Wandering Tigers and Zombie Frogs in the Garden
By R. Gary Raham
Mostly sunshine-filled blue skies seasoned with just a dash of water vapor lured me to Colorado when I was a newly certified science nerd. I have remained a happy resident even though the state can test its inhabitants with occasional torrential rains, blasts of arctic cold and extended periods of drought. I can compensate for the extremes with sump pumps, REI parkas and municipal plumbing services, but what about other animals that call our state home? Many creatures, with and without backbones, have found ways to dial down their metabolisms and wait for good times to return.
I met one such resident while scrambling to keep water from flooding my basement. While bailing out a window well, I was greeted by a paddling tiger salamander (Amblystoma tigrinum) that, as far as I could determine, had lain dormant in the dirt lining my window well ever since a previous rain storm had stranded him there.
During the winter one year, another salamandrian tiger turned up in a spadeful of dirt. (I can’t recall quite what lost treasure I was digging for, but I know my young daughter was involved.) The animal looked and felt like a misplaced rubber toy, but after a few minutes resting in the palm of my warm hand, the salamander began to twitch. We brought her inside where she revived and thrived for the rest of the cold season.
In winter, creatures capable of digging, like the tiger salamander and American toad (Bufo americanus), either burrow beneath the frost line—or often co-opt rodent burrows—to create snug dens called hibernacula.
The first tiger had resisted drought by estivating (sometimes spelled aestivating) while the second had successfully hibernated. (Aestas and hiberna is Latin for summer and winter, respectively.) A wide assortment of amphibians like salamanders and frogs, as well as mollusks such as snails and slugs and a few burrowing mammals, use one or both techniques to wait out cold or drought by either slowing metabolism or suspending it completely.
Estivating amphibians typically burrow into the ground and shed several layers of intact skin to form a protective, waterproof cocoon. Their metabolism slows, but doesn’t stop. Their nostrils remain exposed on the surface of the cocoon for breathing. When rains return, the animal sheds its shroud and digs back to the surface world.
In winter, creatures capable of digging like the tiger salamander and American toad (Bufo americanus) either burrow beneath the frost line—or often co-opt rodent burrows—to create snug dens called hibernacula. Their metabolisms slow until warmth returns. Aquatic frogs, dependent on oxygen rich water, may lie on the bottom of a pond or lake or only partially cover themselves with bottom mud. Some may slowly swim now and then; presumably to expose their skin—a critical breathing organ—to more dissolved oxygen in the water.
According to Rick Emmer, the lead keeper of The Rainforest at Cleveland Metroparks Zoo, wood frogs (Rana sylvatica) and the spring peeper (Hyla crucifer) seek out cracks in logs or rock formations or dig deep into leaf litter. They may even freeze such that their hearts stop beating—but they will revive when warmed. As Emmer observed, “there really is such a thing as the living dead.” The secret is antifreeze. While ice crystals form in some peripheral tissues, high concentrations of glucose in the heart and lungs save these hibernators from destruction. We can only assume that if the amphibians lose a few brain neurons in the process, they can get by without them.
Paleontologists have even discovered that burrowing is a time-tested way to survive nature’s crueler trials. Dave Varricchio found an odd egg-shaped fossil with a crooked sandstone “tail” in 95-million-year-old rocks in Montana. The tail turned out to be a fossilized burrow and within the oval-shaped lump of sandstone they discovered the remains of a shovel-snouted dinosaur about the size of a Labrador retriever along with the tiny bones of her young.
Even farther back in time, 300 million years ago, during the mega extinction that nearly destroyed all life on Earth, a hardy creature called Lystrosaurus—that paleontologist Anthony J. Martin describes as looking like “an unholy threesome between an iguana, a pig, and a naked mole rat—survived tough times by digging burrows. Martin tells all in his book, The Evolution Underground (Pegasus books, 2017).
Expect to find the tiger salamander almost anywhere in our state from lakes, glacial kettle ponds and beaver ponds in the mountains to cow manure-polluted puddles on the plains. Like me, this amphibian tiger calls Colorado home, but when things get a bit tough topside, you may turn her up below ground waiting for Colorado’s typically clear skies and mellow climate to return.
Gary Raham is a nature writer and illustrator. He is the author of: The Restless Earth: Fossils, The Dinosaurs’ Last Seashore, A Singular Prophecy, and other titles of science fact and science fiction.