Spring to Life: From Tadpole to Frog

It’s finally Spring, and in our part of the world, we’re ecstatic. We’ve had a rough winter—we had snow and ice on our city streets every day for about 40 days in a row! The crocuses are blooming in my backyard, and outside the city, frogs are springing to life.

In a way, Spring is a good time to think about our “inner amphibian.” After all, mammals are descended from animals that moved from aquatic environments onto the land over three million years ago. As embryos, our heads in the early stages of development look remarkably similar to shark embryos—with gill arches and all. The metamorphosis of frogs is a process that’s not all that different from what all vertebrates go through, but the difference is that most of the development of birds, reptiles, and mammals—such as the growth of the lungs and limbs—takes place inside an egg or inside the mother instead.*


A female frog first lays eggs underwater, sometimes hundreds of eggs, which form into a jelly-like clump called frogspawn, which floats on the water. Most of these eggs become food for other pond life, but some survive.

Tadpoles developing in eggs. © Dan L. Perlman/EcoLibrary.org

The tiny animal inside the egg grows for about a month, then hatches out of the egg. It looks like a small black fish and breathes underwater with feathery gills on each side of its head.

The tadpole’s tail begins to grow; it wiggles its tail to swim. Tadpoles are also called polliwogs. (The word “polliwog” is from Middle English polwygle. Pol means “head” and wiglen means to “to wiggle”). The tadpole eats algae and other plants that grow underwater.

Tadpole. Photo from Wikipedia.


After several weeks, tadpoles begin their metamorphosis. Two tiny bumps appear near the tadpole’s tail—these will grow into back legs.

Two more bumps appear near the frog’s head—these will grow into front legs. Lungs begin to grow inside the tadpole’s body and the feathery gills disappear so that the tadpole will be able to breathe air.

The tadpole now has legs for hopping and walking, lungs for breathing air, but its long tail is awkward on land. Until the tail shrinks and is absorbed into its body, the froglet stays in or near the water.

Froglet with tail. Photo courtesy of www.scienceprojectlab.com


When the tail is gone, the frog has completed its metamorphosis. The young frog will now feed on small insects, caught with their long, sticky tongues. It will eventually move away from the pond and find a safe place to grow.

This Spring, take some time to visit a nearby pond or swamp and see this process yourself. And check out the poster below that Susan designed for Earth Day, inspired by a photo by FROGS ARE GREEN photographer friend Joe Furman. All proceeds go to help our amphibian friends.

*I found this idea in Thomas Marent’s lovely and informative book, FROG.


Love Underground: The Shovel-Nosed Chamber Frog

We never stop being amazed by how amphibians are able to survive in the harshest environments. The Shovel-Nosed Chamber frog (Leptodactylus bufonius), for example, lives in the dry subtropical or tropical shrublands or grasslands of Paraguay, Argentina, Bolivia, and Brazil, in areas that have only intermittent freshwater lakes, marshes, and ponds. But this frog has evolved many incredible adaptations for overcoming the challenges of living in these mostly dry conditions.

Going Underground

Unlike most frogs, Shovel-Nosed frogs don’t have ponds or other aquatic areas in which to lay their eggs. They have only the muddy remains of ponds that have dried up. So with their shovel-like noses, they dig a chamber in the mud and then top it with a mud cone. Because no water can penetrate these chambers, the frogs produce a foam nest from the female’s albumin secretions to keep the tadpoles moist. But there is no food in the nest—scientists believe the tadpoles metabolize their own issues for food. Then the frogs wait for a big rainstorm that will wash away the burrow and create a predator-free pond (like a vernal pool) for the tadpoles to grow in. But the story isn’t quite over. After the Shovel-Nosed frogs vacate their burrow, a local toad reuses it as a hiding place.

Take a look at this amazing video of the Shovel-Nosed frog by FROGS ARE GREEN friend Joe Furman. We especially like the frogs’ little mating wiggle!

About the filmmaker:

Joe Furman lives in Houston Texas. He is a lifelong animal photographer and makes wildlife documentaries, mostly about reptiles and amphibians. He is also an artist and cartoonist and father of one.

Like most kids, Joe was attracted to frogs and toads and caught and kept them as pets for awhile, but then would release them back into the wild. He had, and still has, a neverending curiosity about tadpoles and the life cycle of frogs. In his twenties he got the chance to go to Costa Rica to look for the Golden Toads. This event set the course of his life ever since. He has traveled around the world with different organizations to study, film, and photograph reptiles and amphibians, and other wildlife. The kid has never left him. He still love frogs!