Many visitors are surprised, but yes, we have poisonous snakes in Switzerland.
Meanwhile because of limitations in their habitats they are very rare, but still watch out for them if you sit on rocks or grab onto stones on the ground.
If you are biten, stay calm and see a doctor. The venom is not very dangerous, there was no deadly incident reported since the 1960's.
The Ticino is known for heavy rain and that causing floodings.
Be aware if locals or the authorities speak out warnings, it can be serious!