On a recent windy evening, I was weeding and mulching around the trees that line our driveway. What I thought was a leaf kept moving ahead of me until I finally figured out it was moving because it was alive! It was a small frog, and I was lucky enough to catch it on camera before it moved to a hideaway that was quieter and safer. My photo helped me identify this tiny frog as the wood frog, with its conspicuous dark mask extending from the eye through the eardrum to the shoulder, giving it a look of the Lone Ranger.
The wood frog’s scientific name is Lithobates sylvaticus. The genus Lithobates is Greek. Litho means stone, and bates means “one that walks or hunts.” The species sylvaticus is Latin and means “amidst the trees.” Both the common and scientific names tell us that the wood frog is a terrestrial frog, preferring moist woodlands (rather than ponds like the more common American bullfrog and northern green frog). It lives from northern Georgia all the way to the tundra of Labrador and Alaska, farther north than any other North American amphibian.
The wood frog is 1.5 to 3.25 inches long, generally tan, pink, or dark brown in color with some dark mottling on a white belly. It has distinct ridges along its back called dorsolateral folds. Its diet consists of a variety of terrestrial insects and other small invertebrates such as spiders, beetles, moth larvae, slugs and snails. It also consumes algae, decaying plant and animal matter, and eggs or larvae of other amphibians. In turn, the wood frog is food for larger frogs, a variety of snakes, herons, raccoons, skunks and minks. Its tadpoles are preyed upon by diving beetles, water bugs, leeches, newts, and aquatic insects.
Amphibians include frogs, toads and salamanders, and are cold blooded animals with a soft, glandular, often moist skin which is capable of absorbing oxygen into the body. They do not drink water but rather absorb water through their skin. Most frogs survive the winter by hibernating deep under water in our local ponds, lakes and streams. While they are cold and dormant, their body temperature doesn’t fall below freezing. The wood frog has a unique adaptation to winter; it nestles down into the leaf litter in the woods, spending the winter frozen!
The National Park Service’s (NPS) “Gates of the Arctic” gives a detailed description of the process. When winter comes, the wood frog’s abdominal cavity fills with ice and encases the internal organs. Ice crystals form between layers of skin and muscle, and the eyes turn white because the lenses freeze. Concurrently, the frog’s liver produces large amounts of glucose that flushes into every body cell. This glucose prevents the cells from freezing and binds the water molecules inside the cells to prevent dehydration. A winter hibernating wood frog has no muscle movement, no heartbeat, no breathing. When the temperatures warm, the frog thaws from the inside outward with the heartbeat starting first, followed by brain activity, and then the legs move. To view some frozen wood frogs, visit www.sciencefriday.com/segments/the-frogs-and-insects-that-freeze/.
The wood frog’s amazing winter endurance is of interest to researchers. How does the frog’s body withstand blood sugar levels 100 times higher than normal without damage, unlike humans who suffer when their blood sugar is only two to 10 times higher? Can the frog’s ability to freeze and thaw every winter and spring translate into improvements in human organ transplants? How does the frog stop and start blood circulation without blood clots or other injuries?
Even though the wood frog has a wide distribution in North America, they are elusive. Maybe you will get a sighting when you are doing your outdoor chores. The opportunity to see one up close and snapping a photo made the drudgery of weeding and mulching almost enjoyable for me!
Visit the Delaware Soil and Water Conservation District’s website at www.soilandwater.co.delaware.oh.us and follow us on Facebook and Instagram. Mark your calendar for the 2019 drive it yourself Farm Tour on Saturday, July 20.
Bonnie Dailey is deputy director of the Delaware Soil & Water Conservation District. For information, go to www.delawareswcd.org.