(C) Jack Ballard
The sound of frogs chorusing from wetlands and the edges of ponds and lakes is a sure sign of summer. Across the eastern portion of our nation, from Florida to Maine, the zesty trills of spring peepers, a tiny, gregarious frog of vernal pools and marshes is a sure sound of spring. While the vocalizations of a spring peeper are melodic to the human ear, the sounds of other frogs are not. The croakings of bull frogs are loud and not particularly musical, no matter the season in which they occur.
Among the large category of amphibians known as frogs, differences in size, color, behavior and biology are as variable as their sounds. Spring peepers mature at around an inch in length and weigh just over one-tenth of an ounce. A bulky old bullfrog might reach eight inches in length and weigh over three pounds. Frogs’ color can range from dull olive or brown to the brilliant shades of green, blue, yellow and red adorning the bodies of tropical frogs. Even the eyes of frogs show a remarkable amount of variation, not only in color, but also in shape. The pupils of some frogs are round, similar to those of humans. Others have pupils shaped like horizontal ovals which enhance daylight vision. Vertical pupils, that narrow into slits during bright light but expand during twilight and darkness like those of a cat allow other frogs exceptional night vision.
While differentiating between frog species is a difficult task in itself, another biological riddle surrounds the creatures. What is the difference between a frog and a toad? Actually, the answer to this question is simple. All toads are frogs. Amphibians commonly known as toads and frogs all belong to the scientific order, Anura, which is derived from the Greek word for “tail-less” and refers to frogs. However, biologists do make a distinction between “true frogs” and “true toads.” In common usage, the term “frog” and “toad” differentiate creatures with divergent physical appearance and behavior within the Anura order, differences spawned by adaptations to various habitats.
In general, toads live in drier environments than water-loving frogs, although they do need water in which to lay their eggs. The skin of toads exhibits bumps and bulges, a characteristic responsible for the erroneous belief that handling these creatures can give humans warts. Frogs, by contrast, exhibit a smooth, often shiny or slimy appearing skin. Frogs and toads also differ in locomotion. Frogs hop, toads walk. Many frogs can hop an incredible 20 times their body length, a feat roughly equivalent to a human jumping over 100 feet. In a competition in South Africa, a frog was once recorded jumping over 33 feet. Tiny Australian rocket frogs can leap 50 times their body length. While frogs hop everywhere they go on their highly-developed hind legs, toads have short hind legs, better for walking than hopping.
Toads and frogs are also distinguished by other characteristics. Frogs have large, bulging eyes while the eyes of toads don’t appear to protrude from their heads. Excellent swimmers, frogs have webbed hind feet to aid their locomotion in water. The feet of toads often display more finger-like appendages, used by some species for digging in sand or loose soils. Finally, frogs lay their eggs in clusters while the eggs of toads are laid in long strings that look like a chain. However, between amphibians obviously bearing the appearance of a “frog” or a “toad” are many species of the Anura order exhibiting characteristics of both. It’s not unusual to discover a frog with warty-looking skin or a toad with a noticeably slimy look about it.
Whether frog or toad, the same basic lifestyle governs the reproduction and growth of these creatures. Both lay their eggs in or near water. In spite of the fact that a mother frog may lay hundreds of eggs, a very small percentage of them actually hatch into tadpoles, the next phase of development into a frog. Some eggs are infertile, others dry up in the sun, while a significant number of the spawn may also be eaten by predators.
Once an egg hatches, usually after about a week in the water, it becomes a tadpole. Initially, tadpoles are simple creatures consisting of primitive gills, a tail and a mouth. For about the first week, tadpoles are nourished by the yolk of their egg that remains in their gut. Then they began feeding on algae at the water’s surface as they gain locomotion.
Around a month into the life cycle of the tadpole, skin begins to form over its gill and it grows teeth. Now it is capable of eating dead insects and other foods. At six to nine weeks, the tadpole becomes more slender, forming legs and a noticeable head. Somewhere around nine weeks, tadpoles lose their “fishy” look and began to resemble frogs with a long tail. Within three months of hatching, the tadpole transforms to what looks like a frog with a tail, or a froglet. Soon afterward, the tail disappears and the creature’s metamorphosis from tadpole to frog (or toad) is complete. Depending on the elevation and severity of the climate, however, the process may take much longer.
From the spawn hatching in the puddles and marshes of the United States comes many unique and interesting species of frogs and toads. Leopard frogs of various species are all colored with trademark spots that give them their name. These frogs are highly sensitive to pollutants, making them an excellent indicator of water quality. Habitats where they should be abundant but are not are usually contaminated. In the northern part of the country, wood frogs survive the winter with a very unusual adaptation. They burrow into fallen leaves and plant matter on the forest floor to hibernate. When the ground freezes, an icy shell develops around the frog’s body, triggering a dramatic increase in blood glucose levels that essentially serves as antifreeze.
Pollutants and habitat destruction are detrimental to many species of frogs and toads, some of which are endangered. However, one of the greatest threats to many native species of frogs are other frogs. Bullfrogs, with their relatively massive size and voracious appetite prey on other frogs. Native to the eastern United States, bullfrogs have been transplanted to other parts of our country and to at least 15 other countries, often with devastating results. Bullfrogs brought to California in the late 19th century to feed miners have colonized much of the state and are directly or indirectly responsible for the extinction of some 100 species of other frogs. In Florida, Cuban tree frogs most likely entered the ecosystem as “stowaways” on cargo vessels. Now established in the wild, they prey on a half-dozen of native tree frogs, potentially driving them into extinction.
Fascinating creatures, frogs and toads also offer a notable lesson in biology. Plants and animals are best left alone. Individual species have adapted to particular environments through millenniums of natural selection. Humans are the best neighbors to unique frogs, toads and other wildlife when we avoid transplanting them to other places and protect the habitats in which they live.