First success in the resettlement of the edentulous gastropod molluscs

"We have found animals on around a quarter of the trees on which we released the toothless slugs (Balea perversa)," says snail expert Jörg Rüetschi, who is delighted with this initial success. Just over a year ago, he and employees of the Zurich Wilderness Park Foundation released a few hundred of the snails, which are only a few millimetres in size, into the Sihlwald. The mini snails previously lived on chestnut trees in Langenberg, which had to be felled. The snails' new home is on the ridge between Hochwacht and Schnabelburg. This move was financed by the nature conservation department of Grün Stadt Zürich.

Rüetschi has only found a few of the slender, spindle-shaped small snails on each of the trees, but still considers the result to be clearly positive. On the one hand, he has already witnessed snail relocations where no animals were found a year later. "On the other hand, it is quite possible that other animals are still living at the new location in Sihlwald," adds Rüetschi. Because the summer was very hot, the mini snails have retreated deep into the rough bark. This means that the still small young animals in particular are barely visible. "We'll know more in a year's time, the young snails will be slightly larger and therefore more visible," says Rüetschi hopefully. According to Rüetschi, we will have to wait patiently to see whether the resettlement is successful in the long term: "It will only be possible to say definitively after a few years whether a population can be maintained."

Attractive living conditions in the Sihlwald

The toothless slug feels at home on all trees with rough, torn bark, where it can withdraw into small hiding places. Beech trees, for example, have smooth bark for a long time, but very old trees of this species have deep cracks. So far, experts have not found any animals on beech trees. However, due to the suitable conditions, it can be assumed that Balea perversa would settle on old beech trees. Beech trees characterize the Sihlwald, which is on its way to becoming a natural forest and is therefore increasingly dominated by old trees. "In the Sihlwald, the toothless slugs will therefore find attractive living conditions in the long term," explains Isabelle Roth, Head of Natural Forest and Deputy Managing Director of the Zurich Wilderness Park Foundation. "Micro-habitats such as crevices in the bark or rotten areas of very old trees play an important role in the cycle of a natural forest. They provide shelter and food for many small and sometimes rare creatures," emphasizes the natural forest expert.

Moving to an already familiar place

The area around the Schnabelburg ruins in the Sihlwald is a well-known location for the edentulous snail. As the population has declined sharply due to a renovation of the ruins in summer 2011, the Zurich Wilderness Park Foundation hopes that the relocation of the mini snails from Langenberg will help the population to recover in the long term.

Further information

Bianca Guggenheim
Communications, Zurich Wilderness Park Foundation
Tel. 044 722 55 22
bianca.guggenheim@wildnispark.ch