Slugs and snails have become invasive in most parts of the world:
- North America
- South America
These are the most important invasive species:
The black slug (Arion ater)
Its home is Europe and it has spread to Australia, Canada, and the United States.
The black slug can also appear in brown or white. Even green, yellow and multicolor are possible.
In Europe, the black slug lives in woods and is not considered a pest.
In other areas, however, the black slug has become a seedling predator; it is threatening ecosystems in Alaska and Canada.
The grove snail (Cepaea nemoralis)
A native of Europe, it has also spread to North America.
Fortunately, this snail is not normally interested in living plants and is therefore not a threat to horticulture or agriculture.
The garden snail (Cornu aspersum)
This species is also a native of, and common in, Europe.
There, the garden snail is even a predator of the eggs of invasive slugs and is not considered problematic.
Settlers brought it to America, Australia, New Zealand, and South Africa, where it became an agricultural pest.
In California, garden snails have become a pest, especially in citrus groves.
The leopard slug (Limax maximus)
Yet another species originally from Europe and North Africa that invades the whole world.
The leopard slug is present in:
- North and South America
- South Africa
- New Zealand.
In Europe, this slug is welcome because it is a natural enemy of the Spanish slug.
In other areas, leopard slugs are feared because they attack native slugs and snails and thereby threaten local ecosystems.
They are considered a pest neither in the garden nor in agriculture.
The vineyard snail (Cernuella virgata)
Originally, Mediterranean Europe, Western Europe, and Britain were home to the vineyard snail.
It has become invasive in Australia, where it is called ‘the common white snail’.
The Mediterranean snail
As the name suggests, this snail lives in the countries around the Mediterranean Sea.
It was introduced to many countries all over the world:
- North Europe
- South Africa
In most areas, it has become a serious problem and an agricultural pest.
In the USA, it is considered a potentially serious threat, and it has been suggested that the species be given top national quarantine significance.
The Spanish slug (Arion vulgaris)
For a long time, it was believed that the Spanish slug invaded Europe via salads from Spain, but this turned out to be incorrect.
Nowadays, it is believed that they spread with horticultural earth from France. As recent genetic studies have shown, these slugs are native to Central Europe.
In Spain, they did not exist; they migrated there only recently.
The Spanish slug is closely related to the common red and black slugs (Arion rufus and Arion ater) and shares the same natural enemies.
One of the reasons for the population boom of Arion vulgaris is that its enemies have mostly disappeared from gardens.
Find out here: How to promote the natural enemies of slugs and snails.