The invasive leaf flatworm has already been found in Skåne, says Henrik Lange, coordinator for invasive species at the Swedish Environmental Protection Agency.
It doesn't like extreme cold, but the problem is that it can always hide. It crawls into the soil and if there is frost on the surface, it crawls a little further down.
But it is clear that if there were hard frost in November and minus 15 for several weeks, then most would probably die.
Snail in hibernation
The killer slug sleeps through the cold winter and is ready to pounce on the flower beds when the heat arrives.
The impact of a severe winter is marginal on that species, says Ted von Proschwitz, snail and slug expert at the Gothenburg Museum of Natural History.
In years when it has been relatively warm already in January–February, it has been seen that killer slugs have woken up from their hibernation far too early.
But they have since died if there has been a cold snap, because they are unable to go down a second time.
It's worse for the killer slug if it's dry in the spring, especially in May. But a wet spring means it's going to be a real slug year.
Survive everything
Ticks are not deterred by the winter cold either. Murielle Ålund, a researcher at the Swedish Veterinary Institute (SVA), says that they have received reports all winter, although not in large numbers, of dogs and cats that have come in with ticks.
In the north, if there isn't much snow and it gets really cold, some of them might die when they don't have the protection of the snow. But otherwise, they are pretty good at surviving anything.
Just like the killer slug, ticks are worse off if it gets hot and dry. At least our common ticks and the taiga ticks.
At the same time, we have had problems when it has been very dry, that we instead get other ticks that come from outside and that prefer warm, dry conditions.
