Every year they drive vegetable garden owners to despair: some snails can eat entire vegetable beds, even hanging containers are not safe from them. In other bad news, sticky animals are definitely winning from climate change
If carefully grown lettuce disappears overnight and shiny ribbons of slime cover the beds, it’s probably at work: the Spanish slug. “It’s a real super snail,” says Michael Schrödl of the Munich State Zoological Collection (ZSM). Brownish-reddish animals climb beautifully. “Raised beds are not a problem for them.” And even a vessel hanging at a dizzying height does not stop them: “They descend on their own threads of slime.”
They are attracted to lettuce and vegetables, the smell of which they can smell at a distance of tens of meters. They also remember the places of delicious food. Simply tossing a Spanish snail into a neighbor’s garden often doesn’t do any good: “If there’s not something tasty in there, it’ll come back,” says snail expert Schrödl. “If you want to eliminate this snail by throwing it, you should practice long distance throwing beforehand.”
Two dozen nudibranch species in Germany
According to Schrödl, there are about 300 species of snails in Germany, about two dozen of which are slugs. “The taxonomy is still quite unclear.” In the case of snails with shells, their coloration and features often provide good taxonomic cues, whereas in the case of snails with variable shapes and colors, it is more difficult to clearly classify them as a species based on appearance. Genetic classifications aim to remedy the situation, but there aren’t enough data sets to do so yet, Schrödl explains.
The problem is also evident in the Spanish technical name slug Arion is ordinary, also known as the large slug. It leaves its slime trail in many places, but only very sporadically in Spain, as researchers have found out in recent years. Contrary to what has long been assumed, it was probably not imported with fruit and vegetables from the Iberian Peninsula after the Second World War – hence the misleading name. Rather, she has probably been living in southwestern Germany for a long time, at least according to Schrödl.
It is still not clear where this species came from, explains Heike Reise from the Senckenberg Museum of Natural History in Görlitz. The region of origin is probably somewhere between southwestern Europe – say, southwestern France – and the southwestern edge of central Europe, perhaps southwestern Switzerland or eastern France. But one thing is clear: since the 1960s, it has appeared more and more to the north and east, often with high density. The species causes damage and problems in Norway and Sweden, as well as in Poland.
“Almost every year there are new records for distribution in Northern and Eastern Europe,” says Schrödl. Transporting lettuce, vegetables and flowers, for example, played a role in the spread, Reise explains. It often first appears in places such as nurseries, cemeteries or garden waste storage, and then spreads from there.
Spanish slug “a real brute”
relatives like black (Arion ater) and red slug (Arion Rufus) such a triumphal procession failed. why “The Spanish slug is a real brute,” says Schrödl. Dry lawns and gravel paths can be a problem for other native slugs, but not for Arion vulgaris. He reproduces faster, eats more and, if necessary, sits under the burning sun to eat without harm. In addition, genetic analysis shows that it interbreeds strongly with other species – and thus it can acquire new favorable characteristics for the corresponding environment, says Reise.
In addition, the snail does not taste good. Schrödl tried all kinds of options with his colleagues, but even with a lot of garlic or marinating in broth, the animals remained above all one thing: “bitter.” Only Indian runner ducks are really crazy about Spanish slugs. Hedgehogs, thrushes, some beetles, shrews, toads – all classic snail hunters devour only the young of this species, the first enemy of adult specimens is only the gardener.
She often has to deal with tough molluscs: the Spanish slug is not the only one found in urban areas and gardens, and often in alarmingly large numbers. “The snail simply chooses the most comfortable option,” says Schradl. It is warmer in the cities than in the suburbs, and it is easier to survive the winter. In addition, it is the gardeners who provide the best living conditions: they water the greenery every evening and thus ensure a comfortable level of moisture. Animals that eat young snails, such as hedgehogs and frogs, are rarely found in areas without wild plants. “Arion vulgaris is a beneficiary of wasteland in gardens”.
In addition, many vegetables’ natural defenses against being eaten by pests have been bred to make them more palatable. This simply makes them more attractive not only to humans, but also to pests, Raise explains. “Bitter substances, for example, have an important function, they repel many animals, including snails.” Schrödl is also convinced: “This outbreeding definitely plays a role.”
However, in general, Spanish snails are not particularly picky, Reise explains. “They also like to try new things.” This can be fatal for the flora of the region newly inhabited by this species. According to Raize, many small seedlings were eaten during the project to relocate rare plant species to Upper Lusatia. In Sweden, the composition of grasses in the forest is changing. “If some plant species are severely depleted, it affects the entire ecosystem.”
Up to 50 animals are allowed per square meter
The problems are compounded by the fact that Arion is ordinary may occur in much higher densities than native species. “According to reports, 50 animals per square meter is possible,” Reise says.
There is still much research to be done on the impact on wildlife, Reise says. It is understood that snails eat small chicks of ground chicks, other defenseless or seriously ill animals and weakened peers. In addition, they crowd out related species – in the Herlitz area, the red slug interbred with Arion vulgaris in the years after Arion vulgaris appeared and eventually disappeared completely. Things look a little better with black slugs that live in forests – but here too there is a risk of complete displacement. Reise emphasizes that it is really bad to throw garden waste or snails collected in the garden into the forest.
Eventually, a new balance will be established in the habitats conquered by Arion vulgaris. It will not disappear anytime soon, especially in the face of climate change. “We can’t get rid of this snail, no way,” Reise said.
Gardeners often use appetite to destroy animal populations. For example, slugs like the smell of fermenting substances, which indicates potential food – this, Schrödl explains, is the basis of their preference for beer. Death in a beer trap is probably the most pleasant way to kill a snail – but this method of dealing with it is not recommended. The tempting smell of the “Trinkhalle” attracts snails from all over the area – but only a small part of them drown, the rest start eating in large quantities.
But how else to get rid of pests? Absolutely nothing prevents Shredl from sprinkling salt on animals. “It’s like pouring salt into an open wound.” In addition, salt does not kill safely and pollutes garden soil. Slug pellets are also not recommended. “There is always a risk that the wrong person will eat it.” Two active ingredients are approved: metaldehyde, which is dangerous to hedgehogs and other animals, as well as small children, and iron III phosphate, which is also used in organic farming. However, metaldehyde preparations work well only in dry conditions and, as with ferric phosphate III, do not have a particularly attractive taste for slugs.
Annoying, but also useful
Instead, it is recommended to water only in the morning, enclose beds with sand strips or snail fencing, and regularly turn over potential egg-laying sites, such as planks lying on the ground, in the sun to dry. Or for those who can: “A quick cut through the front third kills snails instantly.” You can also collect it, but where to put slimy creatures? “Under no circumstances should you go out into nature,” emphasizes Schrodl, a Munich expert. City dog parks, on the other hand, are a good place: “Snails eat poop.”
In general, despite all the worries about lettuce, one should not forget that snails are vultures in gardens: they remove excrement and carcasses, start composting and thus contribute to the health of the small ecosystem, as Schrodl says. “Arion is ordinary can be annoying in the garden, but it’s also extremely useful.”