Is it illegal to own a single hamster in Switzerland?

Illegal; it is considered animal cruelty to keep a social hamster species alone.

Owning a single hamster in Switzerland is illegal if the species is naturally social, such as the Roborovski hamster. Under strict animal welfare laws, social animals must have contact with others of their own species to prevent isolation and distress. While Syrian hamsters are naturally solitary and must live alone, keeping a dwarf variety in isolation can result in investigations by animal protection authorities. The law treats pets as sentient beings with specific social requirements rather than mere property.