A Chinese jellyfish species known as Craspedacusta sowerbii has been living in Swiss lakes for more than 60 years. It was first recorded in Lake Geneva in 1962, and scientists believe it arrived through the trade of aquatic plants, possibly via the water hyacinth, a plant commonly used in ornamental water gardens. This jellyfish is unique because it spends most of its life in a microscopic, polyp form that is nearly invisible to the naked eye. It only transforms into a visible, floating jellyfish when water temperatures rise above about 25 degrees Celsius, a condition that typically occurs during the summer months. When it does become visible, the jellyfish is only around 2 centimeters in diameter and floats near the surface of the water. These visible stages last only about ten days, making it challenging for researchers to study the species. Despite its elusive nature, Craspedacusta sowerbii has been found in several Swiss lakes, including Annecy, Zurich, and Neuchâtel, as well as in Tête d'Or Park in Lyon. The presence of this jellyfish may indicate rising temperatures in freshwater environments, as its visible form appears only during the warmest periods of the year. This species is not unique to Switzerland. It has also been observed in other parts of the world, including the United States and Canada. Its global spread is believed to be linked to the trade of aquatic plants and animals, which can unintentionally transport small organisms across borders. The jellyfish's life cycle is tightly connected to water temperature, with its visible phase occurring only when the environment is sufficiently warm. Although Craspedacusta sowerbii is harmless to humans, its presence in new areas can provide valuable information about climate change and water temperature trends. Scientists continue to monitor its spread, using it as a biological indicator to understand how warming temperatures may affect freshwater ecosystems.