Timm pointed out that citizen science tends to operate on a so-called campaign logic. When something new and exciting happens, people report it more frequently. "The appearance of the Spanish slug was a hot topic in the past, and all enthusiasts wanted to document their observations. However, if the topic is not continuously discussed, interest wanes over time and new data no longer comes in," the specialist observed.

Timm also noted that people's interest declines when there are no summaries of the sightings or feedback. "The problem with various applications tends to be that if there are no leaders to keep the topic alive, it eventually falls by the wayside," he admitted.

However, according to him, the decrease in sightings cannot be attributed solely to a lack of enthusiasm. "The prolonged dry weather in the spring and early summer reduced slug movement, as it takes a lot of slime for them to travel from one place to another. Thus, they were harder to spot. Now that it's raining more, they will come out again, and the number of sightings will increase," Timm remarked.

According to Timm, July is when people see the Spanish slugs the most because many individuals reach their full size then. "Those that wintered in eggs are still growing. Smaller individuals are not as noticeable, but in July, most of them reach adulthood," the zoologist explained.

Despite their origins, Estonian winters do not harm the Spanish slugs much, Timm noted. "Unfortunately, we can't say that winter has dealt with them. There was a lot of snow during the cold weather. If it were -20 degrees Celsius on bare ground, we could hope that the adults wintering near the surface would perish. However, the eggs are reportedly able to withstand even temperatures as low as minus 100 degrees," he pointed out.

Invasion gearing up

According to Timm, years ago there was a belief in Estonia that the Spanish slug would probably not spread beyond gardens. Unfortunately, such hopes have now been dashed. "For example, if you go to Paljassaare or the zoo in Veskimets in wet weather, you can see them there. The Spanish slug is spreading throughout Estonia, including rural areas, primarily through gardens," the expert stated.

The main vector for slug spread, according to Timm, is plant material bought from nurseries, whether flowers or trees. "Often, slug eggs come with the soil. Unfortunately, there are still people who try to dispose of garden waste in nature, thinking it will decompose and cause no harm," he noted.

"However, it is precisely by dumping garden waste in nature that various other alien species, such as Japanese knotweed, bluebells and even snowdrops and lilies of the valley, spread. These are not native to our region but can thrive here," Uudo Timm concluded.

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