Herpetofauna is a term referring to reptiles and amphibians as one group. Often it is shortened to just ‘herps’. In Maine we have nine species of salamanders, nine species of frogs, seven species of turtles, and nine species of snakes. Lacking wings to migrate south, and unable to maintain their own body heat above that of ambient conditions (a trait that makes them ectotherms), most of Maine’s herps hibernate through the winter. Their techniques for doing so vary considerably.
Many Maine herps spend the winter burrowed into the mud in lakes and streams. These species include painted turtles, snapping turtles, musk turtles, and most species of frogs and salamanders found in Maine, excepting wood frogs, gray treefrogs, American toads, and spring peepers. The metabolism and organ function of most herps slows so drastically in the cold when they are hibernating that the oxygen absorbed through their skin from the water via diffusion is enough to keep them alive. Thus they can completely bury themselves in the mud of streams and ponds and survive, mostly inactive, all winter. Wood frogs, spring peepers, and gray treefrogs utilize a somewhat different strategy for winter survival.
Perhaps the most extreme method for surviving the winter is that of the gray treefrog. Treefrogs will often seek loose bark and
cavities of large trees to hibernate beneath. This means they are extremely susceptible to freezing and temperature fluctuations. To survive, gray treefrogs produce copious amounts of glucose in their organs. The glucose acts as an antifreeze, prohibiting bodily water from freezing solid. Instead, water in the body will freeze to the consistency of thick slush, allowing the organs to escape irreparable damage; a gray treefrog can tolerate up to 80 percent of its body freezing before incurring any negative effects. When the treefrog freezes, the organs cease functioning and the brain activity decreases dramatically. Incredibly, when the frog thaws, it can come out of hibernation functioning normally.
Some turtles, such as wood turtlesand Blanding’s turtles, are semi-terrestrial; they spend part of their time on land and part of their time in the water during the warmer months. As air and water temperatures cool signifying the upcoming winter these turtles head for running water (wood turtles) or deep swamps and ponds (Blanding’s turtles). They don’t hibernate in the mud of such waters like many herps, however. Instead they stay just below the ice and while their movements are significantly slower during the winter, they do remain active. The need for them to feed is significantly lowered due to their slow metabolic rates, influencing slow movement rates. However, like the amphibians, they are able to survive submergence all winter by pulling enough oxygen out of the water using the process of diffusion.
Box turtles burrow beneath leaf litter and brush piles or dig into loose soils to wait out the winter. They are capable of digging down to 19 inches into moderately packed to loose substrates to form their hibernacula, or burrow, where they will spend the winter. Turtles too close to the surface may be exposed to damaging freezing temperatures. Overwintering survival is likely a factor that limits the distribution of these turtles to southern Maine. Similar to tree frogs, peepers, and wood frogs, box turtles produce copious amounts of glucose to keep their organs from freezing solid. Up to 58 percent of their bodily water content can freeze to a thick slush consistency without any ill effects to the turtles.
With lakes freezing and snow falling, herps statewide are already settled in for the winter. Next time you are out ice fishing, cross-country skiing, or snowshoeing, take a moment to look at the ice you are on or the trees you are passing and consider the herps buried in the mud or partially frozen beneath the bark. You will realize Maine’s herps are truly incredible creatures.