In a medical laboratory in France decades ago, a nurse would collect a small amount of a patient’s urine and inject it into an aquarium containing a live frog. If the frog laid eggs the next day, it indicated the patient was pregnant. This method, known as the Hogben test, was used from the 1920s until the 1970s. The frog used was the smooth clawed frog, Xenopus laevis, originally from South Africa. These frogs were imported in large numbers for pregnancy testing, but when modern tests replaced the method, many were released into the wild in western France without proper study or oversight. The smooth clawed frog has since established itself in rivers in the French departments of Maine-et-Loire and Deux-Sèvres, where it has thrived for over 70 years. However, it is now classified as an invasive species, meaning it is not native to the area and has caused ecological harm. The frog acts as a super-predator, preying on local amphibians, and it can spread a deadly fungal disease called chytridiomycosis, which has devastated native frog populations. The use of Xenopus laevis for pregnancy testing began in the 1920s when British biologist Lancelot Hogben discovered that the frog reacts to human hormones. Specifically, if the hCG hormone—associated with pregnancy—is present in a woman’s urine, the female frog will lay eggs within 12 to 24 hours. This test became widely used in the United Kingdom and later in the United States, where large colonies of the frogs were raised for diagnostic purposes. The release of these frogs into the wild was largely uncontrolled and occurred when the concept of invasive species was not yet a major concern for scientists. Adapted to the warm waters of sub-Saharan Africa, the frogs have shown remarkable resilience and have successfully colonized French waterways. Today, the smooth clawed frog is officially classified as an invasive species in France and is recognized as a vector for chytridiomycosis, a disease that has severely impacted local amphibian populations. European regulations now prohibit the import, breeding, transportation, and intentional release of the species within the European Union, except for those already kept as pets. Although trapping campaigns are ongoing in affected regions, completely removing the frogs from the ecosystem remains a significant challenge.