Where have all the frogs gone?

Frogs play an important role in wetland ecosystems, but where do they go during winter?

Wood frog. Photo credit: Doug Wechsler, naturepl.com
Wood frog. Photo credit: Doug Wechsler, naturepl.com

Winter has crept – well, maybe slammed this year – across Michigan, covering most of the open water with ice and creating a glittering world without frogs. As a member of the amphibian class, frogs are dependent upon water for survival. So, where do all the frogs go in winter when their ponds are covered with ice? Like many other aquatic-based creatures, frogs have “migrated,” but they haven’t moved south like the water birds; they have dug in. Digging in or moving deeper into unfrozen mud is called vertical migration. Frogs in our neighborhood ponds across Michigan have dug into the soft mud at the bottom of their ponds.

Many people know that water is needed by all living things. Water is the primary component of most organisms and makes up about 75 percent of a frog’s body weight. But water in the winter can kill those that are unprepared. When water freezes, its molecules move apart. If this happens inside an organism, the cell membranes, which normally hold each cell together, stretch until the cell membranes break open and the cells are destroyed. If enough cells are destroyed, the organism will not survive.

Most cold-blooded animals, but specifically amphibians (frogs, toads and salamanders) and reptiles (snakes, lizards, turtles, alligators and crocodiles) burrow deep into the soil or mud then go dormant so they don’t freeze. By slowing their body functions, they can save enough energy so they don’t need to eat all winter long.

One exception is a type of tree frog that replaces most of the water in its cells with sugar as winter approaches. Because sugar does not expand as it freezes, this enables the tree frog to freeze solid. When spring arrives, it slowly thaws and converts its sugar back to water then hops away looking for food. Most of the rest of the cold-blooded animals slowly ramp up their metabolism in response to “spring” stimuli and reverse their downward fall migration to upward spring migration. Michigan is home to a wide variety of plants and animals depending on water for survival, yet needing various adaptations to survive water in winter.

You can help youth learn more about frogs and wetland ecosystems through participation in the citizen science FrogWatch program or delve into the secret lives of frogs and toads on the Michigan State University Extension website. For more ways to share science with youth in your life, please explore the MSU Extension Science and Technology webpage.

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