The "flying" frog is a frog that has the ability to glie. That is, it can descend at an angle of less than 45° relative to the horizontal. Arboreal frogs (non-flying frogs) can also descend vertically, but only at angles greater than 45°, which is referred to as parachuting. Flying frogs have evolved independently among 3,400 species of frogs from both New World (Hyla) and Old World (Rhacophoridae) families and their evolution is seen as an adaptation to their life in trees, high above the ground. Characteristics of the Old World species include "enlarged hands and feet, full webbing between all fingers and toes, lateral skin flaps on the arms and legs, and reduced weight per snout-vent length". These morphological changes contribute to the flying frog's aerodynamic abilities. Alfred Russel Wallace made one of the earliest reports of the flying frog, from observations in the Indo-Malayan region . The species he observed was later termed Wallace's Flying Frog (Rhacophorus nigropalmatus). They have suction pads on their webbed feet which helps their balance in the high trees that they live in.