Hirafusenuma Forest Green Tree Frog Breeding Ground

Hebusu-numa Forest Green Tree Frog Breeding Site: A Treetop Spawning Sanctuary in the Abukuma Highlands

High on the summit of Mt. Hebusu, at 842 meters above sea level in the Abukuma Highlands of Fukushima Prefecture, lies a small pond no larger than a basketball court. Yet each year, when the rainy season arrives, this unassuming mountain pool becomes the stage for one of Japan's most extraordinary wildlife spectacles. White, foam-wrapped egg masses appear on the branches of trees overhanging the water, deposited by an amphibian that defies expectation by laying its eggs not in the water itself but high in the canopy above it. This is Hebusu-numa, designated a National Natural Monument since 1941 and one of only two officially recognized breeding sites in all of Japan for the forest green tree frog.

The Forest Green Tree Frog: Japan's Aerial Spawner

The forest green tree frog, known in Japanese as Mori-ao-gaeru and scientifically as Rhacophorus arboreus, is a species native to Japan. Adults measure between 4 and 8 centimeters and display a vivid emerald-green back with golden, alert eyes. Unlike most frogs, the species spends the greater part of the year living high in deciduous broadleaf trees, descending to water only during the brief breeding season.

What makes this frog truly remarkable is its method of reproduction. From late June through early August, females clamber onto branches that hang over still water and, while several males cling to her back in a frothy embrace, secrete a viscous fluid that they whip into a foamy meringue with their hind legs. Inside this protective cocoon, several hundred eggs are deposited. The foam hardens on the outside but stays moist within, shielding the developing embryos from predators and the sun. After roughly fifteen days, the foam begins to liquefy and the freshly hatched tadpoles slip out, falling into the pond below to continue their growth. Local tradition long held these mysterious white sacs to be auspicious objects, and they were once revered under the poetic name enmei kobukuro, or "longevity pouches."

Why This Pond Earned a Rare National Designation

The forest green tree frog itself is found scattered throughout Honshu, but established, dense breeding colonies are far rarer than the species' range might suggest. Hebusu-numa offers a near-perfect set of conditions: a small enclosed body of standing water with no inlet or outlet, ringed entirely by mature deciduous broadleaf forest whose branches reach far out over the surface. The interlocking canopy provides countless suitable spawning sites, while the surrounding woodland sustains the adult population year-round.

Recognizing both the cultural fame of the species in Japan and the exceptional concentration of breeding here, the government designated the site a National Natural Monument on February 28, 1941, under the criterion for "famous Japanese animals requiring preservation, together with their habitats." Today, only Hebusu-numa in Fukushima and Ōba-numa in the Hachimantai region of Iwate Prefecture hold this specific designation. Hebusu-numa has the distinction of having maintained its protected status uninterrupted for more than eighty years.

A Village's Rescue: The Story Behind the Survival

The pond's history has not been without crisis. In 1972, ill-considered logging on the northwestern slopes coincided with a severe summer drought. The water level fell catastrophically during spawning season, and tadpoles were left stranded as the pond dried. The breeding population came perilously close to extinction. The villagers of Kawauchi responded with sustained collective action—replanting, protecting the surrounding forest, hauling water, and monitoring water levels each year. Their efforts pulled the colony back from the brink, and Hebusu-numa endures today as a living monument not only to a remarkable species but also to a community's long stewardship of its natural heritage.

The Frog Poet: A Cultural Bond with Kawauchi Village

Hebusu-numa's fame extends well beyond zoology. Kusano Shimpei (1903–1988), one of modern Japan's most beloved poets, devoted much of his work to frogs and was affectionately known as "the frog poet." After being introduced to the pond by the chief priest of Chōfukuji Temple in the summer of 1953, Kusano became a passionate champion of Kawauchi Village. He returned year after year, was named an honorary villager in 1960, and donated his personal library of some three thousand books, which villagers housed in a thatched-roof building they built together: the Tenzan Bunko. To this day, the Tenzan Festival held each July honors his memory and the deep friendship between the poet and the village he loved.

Highlights and What to Look For

Visitors who come during the right season are rewarded with an extraordinary scene. The pond itself is small and intimate, its dark water reflecting the surrounding broadleaf canopy like a polished mirror. Above the water's edge, the white foam egg masses cluster on slender branches and twigs—some at eye level, others higher up. The chorus of male frogs, a mellow rolling "koro-koro, koro-koro," echoes through the forest at dusk and after rain. Look closely and you may spot the adult frogs themselves, their brilliant green skin blending with wet leaves.

Equally rewarding is the surrounding ecosystem: dragonflies, salamanders, and a wealth of wetland insects share the habitat, and the gentle approach trail through the forest is itself a quiet immersion in the Abukuma Highlands' temperate woodlands.

When and How to Visit

The peak of the spawning season falls in mid-June, when the rainy season arrives in northern Honshu. Foam egg masses can typically be seen from early June through mid-July, with active spawning best observed in the early evening or after rainfall. Because spawning depends on temperature and humidity, sightings of frogs in the act are largely a matter of timing and luck.

Kawauchi Village has no railway station of its own. The most common access route is via Tokyo Station to Kōriyama Station on the Tōhoku Shinkansen, transferring to the Ban'etsu East Line as far as Funehiki Station, then continuing by bus into the village—roughly three and a half hours in total. By car, the Joban Expressway exit at Tomioka leads into the village in about thirty minutes. Visitors are strongly advised to confirm road and trail conditions in advance with the village office, as access has been affected in past years by typhoon damage. Sturdy footwear, rain gear, and insect repellent are recommended.

Around the Village

A visit to Hebusu-numa pairs naturally with the wider attractions of Kawauchi Village. The Tenzan Bunko, the thatched-roof library housing Kusano Shimpei's donated collection, sits in a serene woodland garden. Iwana no Sato offers fishing for char, riverside camping, and a restaurant specializing in fresh trout dishes. The village hot spring, Kawauchi-no-yu, is locally celebrated for its alkaline waters said to leave skin smooth. Nearby natural sights include Fudō Falls, the Sennō River prized for its char, and the Takatsuka Plateau renowned in early summer for its blooming red-bell flowers. For a contemporary touch, a converted 200-year-old farmhouse café in the village serves a playful "Hebusu-numa melon soda" topped with a frog-shaped gummy and whipped-cream egg mass.