They are driving amateur gardeners crazy: certain slugs can devour entire vegetable beds, and even hanging containers are not safe. The situation is particularly bad at the moment, say experts.

It has been a hotly debated topic in hobby gardening forums for weeks: Plants that have been painstakingly grown are eaten down to the stump by slugs overnight. This year, it is said, there are an incredible number of them – an impression that experts confirm. “Yes, it is bad this year,” confirmed Michael Schrödl from the Zoological State Collection Munich (ZSM).

“After the drought years from 2018 to 2022, in which the populations collapsed accordingly, we now have the second very wet year in a row,” explained Markus Pfenninger from the Senckenberg Biodiversity and Climate Research Center in Frankfurt. The populations had already recovered last year and were able to start this year from an already high level. The mild winter certainly didn’t do any harm either – “but according to our observations, only extremely cold winters have a really lasting negative impact.”

If the lettuce disappears and glittering slime bands spread across the beds, it was probably the Spanish slug at work. The technical name is Arion vulgaris, also known as the large garden slug. It is found in many places – but only very sporadically in Spain, as researchers have discovered in recent years. Contrary to what was long assumed, it was probably not introduced from the Iberian Peninsula through fruit and vegetable imports after the Second World War – so the name is misleading.

In fact, the species has probably lived for a very long time, at least in southwest Germany. Since the 1960s, it has been appearing more and more north and east, often in high densities. To the chagrin of gardeners, these are real super snails: the brownish-reddish animals are excellent climbers, and raised beds are no problem for them, as Michael Schrödl once explained. Even a high-hanging container does not stop them: they rappel down on the slime thread. They can smell lettuce and vegetables from dozens of meters away.

Dry lawns and gravel paths may be a problem for other native slugs, but not for Arion vulgaris. According to experts, it reproduces faster, eats more and, if necessary, sits in the blazing sun to feed without being harmed. In addition, genetic analyses show that it mixes a lot with other species – and in this way possibly acquires new, favorable characteristics for the respective environment. And as if that were not enough: a fully grown Arion vulgaris – apart from Indian runner ducks – has hardly any predators of interest. Some ground beetles can also eat young slugs or their eggs.

Some hobby gardeners are currently stating in forums that they collect dozens or even hundreds of slugs every day. According to Pfenninger, part of the problem is probably that there are fewer and fewer animals that eat young slugs, such as hedgehogs and toads. “Arion vulgaris is profiting from the desertedness of gardens,” said Schrödl.

One measure against slugs is based on their preference for beer – the animals generally like the smell of fermented products, which indicates potential food: the beer trap. According to experts, however, the seductively smelling “drinking hall” attracts slugs from all over the area – only a small proportion of them drown, the rest start feeding in increasing numbers.

It is therefore recommended to only water in the morning, to surround beds with sand strips or snail fences and to regularly turn potential egg-laying sites such as boards lying on the ground out into the sun to dry them out. Or, for people who can do this: “A quick cut in the front third kills the snails immediately,” as Schrödl explained.

“Coffee grounds are said to help because caffeine is a neurotoxin for snails,” said Pfenninger. Collecting them is also considered a way to control the population – but the snails must not end up in the forest or elsewhere in nature where they threaten to displace native species. Urban dog parks, on the other hand, are a good place, according to Schrödl: “The droppings are eaten by the slugs.”

This is generally a factor that is quickly forgotten: Arion vulgaris may be very annoying, but it is also very useful in the garden because it removes droppings and carcasses and gets composting processes going.