One hot summer day, my son and I discovered a tiny frog on the trail at a state park. We were in the forest, far from a creek or pond, and the little frog hopped along unconcernedly, peering back at us through its black mask. At home, I looked up the tiny amphibian and was delighted to learn that I had encountered a wood frog!
Over the next few years I started looking for wood frog eggs and tadpoles in vernal pools. We even tried raising some in the classroom! When I was looking for topics for chronological order texts, I decided to research the life cycle of the wood frog. These little frogs have fascinated students in my class for many years.
I enjoy teaching with this text so much that I have made it available in multiple formats. For a digital activity, click here: Informational Text: The Life of the Wood Frog.
You can also find this activity in a printable format, with other chronological order texts, here: Close Reading with Chronological Order Texts.
Reading level: 4/5, lexile 970
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The Life of the Wood Frog
Winter Nights
Think about spending the night in the forest on the coldest night of the winter. To survive, you would need to wear a heavy coat, boots, a hat, and gloves. Even with all of these items, it would still be a very cold, very long night.
In the forest, you might be sitting within a few inches of a tiny forest survivor. The wood frog lives through winter without a coat, without a hat, even without being warm-blooded. More amazingly, wood frogs have been found to freeze solid in winter. A night that would be dismal for you would be no big deal to a frozen frog-sicle.
Although they are small, wood frogs are interesting. From their birth in vernal pools to their secretive lives in upland forests, wood frogs have been surprising scientists for over a hundred years.
Springtime Awakenings
As the winter days grow longer and the temperature warms, the frozen wood frogs thaw out and awaken. Depending on the daily temperatures, this can happen in late February to early March. The wood frogs then head off to a special place called a vernal pool. A vernal pool is a forest pond that is only wet in the springtime. Because of this, no fish live in vernal pools.
Male and female wood frogs gather at vernal pools. Male wood frogs chorus at night, making sounds that have been compared to the quacking of a duck. Their chorus can be quite loud, often blending in with the sounds of spring peepers and other springtime frogs.
Shortly after mating, the female frogs lay eggs. They often create large masses of eggs, attached to a stick or some other vegetation. These large egg masses are called “rafts”. Putting many eggs close together may help keep the eggs warm. After only one or two short weeks at the vernal pool, the adult frogs leave to return to their solitary lives in the forest.
Growing up in a vernal pool
The wood frog eggs are left behind in the vernal pool. With no fish around, the eggs have few predators. But there is a risk to this strategy. The wood frog eggs need to develop into tadpoles quickly, before the pool dries up at the end of the summer.
Wood frog tadpoles emerge from their eggs in April. They are tiny, black, and hungry. In the vernal pool, they find plenty of food to eat—decaying leaves, algae, and other plant matter. As they eat and grow, the tadpoles change color, becoming more of a greenish-brown.
The tadpoles eat their way through the rest of the spring. Scientists have found that they are able to recognize their “siblings”, other tadpoles from the same wood frog parents. These siblings often group themselves together in the vernal pool. Scientists think that sticking together helps them to find food and avoid predators.
As May turns to June, the tadpoles start to grow legs. First, the back legs grow. Then, the front legs develop. Tadpoles stop eating shortly before they finish their transformation. Finally, their lungs develop and they are ready for life on land.
Warm weather can speed up the transformation process. As temperatures warm up, the tadpoles may develop more quickly. Tadpoles that have not developed when the vernal pool dries up may die or be eaten by birds or small mammals. For this reason, the faster transformation may help wood frogs to survive.
Return to the forest
After they have fully developed, the baby wood frogs leave the vernal pool. Unlike other frogs, wood frogs prefer dry, upland forests, and do not live near water as adults. Once the wood frogs leave the pond, they lead somewhat mysterious lives. If you go into the forest to find wood frogs, you may be disappointed. There is no one place where you can dependably find the small amphibians. But a small wood frog might jump across your path when you least expect it.
Wood frogs eat insects and other small invertebrates throughout the summer. When the air turns cold in November or December, they shelter under leaves or logs. Special substances in their blood actually promote freezing. By controlling the freezing process, wood frogs can prevent jagged ice crystals from tearing apart their cells. Instead, the ice forms in the spaces between cells. This allows the wood frog to survive being frozen.
This amazing ability of wood frogs was very surprising to scientists. The first accounts of frozen wood frogs, written in the early 1900s, were viewed with disbelief. In recent years, scientists have become very interested in this ability of wood frogs. Many biologists have investigated wood frogs too see if their freezing tolerance could be useful to humans, especially for medical procedures such as organ transplants.
Throughout the rest of the winter, even on those frozen nights when you would huddle indoors, wood frogs stay frozen in their winter shelters. In February and March, as the days grow longer and the temperatures increase, wood frogs awaken. Once more they make their journeys to the vernal pools.
by Emily Kissner
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