Gray treefrogs
Hyla chrysoscelis and Hyla versicolor

There are two species of gray treefrogs in Ohio, and they are identical in appearance. They can be distinguished by measuring the size of their red blood cells, by the trill rate of their advertisement calls, and by other technical methods. In many respects they are very similar and will be treated so here. Important differences between the two species will be described where appropriate.

Fig. 18 Gray treefrog – gray color phase
Fig. 19 Gray treefrog – green color phase

The common gray treefrog (Hyla versicolor) is the species found in much of the northern two-thirds of the state. It is the gray treefrog in northeastern Ohio. Gray treefrogs are the largest treefrogs in Ohio, reaching lengths of 42-54 mm. Females average larger than their counterparts.

The gray treefrogs are the most remarkable species of frog or toad in Ohio at changing color. A frog may be any of many shades of gray (Fig. 18), green (Fig. 19), brown, or nearly black. Most gray treefrogs have an irregularly star-shaped blotch on the back, and a light spot beneath the eye is characteristic. The concealed surface of the thigh is bright yellow to orange with scattered dark ink spots. Yellow pigment extends down the leg and onto the toes of many individuals. Males develop dusky to nearly black throats during the breeding season.

Digital discs are large and very well developed; consequently these frogs are excellent climbers and commonly are heard calling from high in trees. They can even climb glass and are often observed on warm nights clinging to windows or house walls in pursuit of insects attracted by lights.

Gray treefrogs are seldom on the ground except during the breeding season. They breed in transient or permanent ponds located in swamps, forests, swimming pools, or in fields occasionally long distances from woodlots

Gray treefrogs emerge from hibernation in early to mid-April and are one of our last frogs to appear in the spring. Males call irregularly for days to several weeks from trees and shrubs in forests before moving toward breeding ponds. The extended breeding season begins in late April or early May and continues intermittently through late July or even early August. Eggs average 1.2 mm in diameter when laid but reach 4-6 mm when hydrated. They are laid in small floating masses of 10-40 that hatch in three to five days. Each female may lay as many a 1800 eggs.

Tadpole development is rapid in the warmer water of late spring and summer with transformation occurring in 45-65 days when the tadpoles have reached a length of 42-48 mm. The newly transformed young are green and lack the dark markings on the back found in adults. Two years are required to become sexually mature, and they may survive seven to nine years.

Their advertisement calls are given while on the ground or when in trees or shrubs. Calls of the two species are distinct when given by frogs at the same body temperature. Both species produce a trilled or pulsed call. Calls of the common gray treefrog generally have mellow sounds with low trill rates of less than 34 pulses per second (Fig. 20). Those of Cope's gray treefrog (Hyla chrysoscelis) tend to be harsh, less melodious, and have trill rates higher than 34 pulses per second (Fig. 21). The trill rate varies directly with temperature; as the temperature increases so does the trill rate. With some practice you can train your ear to detect the difference.

Gray treefrogs hibernate on land, and the common gray treefrog is known to produce glycerol, an antifreeze used by some insects to protect cells during the freezing process. Without this protectant the frogs would be forced to hibernate on or in the substrate of ponds or swamps or at least below frost line on land.

• Gray treefrogs have large digital discs on theirs fingers and toes.
• A diagnostic black-edged light spot below the eye is present in both species.
• An irregularly-shaped pattern on the back and flanks may be conspicuous, light in color, or absent.
• Check the concealed surface of the thigh and calf of the hind leg for a wash of bright yellow or orange.
• Gray treefrogs change color slowly and may be found in gray, green, olive, or many hues of those colors.