In 2013, scientists discovered that the African clawed frog—a species found all over the world—is carrying a deadly amphibian disease and is thus threatening hundreds of species of frogs and salamanders. Initially, the frogs were shipped around the world for use in human pregnancy tests from the 1930s to 1950s; if a female frog began ovulating within about ten hours after being injected with a woman’s urine, the woman was probably pregnant. Because other methods were developed to determine if a woman is pregnant, the frogs were released into the wild and are now spreading a fungus called Batrachochytrium dendrobatidis (Bd). Most of the surviving African clawed frogs have found a way to survive the fungus, but other amphibians are not as lucky. The disease infects the skin, causing it to thicken to around forty times more than normal—toppling the creature’s electrolyte balance and literally causing a heart attack.

The caecilians are mostly legless, wormlike amphibians found everywhere around the world, but mostly in tropical regions. Many are eyeless, have smooth skins, and burrow into the ground like earthworms. Not much is known about this group, and they are the least studied of the living amphibians. But it is thought their ancestors may have played an important part in the development of early amphibians.