Biologists have known for a long time that frogs are very vulnerable to changes in their environment. Frogs across the globe were being found with deformities, such as extra legs, and species were going extinct. By the mid 1990s, it was still being speculated that the cause of the mutations was the weakened ozone layer, which was allowing too much ultraviolet radiation to filter onto the planet. Today, however, most scientists believe that the culprit is fertilizers leaking into the lakes and rivers where frogs live. The fertilizers cause certain types of snail species to thrive, and these snails often host parasites. The parasites, in turn, infect frogs when they are still in their tadpole stage. Cysts form on the tadpoles, which creates the mutations that are being observed.

Besides the malformations seen in frogs, there is another, even more troubling concern: many species of frogs—some estimate about 100 species are vulnerable—are threatened with extinction, and many others have already disappeared. In this case, the culprit is global warming. Because frogs have thin skin, they are vulnerable to environmental changes. Increased temperatures have caused fungi—some scientists specifically blame the chytrid fungus—to infect frog skin, and this leads to the lethal disease Batrachochythrium dendrobatidis (BD). The good news is that it is easy to treat and cure frogs; the bad news is that, even if they are treated, once released back into the wild they are likely to be reinfected. To help arrest the extinction rate, zoos around the world have been rescuing sample populations and breeding them in captivity.