Out in the Woods

Caption: A baby gray tree frog

Photo: Kevin McKeon

The Versatile Bodies of Frogs

By Kevin McKeon, Maine Master Naturalist

Frogs were hopping around on Earth over 217 million years ago, scampering amid the other dinosaurs’ feet. Their long evolutionary trek has imparted these amphibians with many habitat-specific adaptations. Let’s begin with their impressive flair for breathing.

Almost all frogs emerge from their underwater eggs as tadpoles, breathing through gills and the vascular-rich skin of their tails. As these larval frogs grow, their tails shrink and lungs develop, allowing them to journey onto land.

Frogs get oxygen through skin and gills in water, and through lungs, skin, and mouth on land. While in water, adult frogs breathe dissolved oxygen passing through their skin and into their blood vessels, called cutaneous respiration. On land, their lungs suck in air by opening and closing their mouths, creating a vacuum called buccal pumping; oxygen is also gathered on land by cutaneous respiration. And yet another method for oxygen intake is through the lining of their mouths, much like their skin.

Now, for drinking; They do that through their skin, too, when in water. And some frogs that spend most of their time on land have a “seat patch,” a specialized skin surface located near their hind legs that they press on wet areas, allowing water to enter via cutaneous respiration.

Frogs’ big eyes give them nearly 360 degrees of vision and allow them to see underwater and in low-lighted areas. Also, since frogs do not chew their food, their specialized teeth grasp their food – and their eyes retract into their heads, pushing the food down their throats.

Hearing? Some frogs do some of that with their lungs! When the lungs are inflated, their inner body walls vibrate with the sound waves, sending sounds to inner ears to mix with sounds entering through exterior ears. This has the added effect of dampening some relatively unimportant sounds, like insects and other frog species, which allows them to better hear what’s important to them – the calls of their own species.

Wood frogs and spring peepers, among other frogs, have an amazing tolerance to winter’s cold, surviving in an almost totally frozen state in the leaf litter below the snow. Their livers release sugars that act as an antifreeze within the frog’s cells to prevent the cells from freezing and bursting. So, during early spring cleanup chores, if you uncover a seemingly lifeless frog while raking leaves, consider gently placing it in some out-of-the-way spot and covering it with a bit of leaves. You’ll be rewarded with the peeping or quacking of these early spring singers, and fewer insect pests! Listen to some of our singing frogs here.

Editor’s note: Did you see something unusual last time you were out in the woods? Were you puzzled or surprised by something you saw? Ask our “Out in the Woods” columnist Kevin McKeon. He’ll be happy to investigate and try to answer your questions. Email him directly at: kpm@metrocast.net