Like tiny amphibious chameleons, gray tree frogs (Hyla versicolor) change color to match their surroundings. Sometimes bark-like gray or brown, at times a leafy green, and at others a mottled combination of color that mimics lichens or rocks, these tiny frogs elude predators through camouflage. Sometimes they even display a shade of creamy white or tan. No matter what color they exhibit, all gray tree frogs have bright yellow or orange marks under their thighs.
Why are they “tree” frogs rather than just frogs? All species known as tree frogs (or treefrogs) have large toe pads that enable them to climb trees, sides of buildings, and other structures. Climbing trees is all about catching the wide variety of food available there on warm summer nights: small insects and their larvae, spiders, mites, aphids, snails and even smaller frogs. At night gray tree frogs also climb sides of houses to perch on windows and capture small moths and other insects attracted to light. Because gray tree frogs are nocturnal, I often hear rather than see them unless they perch on the windows. What preys on them? Small mammals such as skunks, raccoons and opossums. Snakes, birds and larger frogs also eat them.
Gray tree frogs typically inhabit woodland edges and gardens near water. We’ve seen them at our cabin in rural Minnesota, and my sister, who lives in a Twin Cities suburb, has regulars that hang out in her garden. They pop up in damp places — the cat’s water dish, inside her garden watering can, under flower pots, on the patio furniture and in her small fountain. Adults are typically found higher up in trees or shrubs, while younger tree frogs are more terrestrial.
Unlike most frogs, the gray tree frog sounds more like a bird as it trills its one-note call. They breed from April to July and call most frequently during May and June, though it can be as early as April and as late as September. Females lay their eggs near a shallow pond or pool of water. Hatching and development takes about 7-8 weeks. They reach adulthood in two years and the average life span ranges from 5 to 7 years. Adult size is generally 1-to-2 inches (3-to-5 cm) in length.
Tree frogs hibernate on land, usually buried under leaf litter, fallen logs and other materials. Their bodies produce glycerol, which is converted to glucose. Large amounts of glucose in the frog’s vital organs acts as an antifreeze. Ice crystals will form in the body cavity and under the skin, but the lungs and heart are protected from freezing, and stop functioning until spring. Warm weather will thaw the frog and it will revive and continue its life. Gray tree frogs live in eastern North America from New Brunswick to Manitoba, south to northern Florida and west to central Texas.