Frogs and toads have special traits | ECOVIEWS

Q. Last year, you provided facts about salamanders. What can you tell us about frogs and toads? How are they different from other animals? What makes them special?

A. Salamanders, although abundant in the Southeast, are amphibians with which few people have firsthand knowledge. But almost everyone is familiar with frogs and toads. The 54 families and 7,566 species of frogs and toads have many overlapping biological characteristics. Herpetologists lump the two together as a single group known as “anurans.” They have certain notable traits that set them apart in the animal kingdom.

1. In general, anurans differ from most other terrestrial vertebrates (mammals, birds, reptiles, salamanders) in that the young’s diet differs dramatically from the adult’s. Frogs and toads in the U.S. have some of the most eclectic diets imaginable. All adults are carnivorous, whereas tadpoles — the larval aquatic stage of development — are generally herbivorous. Tadpoles commonly eat algae or other plant material, although a few species eat small aquatic invertebrates.

2. Adult anurans lack a tail. Frogs and toads are readily distinguishable from other vertebrates in having long tails in the larval stage but no tail as adults. Some biologists might argue that the tailless great apes, including chimpanzees, gorillas and humans, have a tail during early embryonic stages, but these hardly qualify as having larvae.

3. Like many salamanders that begin their life as eggs and larvae in the water, most North American frogs and toads spend their adult life on land, making them some of the best biological indicators of an ecosystem’s overall well-being. A healthy population of frogs around a wetland is usually evidence that both the aquatic and terrestrial habitats are free from damaging pesticides or other contaminants.

4. Most adult anurans eat insects and other invertebrates, but some, such as the South American horned frogs, consume rodents, reptiles and other frogs. The common American bullfrog vies for the record of most diverse diet. Based on numerous documented records, bullfrogs eat insects, small mammals, birds, snakes and other frogs. I know personally of a case in which a large captive bullfrog consumed a baby alligator that was placed in its aquarium. Some spadefoot toad tadpoles in the Southwest have taken carnivory to the extreme: they cannibalize their own species.

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5. Perhaps the most impressive phenomena found among the anurans are the amazing variety of reproductive strategies in some tropical species. Exceptions rule the day. For example, after mating, the male of a Chilean and Argentinian species known as Darwin’s frog swallows the developing eggs that the female has laid on the ground and carries them around in his vocal sac for more than a month. One of nature’s more astonishing spectacles is froglets hopping from the open mouth of a male Darwin’s frog. Some frogs do other weird things reproductively, such as carrying their developing babies on their back. Certain tropical frogs lay their eggs on leaves suspended above water. Upon hatching, the young fall into the water below as tadpoles. Some tropical American frogs lay single eggs in water collected at the base of leaves of living plants and return repeatedly to deposit unfertilized eggs as food for the developing tadpoles. Frogs indeed have some singular behaviors.

6. Frogs span an enormous size range from big to little. The largest, the goliath frog of Cameroon in west-central Africa, can weigh up to 8 pounds and with its legs outstretched is about 2 feet long. At the other end of the spectrum, adults of pipsqueaks, the littlest frogs, are perhaps the world’s smallest vertebrates. Discovered in New Guinea, they are so tiny that three adults can sit end-to-end on a quarter!

Like all wildlife, frogs and toads have intrinsic value merely by virtue of existing. In addition they serve as sentinels, signaling that natural habitats are intact and unpolluted. Some of the winter breeding frogs have already begun calling. Listen for them on warm, rainy days and nights.

Whit Gibbons is professor of zoology and senior biologist at the University of Georgia’s Savannah River Ecology Laboratory. If you have an environmental question or comment, email ecoviews@gmail.com.

This article originally appeared on The Tuscaloosa News: Frogs and toads have special traits | ECOVIEWS