<human>:  How many species of frogs are there in the world?
<bot>: There are over 5,000 species of frogs in the world, and that number is growing. Frogs are amphibians, and there are two main groups of frogs: the tree frogs and the froglets. Tree frogs have external gills and a tail, while froglets have internal gills and no tails. The most common frog in the world is the bullfrog.