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 Sara Yajima, a light-novel author and member of the "Frog Friends Society" (Kaeru Tomo no Kai), a group of frog enthusiasts based at the Kawanabe Kyosai Memorial Museum of Art in Kawaguchi City, Saitama Prefecture.

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 (Amagaeru): The classic sound of the rainy season—it croaks "gero-gero" or "kero-kero" before and after rain.
• American Bullfrog (Ushigaeru): Known for its deep, low "bwoh" call. Though an invasive species, it's now established throughout Japan.
• Tonosama Frog: Common in rice paddies, where it helps farmers by eating agricultural pests.
• 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," frog figurines placed in wallets or shops are believed to bring financial 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 Deities: Tsubaki Grand Shrine in Mie Prefecture and other shrines around the country have spots dedicated to frogs.

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.
• Natural Predators: Frogs are eaten by snakes, herons, raccoon dogs, and many other animals, playing an important role as a mid-level predator in the ecosystem.