In Okayama Prefecture, when humid air settles over a stream, hotaru—Japan's fireflies—begin signaling. On warm, windless evenings, they often start glowing about two hours after sunset under favorable conditions, inviting silence beside water.

Fireflies aren't flies but beetles, and most species stay near water—ponds, streams, marshes, and rivers. By day they hide low in the grass; after dark they climb vegetation and take flight, flashing to find a mate. Their light comes from a chemical reaction in the abdomen, and species-specific timing helps partners recognize the right signal. Their young live a quieter, hungrier life: larvae are carnivores that feed on soft-bodied prey such as snails and slugs. Adults may eat insects, nectar, or pollen.

In Japan, watching them—hotaru-gari—has deep roots. Heian-era (794–1185) writers like Sei Shōnagon wrote about fireflies, and later literature and ukiyo-e art—a traditional form of woodblock prints and paintings—used their brief light to evoke impermanence.