Time capsule: Looking for a few good wood frogs

Time capsule: Looking for a few good wood frogs

Note: This article was originally published 30 years ago, on Aug. 7, 1996. Brian Barnes and author Ned Rozell have since retired from the University of Alaska Fairbanks, and scientists now know that the wood frog's internal body temperature can dip to 0.6 degrees below zero Fahrenheit while overwintering. So the wood frogs are still out there, hopping around and readying for the long winter ahead!

The office phone rang while Brian Barnes discussed with me his need for wood frogs. The caller's loudness forced Barnes, a University of Alaska Fairbanks associate professor of zoophysiology, to tilt the phone away from his ear.

"He's got some frogs," the voice boomed. "He don't wanna sell 'em. He wants to know what they eat."

The caller, a man from Fox, told Barnes that he and his son had read Barnes' unusual classified ad in the Fairbanks Daily News-Miner: "Wanted: Live wood frogs collected in or nearby Fairbanks. Needed for UAF study on wood frog overwintering biology. Where do they go? Will pay 25 cents for small; $1 each for large."

As father handed the phone over to son, Barnes lobbied with 8-year-old David, a student at Weller Elementary. If David sold Barnes his frogs, Barnes would tell David's class about the unique way the farthest-north amphibians survive the winter. David wouldn't budge.

"He wants to keep his frogs," Barnes said, smiling as he hung up.

Barnes needs wood frogs because he wants to find out more about how frogs can freeze in the fall and then hop around in spring as if they hadn't spent the last seven months as tiny green ice cubes. He'll use the frogs in a fall semester biology class where students will explore the ways northern critters survive the Alaska winter.

Wood frogs, which range from thumbnail- to palm-size, leap amid Alaska ponds and forests from Southeast to north of the Brooks Range. They catch our ears during springtime as they croak out choppy melodies from breeding ponds. In late July and August, the largest adults disappear, presumably into small nests of compacted forest litter. What happens next leads to a question Barnes hopes to answer along with his students: Just how cold can an Alaska wood frog get?

In wood frog studies performed in the Lower 48 and Canada, researchers found wood frogs survived until the temperature dropped below 20 degrees Fahrenheit. Barnes and other researchers found during a recent yellow jacket study that temperatures under the insulating snowpack of the Interior can drop to at least 5 degrees, so Alaska wood frogs must be doing something different than those Outside.

Wood frogs adapt to Alaska cold by becoming sweet, Barnes said. As the temperature drops below freezing, wood frogs' eyeballs and extremities begin to freeze. The creeping ice front apparently sends a message to their tiny livers, which start converting glycogen to sugary glucose. Glucose floods into vital cells, where it helps the cells resist drying, which can lead to frostbite in human flesh.

Wood frogs are freeze-tolerant, which means that water freezes when it's pushed outside cell walls. As winter progresses, a frog's eyeballs and brain become rock hard. Its heart stops beating. It seems as dead as a 40-below midwinter day, but it's not.

"When they thaw, their hearts start beating and off they go," Barnes said.

Barnes will recruit seven or eight big wood frogs and a couple hundred little ones for the study. He plans to glue tiny radio transmitters on the backs of the bigger frogs, then release them. Once they settle down for the winter, he and his students will track them to their dens and place temperature sensors on their bodies and in the surrounding forest litter.

Come springtime, the class should have a winter's worth of information on how cold the cold-blooded creatures got, and how much the snow and forest litter insulated the frogs from the frigid air. Further study of the glucose-laden blood of the overwintering wood frogs could even help medical researchers increase their understanding of how to control diabetes.

If you want to do your own wood frog research, Barnes recommends getting a permit from the Alaska Department of Fish and Game. He had to get one after learning it was illegal to possess any native wildlife in the state of Alaska, even the tiny wood frog.

Since the late 1970s, the University of Alaska Fairbanks' Geophysical Institute has provided the Alaska Science Forum column free in cooperation with the UAF research community. Ned Rozell retired in May 2026 after 31 years of writing this column.