In Japan one can only cultivate silkworms in the summer; in the winter, one must provide them with an expensive manmade feed that they are reluctant to eat. With the exception of Hainan Island, year-round cultivation is impossible in China, too.
北國日本只能在夏天養蠶，冬天必須餵食人工飼料，既昂貴，蠶寶寶又不太肯吃；中國大陸除了海南島外，也沒有四季種桑養蠶的條件。