The Encyclopedia Americana (1920)/Tree-frog
TREE-FROG, or TREE-TOAD, a frog of the family Hylidæ, distinguished from common frogs (Ranidæ) by having the ends of the fingers and toes dilated into flattened discs or suckers, which enable them to lead their peculiar arboreal life. They are of more elegant form, smaller size, brighter colors and more active habits than the Ranidæ, and are lively during the day; they feed on insects, which they pursue on bushes and trees, stealing toward them or suddenly springing and swinging upon them; they climb like geckos, and by the same mechanism; the lower surface of the discs is endued with a viscid secretion, by means of which they can walk with the body suspended from the under parts of leaves and other smooth bodies; the skin is mostly smooth upon the back, but on the abdomen and inside of legs thickly studded with small warts or tubercles. They possess to a remarkable degree the faculty of changing color, by the modifications of the contents of the pigment cells under the skin (see Chromatophores), no doubt a provision to enable them to elude their numerous enemies. They are very clamorous, and particularly noisy at the approach of rain. In winter they bury themselves in the earth or in the decayed wood and dust of old stumps. They breed in the spring, depositing their eggs in the water. The species are numerous, especially in tropical America.
The common tree-frog of North America (Hyla versicolor) resembles a toad in form, but is more flattened; body short and warty above, the color varying from pale ash to dark brown, with several large irregular blotches of greenish brown, white and granulated below, and abdomen yellowish near the thighs; the colors vary at the will of the animal. The head is short and rounded, the mouth large, with teeth on upper jaw and vomer; eyes large and brilliant, the iris bright golden; there are four fingers and five toes, both ending in viscous pellets, the former distinct, but the latter webbed. It is about two inches long, and is found abundantly as far west as the Mississippi, on decaying trees and about old fences of wood or stone, the color of which it nearly resembles. It is very noisy in spring and summer toward evening, especially in cloudy weather, and its cheerful and abruptly terminating note must be familiar to all residents in the country. This species in the Southern States is replaced by the green tree-frog, which is bright green above, yellowish white below, with a straw-colored lateral line extending from the upper jaw over the shoulder and along the side; it is shorter and more slender than the northern species, and is most commonly seen about broad-leaved plants, especially Indian corn, the color of the leaves of which it greatly resembles, concealed during the heat of the day, but coming out morning and evening and becoming very active and noisy; the single note is clear and bell-like. The tree-frog of Europe (H. arborea) much resembles this. Several other species occur in the Southern and Southwestern States. In the genus Acris the locomotive discs are less developed and the limbs more slender than in Hyla, and there are teeth on the palate instead of the vomer. The A. gryllus, or cricket, is about one and one-half inches long, with an elongated pointed head, a triangular dusky spot between the orbits; body ashy above, with a green and sometimes reddish dorsal line, and three oblong black spots margined with white on the sides. It is a lively species, constantly chirping like a cricket, even in captivity. In the genus Hylodes the palate is toothed, and the slender fingers and toes are free, with small discs. Pickering's tree-frog (H. pickeringii) is nearly an inch long, with short head and yellowish brown body, with dusky rhombodial spots and lines, sometimes like the letter X on the back; pale flesh-colored below, tinged with yellowish on the throat. This is the true peeping frog, the noise being made by both sexes; in summer they cease to be vocal, retiring from the pools where the eggs were laid to the woods, where they live on trees, hopping about on the branches in search of insects and occasionally uttering a shrill whistle.
Many strange variations in breeding-habits and rearing of young characterize the tree-frogs of tropical America, which exist in a great number of genera and species. A famous South American species is the ferreiro (H. faber), which makes small pens or nurseries under water in which its eggs are left to hatch, and where the tadpoles are confined, protected from many dangers. Another species (H. goeldii) carries its few large eggs on its back until they hatch, and the young remain some time afterward. The genus Nototrema develops pouches in the skin of the back of the female in which the eggs snd young are safely transported. Extensive information and guidance to further facts may be found in the ‘Cambridge Natural History’ (Vol. VIII, London 1901).