by Whit Gibbons

October 12, 2008

Hurricanes spawn numerous environmental changes, including excessive rainfall. Almost no one today believes the once common myth that small frogs sometimes fall out of the sky during heavy rains. Nonetheless, an abundance of frogs and toads can be seen hopping around after heavy rains. An autumn with above average rain in some parts of the country has brought frogs to the attention of many people. The following are questions people have asked.

Q. I have seen several different sorts of frogs during recent rainy spells. How many kinds of frogs and toads are there in the world?

A. Scientists have described 5,645 distinct species of frogs throughout the world and 34 different families. The family of the true tree frogs has the most species, with more than 850 species described from the Americas, Europe, Southeast Asia, and Australia. Many are characterized by having expanded toe tips that aid in climbing and long, thin legs for jumping. A completely different family of frogs known as the Asian tree frogs, which occur in Africa, Asia, and Indonesia, has almost 300 species. Although they look and behave like the other tree frogs, they are not closely related.

The so-called true frogs make up another large family of frogs, with more than 830 described species. The most familiar ones have robust bodies and strong hind legs and include the well-known bullfrog, several kinds of leopard frogs, and rare gopher frogs of the Southeast.

The most common and largest family of toads throughout most of the globe is the family Bufonidae with more than 500 species. Members of the family are found on all warm continents except Australia, although since the introduction of the tropical American cane toad it is now established in many parts of that country as well. The species of toads differ among and within countries, but the squat brown insect-eaters commonly seen in gardens and backyards in most parts of the United States are also found in regions as diverse as Great Britain, China, India, and Argentina. The rare burrowing toad of southern Texas, which ranges through Mexico and Central America to Costa Rica, and the purple frog, a rare burrowing species from India, are distinctive in that they represent the only species in their family.

Q. I have lived in three southern states where we seem to have a lot of different kinds of frogs. Which states and which geographic regions of the world have the most species of frogs?

A. Of the more than 5,600 species of frogs known, 107 are found in the United States. Russia and Canada each have 24 species, compared to 27 in France, 226 in Australia, and 300 in China. All of these are low numbers compared to tropical regions of South America, where the highest numbers of frog species are found. For example, Ecuador has 444 species of frogs; Colombia has 678 species; Brazil has 776.

In the United States, the humid southeastern states from the Carolinas to Texas have the greatest concentrations of species. Alabama, Georgia, South Carolina, and North Carolina all have high numbers of native species, with 30 species each. Florida now has 32 species of frogs with the inclusion of three established introduced exotics in the Miami area. Texas has more species than any other state with 41, in part because of the presence of several predominately Mexican species along the border.

None of the large western states from New Mexico and Colorado to California and Oregon has as many species as any of the coastal southeastern states. No northern states have as many species of frogs as southern ones. For example, North Dakota has nine species, and Alaska has only five native species. Hawaii is the most depauperate of native frogs, having none. However, a half dozen species of introduced frogs now live in Hawaii, including species from Japan, Puerto Rico, the U.S. mainland, and tropical America.

Amphibian biologists have reasons for concern as many of the world's species are declining, and several have recently gone extinct. Learning more about these fascinating creatures is the first step in solving environmental problems they face.

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