Microseason: Silkworms Wake to Eat Mulberry Leaves
SUMMER
APPROACHING ABUNDANCE
SILKWORMS WAKE TO EAT MULBERRY LEAVES
21 - 25 May
This late May microseason marks the moment when silkworms awaken and begin to feed on fresh mulberry leaves. This is not merely a biological observation but a cultural marker, announcing the beginning of Japan’s traditional sericulture, the cultivation of silkworms and the production of raw silk.
At the center of this cycle is not the silkworm itself, but kuwa. The mulberry tree. Without which sericulture would not exist, as the domesticated silkworm feeds exclusively on mulberry leaves. Silkworm and mulberry are raised together as a singular ecosystem. The leaves had to be picked at just the right age and freshness. The nutritional needs and physical ability of the larvae change as they molt and grow so the lifestage of the mulberry leaves need to be selected as such. This means soft, tender foliage for young larvae, and tougher and more fibrous leaves for their final growth stage.
In regions like Gunma, Nagano, Yamanashi, and Yamagata where sericulture flourished, mulberry cultivation became a year-round endeavor. Farmers pruned the trees to encourage optimal leaf growth, and various local cultivars emerged over time. In Gunma Prefecture, the Ichinosé variety was especially prized for its high nutritional value and rapid regrowth. In Nagano, the Kairyou-Nezumigaéshi variety was developed for improved disease resistance and leaf yield. These cultivars, refined through generations of agricultural experimentation, represent a critical but often overlooked dimension of Japan’s material heritage.
This microseason corresponds to the appearance of the year’s second flush of mulberry leaves, following the first leafing in early Spring. By this time, the trees have produced leaves with the optimal balance of moisture and nutrients. Farmers once measured this readiness by the color and pliancy of the leaves and the rhythm of surrounding insect life. Leaf gathering during this season was an intensive process. Entire households, often with help from the entire community, worked day and night to hand-pick leaves and feed the silkworms' vivacious appetite.
The height of Japan’s traditional sericulture industry occurred between 1800s and into the early 1900s, particularly peaking in the Taisho era (1912–1926). This period coincided with Japan’s growing role in global trade. By the 1930s, Japan had become the world’s largest exporter of raw silk, earning the nickname “white gold”, supplying markets in the United States, Europe, and China. Regions such as Gunma, Nagano, Yamanashi, and Fukushima were major centers of sericulture, supported by a network of family-run farms, cooperative silk-reeling stations, and national agricultural extension programs. The domestic demand for silk in traditional garments such as kimono also sustained production. Following World War II, the rise of synthetic fibers, population shifts into urban areas with greater capital, the strengthening currency making foreign silks more cost effective, and lifestyle changes with a movement away from traditional Japanese clothes, all contributed to the industry's gradual decline.
Sericulture still survives in small-scale, heritage-focused operations. Local governments and institutions such as the National Agriculture and Food Research Organization (NARO) and the Tomioka Silk Mill, now a UNESCO World Heritage Site, continue to document, preserve, and promote traditional silk production. Some regions, such as Gunma Prefecture’s Usui District and Nagano’s Ueda City, have retained knowledge of mulberry cultivation and silkworm rearing, often in collaboration with artisans and cultural preservation groups. These efforts sustain a living memory of a once-central part of Japan’s rural economy and material heritage. Though Japan’s commercial silk industry has declined in scale, mulberry trees still dot the landscape in former sericulture regions. Some have grown wild, others are maintained by individual artisans or research institutes.
Mulberry trees also continue to appear in folk songs, regional festivals, and children’s stories. The tree is tied to the spiritual image of the silkworm as a sacred creature, its life seen as a gift nourished by the mulberry leaf. In this way, the mulberry tree is more than a food source, it is a symbol of care, continuity, and material memory. The expression “we’d even borrow a cat’s paw” which is still very much used in everyday language, spawned not only to describe the overwhelming labor involved in caring for silkworms, but also referencing cats kept in silkworm houses to guard against pests.
Photo credit: Shimoda Tourism Agency