Fatoua villosa is an annual herb in the Moraceae (mulberry) family. Common names include mulberry weed, crabweed, or hairy crabweed in English, kuwakusa (クワクサ; 桑草) in Japanese, and shuǐ shémá (水蛇麻) or xiǎo shémá (小蛇麻) in Mandarin. It is native to Eastern Asia, some Pacific islands, and parts of Australia, including in two Australian states (Western Australia and Queensland), the Bismarck Archipelago, China, Indonesia (Java, Maluku, Sulawesi and the Lesser Sunda Islands), Japan, Korea, New Guinea, the Philippines, the Solomon Islands, Taiwan, Thailand and Vietnam. It has become an invasive species in the United States where it grows in disturbed areas such as flowerbeds, greenhouses, and agricultural fields.