United States

From the USPS press release:  "Frogs live on every continent except Antarctica; more than 90 species live in the United States, including the four on these stamps. Found throughout the western United States, the tiny Pacific tree frog (Pseudacris regilla) is nicknamed the “Hollywood frog.” Countless television shows and movies have used its rib-bit, rib-bit call in nighttime scenes. The northern leopard frog (Rana pipiens) is commonly identified by its highly distinctive call, a rattle-like snoring noise, followed by several notes described as “chuckling” or “clucking.” Sometimes called the rain frog for its noisy choruses after a warm rain, the American green tree frog (Hyla cinerea) is also dubbed the cowbell frog for the sound of its short call when heard from a distance. A raspy, quack-like call much like the scolding noise of a gray squirrel identifies the squirrel tree frog (Hyla squirella), found from southeastern Virginia through Florida and along the Gulf Coast to Texas. Working with a green color palette and touches of brown, artist Nancy Stahl captured the defining features of each frog making them recognizable. Art director William J. Gicker designed the stamps. The Frogs stamps are being issued as Forever stamps and will always be equal in value to the current FirstClass Mail 1-ounce price."