In Denmark, butterflies of the oak processionary spinner species have established themselves and during the year caused authority decisions on closed schools and cleanup. On Monday evening, Lars Pettersson, assistant professor of zooecology at Lund University, was able to confirm that it had made it to Sweden when he was able to determine its species from an image in the report system Artportalen.
- It's a male. They spread more than the females do, and there won't be any eggs or larvae without females, so that particular butterfly means there is still no risk of it gaining a foothold in Sweden, says Lars Pettersson.
He says that several oak processionary spinners were sighted in Sweden in 2004 and further finds were made twelve years ago. All that have been seen and sexed have just been males.
Butterflies can generally fly far and every year one or two species enter Sweden, even ones that actually originate in southern Europe. Especially oak processionary spinners can certainly fly a few kilometers, according to Lars Pettersson, roughly as far as the width of the Öresund.
- If a female appears, they lay eggs on an oak tree. They then become larvae, but that would not be until this spring. The developed butterflies are not dangerous, but the larvae are.
It is the hairs on the larvae and old larval skins near the pupae that work protectively with an irritating substance containing the poison thaumetopoein. In case of human skin contact, it causes painful hives and shortness of breath.
- A wise thing is not to pet any hairy caterpillars at all, just to be safe, says Lars Pettersson.
Nils Carlsson, head of the species and nature unit in the Skåne County Administrative Board, has been flagging since early last summer that the oak processionary spinner will gain a foothold in Sweden. As the climate gets warmer, many species move north naturally, which means that by definition they cannot be considered invasive.
- In cases like this, there is no legislation and no task or the like for county administrative boards or the Swedish Agency for Agriculture. What happens anyway, which you can see clearly in Denmark, is that it suddenly becomes a big problem with demands that someone has to get a hold of it, says Nils Carlsson, who believes that Sweden is poorly prepared to handle the matter.
The oak processionary spinner gets its name because the larvae live in groups in oaks and when they have finished eating they seek out another oak in what looks like a procession. In southern Gotland, where the pine processionary spinner's sister species has existed for a long time, there are examples of campers who had a procession walk over them and who therefore had to seek care.
- I also know that there was a woman in Spain who saw a procession of oak processionary spinners on their way over a dirt road. She felt sorry for them and took them in her hands to move them to the other side, but then she had to seek treatment, says Lars Pettersson.
"Hell caterpillar", is that a fair nickname?
- They are not very common, neither here nor in Denmark, but it is clear that if you are affected by the hair, it is unpleasant. Many other things are also there without it stopping people from going to Gotland or Spain.
Will the oak procession spinner establish itself in Sweden?
- It's nothing strange if it does it - stopping a butterfly species that has spread feels quite hopeless. Then you can try to fight it like they do in Denmark if you think it's worth it, but there is a lot of coast and a lot of oaks here, says Lars Pettersson.
- On the other hand, there are many other species that eat oak in Sweden, which means that there is plenty of competition, so whether it will be successful remains to be seen. The oak processionary spinner also thrives further south, while our native species thrive better in colder climates.
