"Unlike its native relatives, the Spanish slug is highly active and mobile. This is believed to be one reason they are so invasive — they simply spread quickly, making them hard to control," Kruus said. That's why coordinated action between neighboring properties is essential to combat the species.

As for which methods to use, Kruus said there are no great success stories — neither in Estonia nor elsewhere in the world. There are only small victories. "No single method is a magic wand for eradicating them. You have to use a combination of approaches," she noted.

Beer, toxins and ducks

People struggling with the Spanish slug should start by sitting down and drawing up a realistic control plan, said Kruus. It's important to decide whether the aim is — unrealistically, in Kruus's view — to wipe out the invasive species entirely or to settle for protecting just certain areas of the property. "Start small and then move on to larger areas. That way, you'll also gain the experience needed to take on a bigger effort," she said.

When making a plan, Kruus advised considering how much time and money you can devote to it and whether it's worth pooling resources with neighbors. "You need to know your location. Is it drier or wetter? Is the vegetation lush or does it offer little shade?" she said. More overgrown areas provide habitat for natural predators like hedgehogs and adders, but also make slugs harder to spot than on a neatly mown lawn.

"If you have nearby areas from which it's likely there will be a constant invasion, you might think about installing a barrier," she suggested. For particularly heavy infestations, electric fencing is an option. Kruus noted that hardware stores sell a product called SnailStop, available in strips up to 30 meters long. "If you have a neighbor who just ignores the problem and lets them spread, I can't think of anything more effective right now," she added.

This year, she said, collecting slugs has been widely promoted as a fun community activity. "But considering that people usually come out in nice weather and slugs are active at night or in the rain, hand-picking is relatively inefficient," she explained. Slugs spend 60–70 percent of their time in hiding, so collection should be repeated multiple times and combined with mass-trapping methods.

A variety of attractants should be used, whether poison or traps, Kruus said. With beer traps, she advised choosing carefully: not all beer works the same. In a trial she conducted this year comparing three pilsner-type beers, the results varied greatly. "The most effective in my test was a Czech Pilsner, which luckily was one of the cheaper options," she recalled.

Foreign sources recommend partnering with a local pub and using beer drips collected from tap trays. The trap liquid doesn't have to be beer — it can be souring milk or any other fermenting liquid.

"For those who want to wage serious war in their garden, planting a few 'trap plants' is a good idea," she added. These can be sacrificial lettuces or other juicy treats for the slugs, which should then be checked daily for pests to collect.

In fair weather, when slugs prefer to stay hidden, they can be lured into artificial shelters such as slug mats sold in stores. "Any boards laid between garden beds or coverings like mats and rugs will also work," Kruus said. The slugs gather underneath, making them easier to remove.

The best-case scenario, according to Kruus, is to involve the slugs' natural predators, especially birds. Thrushes and starlings are known to peck for them on lawns. "I don't know if they eat the larger ones, but ducks certainly do — mallards, common teal and the right breeds of domestic ducks," she said. Hedgehogs, toads and even adders and grass snakes can also help.

"The more different methods you can implement within your protected area, the more effective your fight will likely be," Kruus said. But she cautioned that in rainy summers, all control measures tend to work less effectively. "In dry weather, slugs need more moisture to survive, so they're more likely to come to the traps," she said.

Persistence and drought the keys to victory

In some ways, the best time to fight the Spanish slug has already passed, said Eha Kruus. "The positive side is that the Spanish slug produces only one generation a year. So, for their numbers to get really high, it takes several years," she explained. Now, however, there are so many that in rainy weather they're visible everywhere. "They're out in the open now and the problem is no longer hidden," she said.

Looking at the year as a whole, Kruus recommends setting out the first traps in spring, when the weather warms up. It's not known whether the Spanish slug overwinters in Estonia as eggs or as juveniles. Most likely, she said, they do so as eggs. If they survive as juveniles, those could hide in sheltered spots and make it through the winter. "So traps should already be in place in the spring," Kruus noted.

She also urged people not to stop control efforts in dry years, as drought is an ally in this case. "Measures taken during drought are much more effective than in wet conditions. At that time, slugs have limited food and mobility and their reproduction is somewhat hindered," she explained.

The key, she said, is to know your battlefield — your own garden. "That's why we can't give one-size-fits-all recommendations — our landscapes are so diverse," she said. One neighbor may have one problem, another something completely different, because their yards are not alike. So a neighbor is not necessarily at fault if slugs are thriving in their garden.

"War is war and right now we have an enemy that doesn't fly, so it's still somewhere nearby," Kruus said. Sticking to a consistent "war plan" is essential. "If we're clever and persistent enough, we can at least reduce their numbers," she said.

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