Learning urban beekeeping on a Tokyo building rooftop: The Marunouchi Honey Project

On May 20, designated as World Bee Day, an event to learn about urban beekeeping and the surrounding natural environment was held on the rooftop of the Otemachi Building, located in Chiyoda City at the very heart of Tokyo. It was organized by the Marunouchi Honey Project Executive Committee and other partners. The event drew approximately 500 participants, including workers from nearby companies and local nursery school children. Through tours of the apiary and a tasting session comparing honey harvested from the Marunouchi area, attendees experienced the richness of urban nature and the changing of the seasons.

Imperial Palace and Hibiya Park fall within the bees' foraging range.

The business district encompassing the Otemachi, Marunouchi, and Yurakucho areas is collectively known as ?Dai-Maru-Yu.? This district features roadside trees, green spaces, the Imperial Palace, and Hibiya Park within a 2-to-4-km radius, which is considered the foraging range of honeybees. Here, a wide variety of herbs and trees burst into bloom. The Marunouchi Honey Project Executive Committee was established in July 2016 as an initiative aimed at building a community within the district through urban beekeeping, striving toward a city that coexists with nature. Every year from late April to early August, the project monitors the health of the honeybees and the accumulation of nectar in hives located on the building's rooftop. The harvested honey is then supplied to local restaurants and hotels within the area. In fiscal 2025, approximately 800 kg of honey was harvested.

As of May 2026, a total of around 30 beehives are arranged on the rooftop of the Otemachi Building, stacked in groups of two or three. Each hive (measuring roughly 40 cm long, 50 cm wide, and 30 cm high) contains 9 to 10 frames, meaning the project effectively manages about 10 distinct colonies of honeybees.

During the apiary tour, guides explained the presence of worker bees, queen bees, and drones, and described where the workers gather nectar. Pulling a frame densely covered with bees out of a hive, a guide noted, "When it's crowded on both sides, there can be up to 2,000 bees gathered here. Once it fills up with honey, it can weigh as much as 2 to 3 kg." The guide then let the visiting children hold the frame so they could experience its weight firsthand.

Rapeseed, cherry blossoms, and privet: A shifting source of nectar

The venue also featured a booth where visitors could experience differences in the color and flavor of the honey depending on when it was harvested. Tasting and comparing honey collected on April 9, April 30, and May 14 revealed distinct profiles: the honey from April 9 possessed a brilliant aroma and sweetness, while the honey from April 30 and May 14 offered a refreshing fragrance coupled with a subtle, light sweetness.

Honeybees begin working around the time rapeseed flowers start blooming. In April, their focus centers primarily on cherry blossom nectar, before shifting to the flowers of privet trees lining the city streets from May onward. The pollen DNA contained in the honey was analyzed during fiscal 2025. Mainly 14 plant genera groups, including the genus Acer (maples) and the genus Brassica (mustards/rapeseed), were identified, with their frequency of appearance shifting along with the seasons.

Alongside its beekeeping efforts this fiscal year, the Marunouchi Honey Project is running an initiative until November 30 to collect photographs and information on flowers and the insects that visit them via a smartphone app. By investigating which types of insects gather on specific flowers and perform the role of transferring pollen from stamens to pistils, the project aims to utilize the findings to help plan future planting efforts throughout the Dai-Maru-Yu area.