Slug - Top Facts & Information - Animal Corner (2024)

Slug, also known as land slug, is a common name used for any terrestrial gastropod mollusk that doesn’t have a shell, has just a small internal shell, or a very reduced shell. Slugs have soft bodies, which is actually just one big muscle in the stomach area that can be used for almost all of their body functions.

Slugs belong to the class Gastropoda, which also contains snails. There are different families of slugs and often these families are not closely related even though they look similar, which can make their taxonomy seem quite confusing.

Slugs are invertebrates and do not have any bones in their bodies. They can easily dry out, and for this reason they live in dark and damp habitats. There is no exact population count of slugs, but they are abundant across the world. They can be found on almost every continent.

Slug Characteristics

What a slug looks like can vary depending on the species. They are small to medium sized creatures with shell-less bodies and no bones. They basically look like a fat worm with two snail-like eyestalks! Their body is comprised of the tentacles, the mantle, the tail, the keel, the foot and the vestigial shell.

Like other pulmonate land gastropods, the majority of land slugs have two pairs of ‘feelers’ or tentacles on their head. The upper pair helps with light sensing and has eyespots at the ends, while the lower pair provides the sense of smell. Both pairs of tentacles are retractable. The mantle is positioned behind the head and is saddle-shaped. The part behind the mantle is known as the tail.

Some species of slug have a prominent ridge running over their back along the middle of the tail, which is called a keel. The bottom side of the slug is called the foot, which is what is used when the slug moves. Mucus is excreted from the foot, which helps to prevent damage to the foot tissues. The area around the foot is sometimes known as the foot fringe.

Most slugs are gray or light brown in color, but some are very brightly colored.

Slugs are hermaphrodites, which means that they have both male and female organs and can fertilize their own eggs. Most slugs retain a remnant of their shell, which is usually internalized. This is usually where calcium salts are stored.

While slugs do have a respiratory opening on one side of the mantle, they can absorb oxygen directly from the atmosphere. Their bodies are mostly made up of water and, without a full-sized shell, their soft tissues are prone to desiccation. Mucus helps to protect their bodies from dehydrating.

Slugs don’t have teeth or tongues. They have a special organ called a radula that has thousands of tiny protrusions that help them grind up their food.

Slug Lifespan

Depending on the species, a slug can live from anywhere between 1 and 6 years. However, their eggs can remain dormant for years and hatch when the conditions are right.

Slug Diet

Slugs are not picky eaters and most slugs are generalists and feed on a wide variety of organic materials. This can include leaves, flowers, fruit, dead plants, lichens, mushrooms and carrion. They often reside in vegetable gardens, and eat vegetables and herbs, as well as petunias, chrysanthemums, daisies, lobelia, lilies and daffodils.

Some slugs are predators and eat other slugs and snails, or earthworms. Some slugs are fungivores, fending on slime molds and mushrooms.

Slug Behavior

Slugs are mostly solitary animals, although on hot days will huddle together in the shade, flank to flank, to remain cool. They are mostly active just after rain because of the moist ground, and many species are nocturnal. They tend to spent their non active periods hiding in damp places such as under tree bark, fallen logs, rocks and man-made structures to help retain body moisture.

To move, slugs use their whole body. They contract a series of muscles on the underside of the body, which gives them the “wave” motion as they move.

Slugs are known to be aggressive with each other, particularly if they are competing for resources. This is usually more likely to happen in the summer, when there are less resources available for them.

Slug Mucus

Slugs produce two types of mucus: one is thin and watery, and the other thick and sticky. The thin mucus spreads from the foot’s centre to its edges, whereas the thick mucus spreads from front to back. The mucus secreted by the foot contains fibres that help prevent the slug from slipping down vertical surfaces.

The “slime trail” a slug leaves behind allows other slugs coming across the trail to recognize the slime trail as produced by one of the same species, which helps them to find a mate. The same slime trail can also be used by carnivorous slugs when hunting.

Slugs also produce thick mucus that coats their whole body, which keeps them moist but also can provide some protection against predators by making them difficult to pick up. This mucus can also be unpleasant to their prey to eat. Some slugs can also produce very sticky mucus which can incapacitate predators and can trap them within the secretion.

Some species of slug secrete slime cords to suspend a pair during copulation, too.

Slug Reproduction

Slugs are hermaphrodites which means they have male and female reproductive organs. For this reason, they don’t actually need to find a mate to reproduce, although most do.

Once a slug has located a mate, they encircle each other and sperm is exchanged through their protruded genitalia. A few days later, the slugs lay approximately thirty eggs in a hole in the ground, or under the cover of an object.

Slug eggs don’t have to hatch right away. They can remain dormant for years and hatch when the conditions are right.

Slug Location and Habitat

Slugs can be found all over the world. They prefer dark and damp habitats, because they have damp habitats and can dry out in warm habitats. It is for this reason that they are mostly seen in the spring and the fall.

Slugs can reside in areas created by humans like sheds and gardens, but can also live in areas such as woods and forests where there is less human activity. They like to live under rocks, stones, and rotten logs, and some even live underground.

Slugs and Humans

Slugs are commonly found in gardens and can wreak havoc. They can destroy the foliage of plants faster than the plant can grow, wiping out even very large plants in a short amount of time. They also eat fruit and vegetables, which can make crops more vulnerable to disease or difficult to sell for aesthetic reasons. Unfortunately, slugs can also carry dangerous parasites, which can cause harm to humans if touched.

Humans use a verity of methods to prevent slugs from causing damage to plants. These can include iron phosphate bates, crushed egg shells, coffee grounds and beer traps. Salt can also be used to kill slugs by causing water to leave their body.

Slug Importance

While to many people, especially gardeners, slugs can be a real nuisance because they eat vegetables and plants, they are actually very important to the ecosystem. This is because they also eat decaying plant material and fungi. Carnivorous slugs also eat dead specimens of their own kind.

Slug Conservation Status

The exact population of the slug is not known, but it is very unlikely that slugs are a threatened animal. They are widespread across their range, with, on average, 200 slugs living in 1 cubic m (35 cubic ft) of soil.

Slug Predators

Slugs are preyed on by vertebrates and invertebrates. The vertebrates include reptiles, such as snakes and lizards, birds, such as blackbirds, starlings, rooks and owls, fish, amphibians, and mammals such as foxes, badgers and hedgehogs. Invertebrates such as beetles are also known to prey on slugs.

To help prevent slugs from being preyed on, they contract their body and make themselves hardened, compact, and round when attacked. This allows them to attach themselves to the substrate beneath them.

Furthermore, the mucus they produce makes it difficult for predators to grasp them, and this mucus can even incapacitate their predators. Some slugs can self-amputate their tail to escape from predators

Slug FAQs

Are slugs poisonous?

Slugs are not poisonous to humans. In fact, some species of slug are even edible. However, they don’t taste great! The average slug you might fin din your garden will not hurt you, although they can host a dangerous parasite called rat lungworm. Slugs contract the parasite by eating infected rodents’ feces.

What is the difference between a snail and a slug?

The biggest difference between slugs and snails is the lack of shell in the slug. Slugs evolved from snails and lost their shell over time. The shell of snails is made of calcium and other minerals, and offers the snail a place to retract when the weather turns hot and dry to avoid desiccation. The slug, on the other hand, must retreat underground.

Does salt kill slugs?

Yes. Salt draws the water out of their skin by osmosis, and they can die within minutes of dehydration.

What do slugs eat in my garden?

Slugs eat a lot in the garden! They eat plant leaves, stems and roots, as well as flowers, vegetables and fruits. Fortunately, they can also eat plant debris and fungi, so they’re not all bad!

Slug Taxonomy

There are various taxonomic families of land slugs that form part of different evolutionary lineages, which often includes snails, and therefore various families of slugs are not closely related. Their taxonomy can seem quite confusing.

Slugs belong to the class Gastropoda, which is made up of snails and slugs. Slugs belong to the subclass Heterobranchia and the informal group Pulmonata. Within Pulmonata, there are six orders, two of which, Onchidiacea and Soleolifera, solely comprise slugs.

A third informal group, the Sigmurethra, belongs to the order Stylommatophora, and contains various clades of snails, semi-slugs (snails whose shells are too small for them to retract fully into) and slugs.

The break down of slug taxonomy in the order Stylommatophora can be seen below.

• Subinfraorder Orthurethra
• Superfamily Achatinelloidea
• Superfamily Cochlicopoidea
• Superfamily Partuloidea
• Superfamily Pupilloidea
• Subinfraorder Sigmurethra
• Superfamily Acavoidea
• Superfamily Achatinoidea
• Superfamily Aillyoidea
• Superfamily Arionoidea
• Superfamily Athoracophoroidea
• Family Athoracophoridae
• Superfamily Orthalicoidea
• Subfamily Bulimulinae
• Superfamily Camaenoidea
• Superfamily Clausilioidea
• Superfamily Dyakioidea
• Superfamily Gastrodontoidea
• Superfamily Helicoidea
• Superfamily Helixarionoidea
• Superfamily Limacoidea
• Superfamily Oleacinoidea
• Superfamily Orthalicoidea
• Superfamily Plectopylidoidea
• Superfamily Polygyroidea
• Superfamily Punctoidea
• Superfamily Rhytidoidea
• Family Rhytididae
• Superfamily Sagdidoidera
• Superfamily Staffordioidea
• Superfamily Streptaxoidea
• Superfamily Strophocheiloidea
• Superfamily Parmacelloidea
• Superfamily Zonitoidea
• Superfamily Quijotoidea
• Family Quijotidae

Slug Species

There are over 40,000 species of Gastropods. It would be impossible to list all species of slug here, but below are some of the most common slug species and their taxonomy. Some of these slugs have common names, while others are known by their scientific names.

Leopard slug

• Order: Stylommatophora
• Family: Limacidae
• Genus: Limax
• Species: Limax maximus

The leopard slug, also known as the great gray slug, is native to Europe, but has been accidentally introduced to many other parts of the world. It is now found across Western Europe, Eastern Europe, Asia, North America, South America and Oceania.

This slug is among the largest keeled slugs, measuring 10 to 20 cm (4 to 8 in) in length and is generally a light grayish or gray-brown with darker spots and blotches.

The leopard slug is widely distributed and is listed as Least Concern on the IUCN Red List.

Black slug

• Order: Stylommatophora
• Family: Arionidae
• Genus: Arion
• Species: Arion ater

The black slug, also known as black arion, European black slug, or large black slug is a terrestrial slug that is native to Europe but an invasive species in Australia, Canada (British Columbia, Newfoundland, Quebec), and the United States (Pacific Northwest).

Without a shell, this slug produces mucus to deter predators. It usually measures from 10 to 15 cm (3.9 to 5.9 in) in length and is generally deep black, with some adults being brown or even white. Like other terrestrial slugs, the black slug is a hermaphrodite, meaning it can find a mate or self-fertilize.

Black slugs are edible but are rarely consumed by humans because they taste horrible.

Yellow slug

• Superfamily: Limacoidea
• Family: Limacidae
• Genus: Limacus
• Species: Limacus flavus

The yellow slug, also known as the cellar slug or the tawny garden slug, is an air-breathing land slug found in Scotland, England, Wales and Ireland as well as most of southern and western Europe. It has a yellow body with grey mottling, and pale blue tentacles. When extended, its body length can be 7.5 to 10 cm (3.0 to 3.9 in) long.

Red slug

• Order: Stylommatophora
• Family: Arionidae
• Genus: Arion
• Species: Arion rufus

The red slug, also known as the large red slug, chocolate arion and European red slug is a roundback slug found in western Europe, including France, the Low Countries, Germany, western Poland, Switzerland and the southern parts of the British Isles.

As its common name suggests, its body color is often reddish, sometimes very vivid, but can also be orange, yellowish, brown and grayish. Some individuals may be black. It is one of the largest species in its genus, measuring up to 150 mm when extended.

Kerry slug

• Order: Stylommatophora
• Family: Arionidae
• Genus: Geomalacus
• Species: Geomalacus maculosus

The Kerry slug, also known as the Kerry spotted slug, is an air-breathing land slug found in Ireland, north-western Spain, and central-to-northern Portugal. It usually measures 7 to 8 cm (2.8 to 3.1 in) in length and is dark-grey or brown with yellowish spots.

The name Kerry in the common name for this slug is derived from County Kerry in the south-west of Ireland where the slugs that were used for the formal scientific description were collected. As a round-backed slug, it has no keel on its back, unlike the slugs in the families Limacidae and Milacidae.

The Kerry slug is protected by conservation laws in the three countries in which it occurs. It is currently listed as Least Concern on the IUCN Red List.

Field slug

• Order: Stylommatophora
• Family: Agriolimacidae
• Genus: Deroceras
• Species: Deroceras agreste

The field slug, also known as gray field slug, milky slug, and northern field slug, is an air-breathing land slug found in Asia and northern and central Europe. It measures up to 5 centimeters long and is pale brown and tan in color. It lives in moist grassy and marshy habitat types and feeds on dead and living plant material.

Worm slug

• Superfamily: Limacoidea
• Family: Boettgerillidae
• Genus: Boettgerilla
• Species: Boettgerilla pallens

The worm slug is an air-breathing land slug found in much of Europe, parts of North America and parts of South America. It is a very narrow and slender slug, almost worm-like and sharply keeled. It can measure up to 60 mm long and is pale greyish, sometimes with a bluish hue.

The worm slug inhabits a very wide range of habitats, including gardens, grassland, coniferous and deciduous woodland. It can live at altitudes of up to 1750 m.

Marsh slug

• Order: Stylommatophora
• Family: Agriolimacidae
• Genus: Deroceras
• Species: Deroceras laeve

The marsh slug is a terrestrial land slug found in Europe, Asia and North and South America. It usually measures around 15 to 25 mm long is brown to dark brown in color. Its shape is almost cylindrical and it has thin, colorless mucus.

This slug needs permanently wet habitats and is usually found in lowlands and very humid habitats, swamps, riversides and wetlands. It is the only land gastropod that goes deliberately into the water and can survive for days submerged. The marsh slug is quite agile and can crawl quickly.

Durham slug

• Order: Stylommatophora
• Family: Arionidae
• Genus: Arion
• Species: Arion flagellus

The Durham slug is a terrestrial land slug found in Great Britain and Ireland. It usually measures between 60 and 100 mm and is often greenish in color but can range from yellow to black. It has colorless mucous.

This slug usually resides in sisturbed habitats, wasteground, roadsides and gardens.

Pacific banana slug

• Order: Stylommatophora
• Family: Ariolimacidae
• Genus: Ariolimax
• Species: Ariolimax columbianus

The Pacific banana slug is found on the Pacific coast of North America. It is the second-largest species of terrestrial slug in the world, growing up to 25 centimeters (9.8 in) long. This slug is notable for its coloring, and is often bright yellow with black spots covering the tail. It can also be greenish, brown, tan, or white.

The Pacific banana slug is the only species of the genus Ariolimax that is found outside of California. They are found in moist and damp areas of the forest floor. This slug is listed as Least Concern on the IUCN Red List.

Carolina mantleslug

• Superfamily: Arionoidea
• Family: Philomycidae
• Genus: Philomycus
• Species: Philomycus carolinianus

The Carolina mantleslug is found throughout eastern North America from Ontario to Florida and west to eastern Texas. It resides in swamps along the Gulf and Atlantic coasts. It measures up to 10 cm (4 in) long and is tan to tan-grey mottled with flecks of slightly darker brown.

Toga mantleslug

• Superfamily: Arionoidea
• Family: Philomycidae
• Genus: Philomycus
• Species: Philomycus togatus

The Toga mantleslug is found from Maine to northeastern Alabama, and also has populations in southern Mississippi and Louisiana. It resides in upland hardwood forests, at altitudes of 1200 meters (4,000 feet). This slug is tan to tan-gray and usually mottled with small spots of darker brown. It usually measures 50 to 80 mm long.

Virginia mantleslug

• Superfamily: Arionoidea
• Family: Philomycidae
• Genus: Philomycus
• Species: Philomycus virginicus

The Virginia mantleslug is found from north-central Virginia to Tennessee and west to eastern Kentucky, in upland hardwood forests on mountains above about 700 meters (2,300 feet). It is between 50 and 100 mm in length and the mantle is tan to tan-gray and usually mottled with small spots of darker brown.

Brownbanded arion

• Order: Stylommatophora
• Family: Arionidae
• Genus: Arion
• Species: Arion circ*mscriptus

The brownbanded arion is an air-breathing land slug found across most of Europe, except for more southern regions, and is also widespread in North America. It resides in broadleaved woods in temperate climates.

This slug usually reaches a length of 40 mm and is dark gray in color. Its mucus is colorless, or sometimes pale yellow.

Spanish slug

• Order: Stylommatophora
• Family: Arionidae
• Genus: Arion
• Species: Arion vulgaris

The Spanish slug is an air-breathing land slug found across much of Europe and is also found in North America. It resides on river and lake margins, forest edges and forests in valleys or meadows. It is a roundback slug and ranges in size from 60 to 140 mm. Its color ranges from yellow to black, but is most commonly brick-red, dirty orange, or brown.

Valencia slug

• Superfamily: Limacoidea
• Family: Limacidae
• Genus: Ambigolimax
• Species: Ambigolimax valentianus

The Valencia slug, also known as the cellar slug, the yellow slug, or the tawny garden slug, is found in Scotland, England, Wales and Ireland as well as most of southern and western Europe. It is also found China. This slug commonly resides in human habitation, and is usually found in damp areas such as cellars, kitchens, and gardens or under stones.

The Valencia slug can measure between 7.5 and 10 cm (3.0 and 3.9 in) and it has a yellow body with gray mottling, and pale blue tentacles.

Tree slug

• Superfamily: Limacoidea
• Family: Limacidae
• Genus: Lehmannia
• Species: Lehmannia marginata

The tree slug is an air-breathing land slug found in Spain, Norway, Ireland, Great Britain, Czech Republic, Netherlands, Slovakia, Poland and Ukraine. It mostly resides in woodland. The tree slug is a species of keeled slug that rarely exceeds 12 cm in body length. Its body is fairly long and narrow and is nearly transparent.

Winding mantleslug

• Order: Stylommatophora
• Family: Philomycidae
• Genus: Philomycus
• Species: Philomycus flexuolaris

The winding mantleslug is found from Quebec to northeastern Georgia, in upland hardwood forests up to about 1,500 meters (5,000 feet) in altitude. It hot weatehr, it can be found on logs, snags, or tree trunks well above the ground.

This slug usually measures between 50 and 100 mm and is tan to gray and usually mottled with large spots of darker brown. It produces a pale yellow defense mucous when irritated.

Dusky arion

• Order: Stylommatophora
• Family: Arionidae
• Genus: Arion
• Species: Arion subfuscus

The dusky arion is widespread throughout Central, North and East Europe and can also be found in China. It lives under fallen logs and under bark in woodland areas, but it also lives in hedges, gardens, pastures and dunes.

This slug is a roundback slug measuring between 50 and 70 mm. It is brown in color, ranging from black-brown through olive-brown to orange and bright reddish-orange.

Tandonia budapestensis

• Order: Stylommatophora
• Family: Milacidae
• Genus: Tandonia
• Species: Tandonia budapestensis

Tandonia budapestensis is an air-breathing, keeled, land slug that is native to Europe but is also found in New Zealand and North America. It measures up to 70 mm in length and has a yellowish-gray to brown or dark gray body, with numerous black spots.

This slug mainly lives in secondary man-made habitats such as farmland, but can also live parks, gardens and ruins. It requires humidity and buries and buries itself into heavy soils. It is a pest in crops of root vegetables for this reason.

Tandonia budapestensis is listed as Least Concern on the IUCN Red List.

Strubellia paradoxa

• Order: Acochlidiidae
• Family: Strubellia
• Genus: Strubellia
• Species: Strubellia paradoxa

Strubellia paradoxa is a species of freshwater slug and one of only two described species in the genus Strubellia. It is found in Indonesia and is reddish-brown in color, ranging from 5 to 40 mm in length. It lives under rocks in streams and creeks on volcanic islands.

Strubellia species are unusual among slugs in being sequential hermaphrodites, they become mature as males and later turn into females after copulation.