Green Tree Frog — Part 2

Hyla cinerea Daudin

The Green Tree Frog is most interesting when kept in captivity. It lives high among the ferns and vines of its moss-garden, and is especially fond of flies. It will see a fly at a distance of three or four feet, and will catch it, making but one leap over the intervening distance. It is said that this tree frog can leap a distance of eight to ten feet. When the call is given, the throatpouch is inflated and the body over the lungs swells and relaxes forcibly.

These tree frogs live at the margins of bodies of water, on the broad-leaved aquatic plants. They are abundant in southern gardens also.(Bay St. Louis, Miss. C. S. Brimley.) They are commonly seen resting on wellhouse or fence, or on the leaves of the okra or other plants of the garden.

In southern Illinois, Hyla cinerea is said to be found likewise on lily-pads and other aquatic vegetation at the edges of lakes, as well as in gardens and corn-fields.(H. Garman Bulletin Illinois State Lab. Nat. Hist., 1892.) The chorus as heard in Illinois is described as follows: "Its note resembles the tone of a cow-bell heard at a distance. Where abundant about water, the frogs are very noisy just before dusk, the chorus being broken, however, by longer or shorter intervals of silence. A single note is first heard, and, as if that were a signal, it is taken up and repeated by a dozen noisy throats till the air is resonant with sound. After a time it ceases as suddenly as it began, to be again resumed after a period of quiet."

The type specimens of Hyla evittata Miller were found in 1898 at Four Mile Run, Virginia. Before that date, the species, when found, had been supposed identical with the well-known Hyla cinerea. The resemblance of the two tree frogs is remarkable. The distinction can always be made without difficulty, however, since Hyla evittata lacks the outlining bands of white and has a thicker and less pointed head. Moreover, the skin of Hyla evittata is smoother than that of Hyla cinerea and has the appearance of being even smoother than it is, because this tree frog always has a shining, wet-looking surface. This characteristic of the skin makes the frog look as though it were moulded from smooth green wax. Again Hyla evittata has a marked tendency to display blue-green shades in its dress, while Hyla cinerea tends decidedly toward the yellow-greens.

It is unusual to see any creature displaying everywhere so even a colour. The colour may be a little deeper or a little more blue along the middle of the back, on the head, and on the tibia, but otherwise there is likely to be no variation. The flecks of orange set in the vivid green make a brilliant display under a lens, but they are too small to make any impression on the naked eye. There are no colour lines for the canthus rostralis, none for the line of the jaw or for the fold over the ear; in fact, every feature so familiar in the colour patterns of other frogs is lacking here. No other tree frog in North America shows so conspicuously the dividing line between the vividly coloured parts exposed to light and the white or colourless parts concealed in resting position. There are not only the abrupt dividing lines on the sides and along the margins of each joint of arms and legs, but on the throat and hands and feet, also, the lines are conspicuous. The white extends V-shaped in the midline of the throat to the chin; it is against this white that the hands are snugly folded. The inner margin of the tarsus and the inner toes, the inner finger and a part of the second are white; even the webs that fold between the toes lack the green. It is interesting to watch Hyla evittata take the resting position, hugging the arms and legs close to the sides, tucking the hands and feet well under, and resting the head on the hands until no trace of light colour is visible.

This tree frog is an alert and active one. It shows an interesting protective instinct, reminding one of the meadow grasshopper (Orchelimum). When it is on a branch, if an enemy approaches, it swings round to the back of the branch. Here it will continue for some time to remain invisible by moving around the limb, to the right when the enemy moves to the left, to the left when the movement of the enemy is to the right, and so on. When it is finally grasped, it may open the mouth and give a high-pitched cry.