Frog Day (Kaeru no Hi)

What is Frog Day?

June 6th is "Frog Day" (Kaeru no Hi) in Japan. The date comes from a play on sounds: "6" can be read as "kero," and "kero-kero" is the classic onomatopoeia for a frog's croak in Japanese—so "6/6" reads as "kero-kero," mimicking a frog's call. The day was established in 1998 by writer Sara Yajima, a member of the "Frog Friends Society" (Kaeru Tomo no Kai), a group of frog enthusiasts based at the Kawanabe Kyosai Memorial Museum in Warabi City, Saitama Prefecture, which holds events such as frog exhibitions.

The Deep Connection Between Frogs and the Rainy Season

June falls right in the middle of Japan's rainy season (tsuyu). This is the time of year when frogs in rice paddies and wetlands begin croaking all at once, reminding people of just how familiar a presence frogs have been in Japanese life since ancient times.

• Japanese Tree Frog (Nihon Amagaeru): The classic sound of the rainy season. Its Japanese name, "rain frog," comes from its habit of calling when rain is approaching.
• American Bullfrog (Ushigaeru): Known for its deep, low "bwoh" call. Though an invasive species, it's now established throughout Japan.
• Tonosama Frog (Black-spotted Pond Frog): Lives in rice paddies and eats insects and other small creatures. Its numbers have been declining in many areas.
• Forest Green Tree Frog (Moriaogaeru): A frog native to Japan that lays its eggs in white foam masses on tree branches.

Frogs in Japanese Culture and Folklore

In Japan, frogs have long been considered a lucky animal because of wordplay: "kaeru" can mean both "frog" and "to return/come home," and also evokes "money coming back" (お金がかえる).

• Safe Travels: Because "kaeru" can mean "to return home safely," frog motifs are used in charms to wish for safe travel.
• Good Fortune With Money: Because "kaeru" can also suggest money "coming back," some people keep frog charms in their wallets for luck.
• Matsuo Basho's Haiku: "An old pond / a frog jumps in / the sound of water" is one of the most famous haiku in Japanese literature.
• Frog Statues at Shrines: Futami Okitama Shrine in Ise, Mie Prefecture, has many frog statues offered by visitors, carrying wishes such as returning home safely.

Frog Biology

• Metamorphosis: Frogs are amphibians that undergo dramatic metamorphosis, growing from egg to tadpole (larva) to adult frog.
• Skin Respiration: In addition to breathing with their lungs, frogs also breathe through their skin, which is why they need to keep their skin moist at all times.
• Hibernation: Many species hibernate in the soil or under fallen leaves and wake up in spring.
• In the Food Chain: Frogs eat insects and other small creatures while also serving as food for snakes, herons, and many other animals, playing an important role in the ecosystem.