harder and more compact, still, and round. This behavior makes them become firmly attached to the substrate. Thus, them making their body hard together with their slippery mucus, makes it difficult for predators to grasp them. Moreso, the taste of the mucus is distasteful and a deterrent.

These animals can also immobilize their predators by producing highly sticky and elastic mucus that can trap predators. When attacked, some species like the Kerry slug exhibit response behaviors that are different from the general behavioral pattern of slugs. The Kerry slug usually retracts its head and letting go of the substrate, it rolls up completely. It stays contracted in a ball-like shape and this behavior is unique among all the Arionidae and most other slugs.

Interestingly, some slugs exhibit autotomy and self-amputate a portion of their tail in order to escape from a predator. Some slug species even adopt hibernation during the winter and hibernate underground in temperate climates, whereas the adults in other species die in the autumn.

There are documented intra-specific and interspecific agonistic behavior that varies greatly among slug species. When competing for resources, slugs usually resort to aggression. Seasonality also influences this aggressiveness because as a result of climatic conditions the availability of food and shelter may be compromised. Thus, during the summer slugs are prone to attack as the availability of resources is reduced. Moreso, the aggressive responses during winter are substituted by a gregarious behavior.

How do slugs reproduce?

Slugs have both female and male reproductive organs and therefore are hermaphrodites. For fertilization and reproduction to take place, a slug has to locate a mating partner. Once a mating partner is located, the two slugs encircle each other, and sperm is exchanged through their protruded genitalia.

Finding a mate

Land gastropods such as slugs and snails have no sense of hearing and their vision is limited. As a result, they depend totally on chemoreception, tactile perception, and primarily olfaction. Finding a mate is influenced greatly by airborne chemicals.

Usually, slugs raise their head once they detect pheromones in the air and orient themselves towards the direction of the perceived pheromone. Many of them locate their mating partner also by mucus trail-following. The mucus trail-following can make up a major part of precourtship behavior and may be an alternative strategy to airborne cues.

Finding a mate using mucus trails requires the discrimination between heterospecific and conspecific trails. Therefore, it is preferable for slugs to incorporate species-specific cues into their trails to ease finding a mate. For instance, in some species like the banana slugs (Ariolimax), together with their mucus, they secrete pheromones to attract a mate.

Also, it is possible for the slug following the slime to carry out a quality assessment of a potential mate based on its mucus trail. The mucus of a slug can reveal information on its body size or where it is infected by a parasite which can give an insight into the species ability to produce an abundance of offspring. A larger size mucus can suggest that the slug is highly fertile, while parasitism (being infected by a parasite) could indicate it suffers from low egg production or sterility.

Courtship

Once these slugs find a mating partner, they undergo a prolonged phase of courtship before copulation. This phase of courtship may last for several hours with these two slugs encircling each other with their heads towards each other’s tails.

They crawl in a clockwise direction in a way that their right sides that contain the genital pores continue to face each other. This circling is probably to assess if the other slug is ready to mate. As courtship progresses, the speed of encircling each other decreases.

Progressively, they lie close together staying in the antiparallel configuration as each of them protrudes a sarcobelum from its genital pore. Sarcobelum is a highly maneuverable penile structure that the slug uses to stroke its mate. During the mutual stroking, sarcobela probably transfers secretions from the glandular part of the penis wall.

Love darts

Shooting calcareous or chitinous love darts occurs in some species of land slugs. In the final stages of courtship, they shoot love darts into each other’s bodies. However, the only species that bear darts are those that mate face to face in a simultaneous reciprocal manner.

In mating, the two slugs shoot at each other unless a dart is unavailable. The dart is usually regenerated after a recent mating and it may happen to be unavailable in the next mating. Actual mating takes place after dart shooting.

Mating

This is the phase where sperm is transferred. This period involves the duration of penis eversion to when the genitalia loses contact with the other slug. Amongst slug species, this period of mating varies, although what is common among them is the sudden eversion and very brief sperm transfer. The transfer of sperm can be unilateral or simultaneously reciprocal, and external or internal. Moreso, the received sperm is either used for egg fertilization or is digested.

Few days after mating, the slugs lay an estimated amount of 30-75 translucent eggs. They can lay their eggs under the cover of a fallen log or other objects, and even in a hole in the ground. Apart from finding a suitable hiding spot for their eggs, the adult slugs render no further care for their eggs and abandon them. The adult slugs can mate and lay eggs throughout the year.

Apophallation

Interestingly, a mating behavior known as Apophallation (biting off of the penis) has been reported only in one species of Deroceras and some species of a banana slug. Sometimes, in the banana slug, the penis gets trapped inside the mating partner’s body. As a result, Apophallation enables the slugs to separate themselves by either one or both of them chewing off their own penis or the other’s penis. However, the penis being discarded is not the end of their reproductive life because as hermaphrodites, the banana slugs are still able to mate using only the female parts of their reproductive system.

Types of Slug

• Leopard slug
• Banana slug
• Black slug
• Tawny garden slug
• Kerry slug
• Toga mantle slug

Leopard slug

The leopard slug (Limax maximus) is literally the biggest slug. This slug species is also known as the great grey slug.  They belong in the family Limacidae (keeled slugs) and are among the largest keeled slugs, with the species Limax cinereoniger being the largest. Limax cinereoniger, being the largest slug can grow up to 30 cm (12 in) in length.

Leopard slug is a species of the genus Limax. Their adults grow about 10-20 cm in length. Generally,  they have a light greyish or grey-brown appearance with darker spots and blotches. However, the patterns and coloration of their body vary amongst this species.

These slugs have an unusual and distinctive mating method. When mating, the pair of slugs hang suspended in the air using a thick thread of mucus. You may see them hanging from a tree branch or other structure. Leopard slugs are native to Europe but have been accidentally introduced to several other places around the globe.

Banana slug

These slugs ( Ariolimax columbianus) are usually bright yellow, hence, their nomenclature. However, some of them may be also greenish, brown, tan, or white. However, the banana slug sometimes looks almost entirely black because of its black spots that are so extensive. With changes in food consumption, moisture levels, and light exposure, individual slugs will change colors. Moreso, their color may indicate the age of the slug and distinguish a healthy or injured slug. The banana slug can live within an average of 1-7 years.

Amongst the terrestrial slugs in the world, the Pacific banana slug is the second-largest species and can grow up to 25 cm (9.8 in) in length weighing about 115 grams (4.1 ounces). These slugs can move at 17cm per minute and are endemic to the forest floors along North America’s Pacific coastal coniferous rainforest belt.

The positioning of the pneumostome on the mantle of the banana slug helps to distinguish the species of Ariolimax. Furthermore, the slime of the banana slug contains pheromones that attract other slugs for mating.

Black slug

The black slug (Arion ater L.) is also called black arion, large black slug, or European black slug. A black slug is a large terrestrial gastropod mollusk that belongs in the family Arionidae (round back slugs). These land slugs like other slugs and terrestrial mollusks lack shells.

Most times Slugs function as decomposers and are also omnivorous; the black slug is one such slug. It decomposes organic matter, preys on other organisms, and consumes vegetative matter. They are endemic to Europe and are an invasive species in Australia, Canada, and the United States.

Tawny garden slug

The tawny garden slug (Limacus flavus) is also known as the cellar slug or the yellow slug. It is a medium-to-large species of land slug in the family Limacidae. The tentacles of these species are pale blue and their body is yellow with grey mottling. Also, the body length of these slugs when extended can reach 7.5-10 cm (3.0-3.9 in). These slugs are common in Wales,  England, Ireland, Scotland, and most of southern and western Europe. Also, in many other parts of the world, it has been accidentally introduced such as in Great Britain, Ukraine, and China.

These slugs make use of two pairs of tentacles on their heads like many other land slugs to sense their environment. They use their optical tentacles to sense light and their oral tentacles for the sense of smell. The yellow slug as all slugs moves relatively slow. It glides along utilizing a series of muscular contractions on the underside of its foot and leaves a slime trail behind as it lubricates the foot with mucus.

Kerry slug

The Kerry slug (Geomalacus maculosus) which is also known as the Kerry spotted slug is a species of land slugs. It is medium-to-large in size in the family of Arionidae (round back slugs). Kerry slugs are dark grey or brown in color with yellowish spots.

Generally, in length an Adult Kerry slug measure about 7–8 cm (2.8–3.2 in). These slugs have internal anatomy that has some unusual features that are different from the genus Arion, which is also part of Arionidae.

These slug species are found in County Kerry in the southwest region of Ireland. Also, they are more widespread in north-western Spain and central-to-northern Portugal. It is said that these species have a lusitanian distribution (a type of disjunct distribution) because they have been far recorded exclusively at locations in Ireland and north-western Iberia. They tend to require environments that have warm summer temperatures, high humidity, and acidic soils with no calcium carbonate.

Kerry slugs are mostly nocturnal or crepuscular but are active in Ireland on overcast days. They eat fungi, mosses, lichens, and liverworts that grow on tree trunks and boulders. These slug species in 3 countries are protected by conservation laws. However, they are now known to depend less on sensitive wild habitats than when these laws were introduced.

Toga mantleslug

The Toga mantleslug (Philomycus togatus) is a species of land slug that belongs to the Order Stylommatophora in the family Philomycidae. These slugs are large and are distinguished by their pink foot edge and orange mucus. The mantle of the toga slug covers its entire back and has a speckled stripe on top. This mantle is darker on the lower sides. Toga mantleslugs are common in Pennsylvania and they can be seen crawling on tree trunks or logs during wet summer weather in mature forests. Presumably, they eat algae and fungi.

These slugs as part of their mating behavior use love darts which is a calcium carbonate spike located in a sac to aid in reproduction. The dart is shot into a potential mate, thus, injecting pheromones probably to help with species recognition. Though the dart does not detach and it is not directly involved in the transfer of sperm.

How to get rid of slugs

• Sprinkle salts on slugs
• Create a barrier
• Remove garden debris
• Use companion plants to increase the natural predators of slugs
• Remove slugs manually
• Plant trap crops
• Use beer traps
• Make use of the grapefruit trap

Slugs in the cool wet soils of spring can destroy early fruits and young seedlings overnight. They feed on any kind of foliage but usually do the most damage to tender leaves and seedlings’ stems. This can be so disheartening to garden growers and thus they try to manage the slug population to avoid further damage. Here are few ways one can get rid of slugs in the garden or home:

Salt on slugs

Applying salts on slugs usually kills them and this can be explained by the scientific principle of osmosis.  Osmosis takes place when molecules of a solvent tend to pass from a less concentrated solution through a semipermeable membrane into a more concentrated one. This results in a homogenous mixture of two (or more) substances in which the solute, is dissolved in the solvent.

In the case of salt and slugs, when the solution meets on both sides of the slug skin (permeable membrane), the solvent can pass through the membrane. In osmosis, to even out the concentration, solutions usually pass to the side with more solute.

The cells of slugs are all water trapped inside a permeable membrane and if salt is sprinkled on the slug, the salt crystals will definitely mix up with the water in the mucus of the slug. This forms a salt-water solution, although this new solution now has a higher salt content compared to that of the water in the cell of the slug. Trying to even out things, the water from the cells of the slug is extracted to join the salt-water mucus and dilute it. By doing so, causes dehydration from the inside out of the slug and this eventually kills the slug.

Sprinkling salt on slugs may not be a pleasant option as it may seem cruel but many people use it to get rid of slugs. Some sprinkle salt around on the ground to repel slugs rather than sprinkling the salt directly on them.

Create a barrier

Another way to get rid of slugs is by creating a barrier. Naturally, these animals love to crawl everywhere but their soft sensitive body dislikes crawling over anything that could irritate their skin. This weakness can be used to your advantage especially in your garden by encircling your plants with barriers. These barriers will definitely make the slug turn around and change its direction.

You can sprinkle the following around your plants as barriers:

• Coffee grounds
• Wood ashes
• Sand
• Crushed eggshells

Also, copper wire or copper tape can be used as a barrier. One can place them around the garden beds or plants so that when the slug crawls across it, it gets an uncomfortable feeling like a small electrical shock. This will definitely keep the population of slugs in the house or garden in check.

Remove garden debris

Getting rid of your garden debris is an advisable way to keep the slug population in check. Slugs like to live in garden debris such as leaf litter or mulch and they lay their eggs in it. Therefore, to get rid of slugs in your garden or around your house it’s advisable to remove the debris around.

Using companion plants to increase the natural predators of slugs

There are some organisms that are natural predators of slugs such as snakes, beetles, toads, frogs, and other beneficial insects. Ground beetles, for instance, are a common predator of garden slugs, and to attract them and increase their population one can plant white clover around the house or in the garden. An increase in their population will definitely cause a decline in the population of ground beetle.

Removing Slugs manually

This is a natural way to get rid of slugs in the house or garden by just picking them off your plant or surface areas around your house. After removing them soak them in a bucket of soapy water to kill them or take them somewhere else far from the garden or home. It’s preferable to do the picking after dusk.

Planting Trap Crops

You can plant trap crops to get rid of slugs in the garden. The whole idea is to sacrifice some plants as bait for the slugs. Planting a crop that you know the slugs like will make them focus on such trap crops and avoid the other crops in the garden. Then, one can concentrate the manual slug removal method on those plants.

There are some plants that the slugs can’t resist even though they generally like tender leaves and shoots. Basil and marigold are examples of plants that these slugs love to eat. You can make a border of any of such plants to draw the attention of the slugs from the tender seedlings.

Beer Traps to get rid of Slugs

Another effective and common way to get rid of slugs in the garden is by using a beer trap. It is cheap and easy to make as well as effective. This is because slugs are attracted to the yeast’s scent in the beer. However, beer traps are not recommended as a first option to get rid of slugs because in as much as these traps drown and kill slugs it kills other beneficial insects as well. Hence, it is only recommended when there is an overwhelming infestation of the slugs.

In order to make a beer trap, get a clean shallow container and bury it in the ground with a small part of it sticking out of the ground. Then, fill the container with any kind of beer. The beer attracts slugs as they tend to like the yeasty smell of the beers. As they perceive the beer, they crawl into the container of beer and meet their demise. You may need to place these beer traps every 3 feet away for maximum effect which may be quite tedious and costly especially when dealing with a larger space.

Using Grapefruit Traps

Grapefruit traps as well as other citrus fruit traps have a less deadly effect on beneficial insects compared to beer traps. Get a grapefruit in order to make a grapefruit trap and scoop out the flesh inside. Then in your garden, place the empty grapefruit half upside down and leave it overnight. These slugs tend to be attracted to the sweet scent of the grapefruit and take cover in these citrus domes. In the morning, you can remove the grapefruit half that is likely to be filled with slugs and discard them far away from the garden.

Economic Importance of Slugs

In as much as slugs could be a nuisance in the garden causing damages to fruits and vegetables, they have some importance. In actuality, a small population of slugs is good for the garden as they break down garden debris thereby turning it into nitrogen-rich fertilizer which enhances the nutrient in the soil.

Another importance of slugs in the ecosystem is that they are a natural source of food for some organisms in the habitat. Predators of slugs are birds, frogs, toads, snakes, and many beneficial insects.

Snail vs slug

The snail and slug are part of the gastropods mollusk species, thus they may be similar but are not the same animal as some people think. Slugs and snails are very similar in their appearance, mating habits, diet, and habitat. However, their major difference is the presence or absence of a shell. The land snails have a shell on their back, which they retire into for protection. This shell is absent in slugs, even though some slug species have a very small shell or internal shell.

Let’s look at some of the similarities and differences between the snail and the slug.

Similarities between snail and slug

• The bodies of the snail and slugs are soft.
• They both leave a trail of slime and excrete mucus that prevents moisture loss and allows them to move along the ground.
• Dehydration is harmful to both the slug and snail because of their soft bodies.
• They both have tentacles with eyespots on the end.
• The snail and slug both have broad flat bottom muscular feet that are covered with epithelial cilia.
• They both move slowly.

Differences between slugs and snails

Frequently Asked Questions

Is a slug an insect?

Slugs are not insects and are totally different from insects. Slugs belong to the phylum Mollusca whereas, insects belong to the phylum Arthropoda. This means slugs are more closely related to octopuses and squids than insects.

Mollusca is one of the most diverse groups in the animal kingdom and includes a broad spectrum of soft-bodied creatures such as clams, octopi, and oysters. Slugs belong to the class Gastropoda which is the same class as snails and this class happens to be the largest group in the phylum Mollusca.

Are slugs dangerous?

Generally, slugs are not dangerous. The only disadvantages of these animals are the damage they cause to plants in the garden. They can eat vegetables and fruits and prefer tender leaves and seedlings. Hence, the slug feeding on all the leaves of the plant will eventually kill the plant.  They are nocturnal, so they hide during the day and feed at night.

It is fair to say that slugs are only dangerous to the plants around us and in the garden, and typically can’t harm humans. However, they can carry disease in that the slime on the slug skin can carry a parasite. So it is advisable to wash any part of your body that comes in contact with the slime. Wash your hands with water and soap after gardening.

Is slug a snail?

In as much as the slug may look like a snail, it is not a snail. The slug and snail belong to the same class Gastropoda but are not the same animal. Many people mistake the slug for a baby snail and this is a wrong conception.

Slugs are different from snails and you can tell by the presence or absence of a hard shell. Snails have a coiled large hard exterior shell for protection that they can retract into whereas, the slugs lack this hard exterior shell, though some slugs may have an internal shell or a reduced shell.

The majority of slugs evolved and came from snails that have an external shell that is made up of calcium and other minerals.  Over time, these slugs lost part or all of their shell. However, some slugs kept possession of a remnant shell beneath a soft outer mantle.

According to the hypothesis, it is stated that in damp temperate regions, unavailable calcium and a damp environment contributed to the gradual loss of the slug’s shell. A snail can retract into its shell when the weather is hot and dry in order to prevent desiccation. Whereas, a slug has to enter the soil or go under vegetation to prevent themselves from desiccation.

Are slugs poisonous?

Even though slugs may be slimy and cause damage to your plants, they aren’t poisonous to humans. Generally, mollusks such as slugs are harmless to handle, though they can carry parasites. These parasites can be transmitted to people through accidental ingestion of unwashed produce.

Slugs feed on vegetation and decaying plant matter and other organic matter such as animal feces. As a result of the slug’s icky diet, one needs to wash their hands after handling a harmless slug because one could ingest one of the parasites it might carry.

Some slugs pick up the parasite, Angiostrongylus cantonensis (rat lungworm) as they feed on rat feces. The rat lungworm can cause meningitis in humans. Moreso, as slugs vary in size, one is likely to miss the smaller ones among unwashed fruits, salad greens, or vegetables. Hence, it is advisable to wash all farm produce thoroughly and after handling any pet or wild slugs, one should endeavor to wash hands.

How many noses does a slug have?

Slugs don’t have a structure of a nose as we do. In humans, our nose functions as a breathing tube as well as a sensory organ to smell. For slugs, their anatomy is different, they do not per se have a nose. Rather, for gas exchange their single lung opens externally through an opening called the pneumostome. This opening is heavily vascularized to allow gas exchange.

In regard to the sense of smell, land slugs like other land gastropods have two pairs of tentacles on their head that are retractable. The lower pairs of tentacles called oral tentacles provides a sense of smell and are used to detect chemicals in the air whereas, the upper pair of tentacles called optical tentacles serves as a light sensor and at its ends are eyespots. Some people refer to the 2 pairs of tentacles that the slug has as the nose and that is very incorrect.