Leopard slugs: Introduce them into the garden?

Leopard slugs (Limax maximus) are often regarded as pests.

In Europe, this is a misconception because these slugs belong to the extremely useful inhabitants in the garden.

In the parts of America, Australia, Asia, and Africa, leopard slugs are an invasive species and could be harmful to the environment.

But normally the harm they do is little and their benefits predominate.

What is a leopard slug?

Leopard slugs are also called great gray slugs, tiger slug or giant garden slugs. The slug belongs to the family of keeled slugs.

Compared to other slugs, keeled slugs are slimmer and more elongated.

leopard slug great gray slug long

Leopard slugs owe their name to the leopard-like patterning on their body.

The animals probably originate from Southern Europe and have migrated to Central Europe over time.

In addition, they have been carried by humans to large parts of the world: North and South America, South Africa, Australia, Asia etc.


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Appearance

Leopard slugs reach a length of up to 8 inch (ca. 20 cm).

Their basic color ranges from light yellow to light gray or light brown.

The characteristic spots can be seen all over the body, which often have an elongated shape on the hindquarters. This visually resembles the grain of a leopard.

The number of spots varies greatly. There are also specimens that are almost monochrome.

Leopard slug great grey slug

Possible colors of a leopard slug show a great variety – as seen in the above picture.

Part of their frontal body consists of the so-called mantle shield with a rounded end.

In the mantle shield itself, there is a small calcareous shell with a length of up to 1/2 inch (13 mm).

This platelet is a remnant of the former snail shell and serves as protection for internal organs. The mantle shield can be lifted if necessary.

The soles of leopard slugs are mostly cream-colored.

On the right side of the body, in the rear part of the mantle shield, there is the breathing hole with an often dark border.

The rear third of the slug is formed by a narrowing back part. At the end of it, they can eject a defensive mucus when threatened or attacked.

In addition, leopard slugs – like almost all snails – secrete a colorless, tough mucus on which they move around.


Video: Leopard Slug close-up


What do the young slugs look like?

Young slugs hatch out of their eggs after about one month. They are still very small, and their appearance does not yet show a leopard pattern.

After hatching, they are glassy, light brown to white. The typical black spots and bands only appear with time.


Video: Leopard Slug Babies hatch from the egg | 4-week time-lapse


Where to find the great gray slug?

Leopard slugs can be found in parks and gardens, as well as in forests. Occasionally, they can also be found in the cellar if it is damp enough.

The animals are nocturnal and prefer places that are both shady and cool during the day.

They can bury themselves under plants or lie under stones and wood.

In this way, they protect themselves from predators. Typical places of retreat are piles of stones and dead wood, planters, or composters.

Generally, the slugs are loyal to their habitat. They usually move within a radius of 15-30 ft (5–10 meters) around their roost. They also form colonies over time.


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Natural predators

The natural predators of the leopard slug include insects, birds, amphibians, and mammals:

  • Ground beetles
  • Fireflies
  • Fowls
  • Songbirds
  • Ducks (e.g., runner ducks)
  • Frogs
  • Toads
  • Newts
  • Salamanders
  • Hedgehogs
  • Moles.

Video: Ground beetle attacks leopard slug


What does a leopard slug eat?

Leopard slugs are very useful animals and are therefore particularly popular in the garden. This is because the adult animals are themselves diligent snail hunters.

The slugs also eat slugs of the same size—sometimes even conspecifics.

However, they not only eat snails and slugs, but also the snail eggs.

This is why they help to prevent snail infestations in the garden. On the other hand, this is the reason they can do harm as an invasive species.

Leopard slugs are also among the natural enemies of the Spanish slug (Arion Vulgaris—Capuchin slug), as can be seen in the following video.


Video: Leopard slug eats Spanish slug


They further feed on carrion, fungi, lichen, animal excrement and dead plants. Thus, like almost all snails, they serve as a clean-up service in nature.

They eat and digest organic waste and fertilize the soil with their excreta. This work benefits all plants in the garden.

Sporadically, they can also feed on vegetables such as cucumbers, lettuce, or strawberries. However, they normally leave young plants in peace when foraging for food.

It is important for the animals to have a high-protein content in their diet. This is the only way they can develop and reach sexual maturity.

In a completely tidy garden, the animals usually find too little food.

Through their natural feeding behavior, the slugs will be able to contain a snail infestation over time and ensure a healthy balance in the garden.


Video: Leopard slug chases brown slug


What can be done to attract leopard slugs?

For great gray slugs to feel comfortable, they need shelter during the day that is both shady and moist.

Therefore, it is a good idea to pile up wood or stones all over the garden. These piles serve as shelters where the animals can hide.

If you cover them with brushwood and old leaves, you can also create a comfortable climate.

Disposing of leaves and brushwood in the garden is a bad habit that not only harms the leopard slugs, but many beneficial animals.

Old organic material should therefore be kept in the garden and left to rot in suitable places.

leopard slug in the garden

If you want to attract the leopard slugs from the neighborhood, you can, for example, create natural corners at the edge of the property where the animals can settle.

If there are no leopard slugs in the neighborhood, you can try to look for them in nature. Rainy days or the early hours of the morning when the ground is still covered with dew are suitable for this.

You can also buy leopard slugs in some pet shops or order them from breeders via the Internet (e.g., Collective Creatures).


Please be aware, slug pellets should not be used, as they are poisonous for all slug and snail species—as well as for pets and children.

leopard poisoned with slug pellets
This leopard slug was poisoned with slug pellets.

Leopard slugs themselves are not poisonous animals.

However, one should avoid touching them, as this triggers an increased stress reaction in their bodies.

Reproduction

Under suitable living conditions, the animals reproduce continuously.

Their sexual maturity begins at about 1.5 years. On average, slugs live for about 2.5 to 3 years.

Keeled slugs, like all snails, are hermaphrodites—males and females at the same time.

Eggs

Leopard slugs usually lay eggs twice in their lifetime. The number of eggs is between 100 and 300.

The eggs are distributed over several clutches. They have a diameter of about 5 mm.

Leopard slug eggs are transparent, cream-colored and not white like those of the Spanish slug.


Video: Leopard slugs laying their eggs


It takes about 3–4 weeks for the baby slugs to hatch.

Mating

The mating of two leopard slugs is a special spectacle that can be observed from June to September. They often choose a rotten tree as their mating site.

Before the sexual act, the slugs begin to circle each other and lick the end of their backs. This foreplay sometimes takes many hours. This leads to an increased production of slime.

To perform the final act, the animals let themselves hang down on a thread of phlegm. They wrap themselves tightly around each other and an impressive union of the sexual organs takes place.

Once the act is complete, one slug drops and the other pulls itself back up on the thread, eating it in the process.


Video: Leopard slug mating


Breeding

Breeding leopard slugs is recommended, especially in the months of August and September. During this time, the animals lay their eggs in light-protected places.

Once they have settled in a place, they do not leave it again. They then reproduce from year to year if they find enough food.

Over time, a natural balance is established. Their presence in the garden, as they themselves serve as food, also attracts all kinds of natural enemies of slugs and snails.

tiger slug leopard slug

Conclusion

In the UK, leopard slugs do not belong to the category of pests, but are beneficial organisms.

As a hunting slug / predatory slug, they help to create an ecological balance and prevent slug infestations.

It is therefore worth creating natural corners in the garden where slugs can hide and reproduce undisturbed.

Here are some tips on how to create an insect-friendly garden in which leopard slugs also feel at home.

In areas where they are invasive, it is important not to use slug pellets to kill them.

This would do more harm to the environment than the slugs do.


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Last update: January 17, 2023


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