"Japanese" Invasive Species Spreading Across the U.S., Causing Problems for Insects and Wild Plants
By Hiroko Nishimura, Directorate General for the Americas
November 14, 2024

Nikkei, a leading Japanese business and financial publication, interviewed Newtown Knotweed Initiative's Christine St. George for this story on knotweed.

Insects and wild plants originating from Japan are proliferating in the United States. Due to factors such as global warming, there have been a number of reports of these insects spreading to areas that had previously been less affected. Efforts have also begun to curb the increase in these so-called "Japanese" plants and animals.

"Japanese Giant Spider Attacks on the Wind." A sensational headline appeared on a local news site in the United States in the early summer of 2024. This was the Joro spider, which lives widely in Japan from Honshu to Kyushu. Its yellow and black appearance and the way it moves on the wind using its strong silk have aroused fear and curiosity among local residents.

The orb spider is thought to have landed in the United States about 10 years ago, hidden inside cargo containers. Its habitat, which was confined to the southern state of Georgia until a few years ago, has been expanding rapidly since then. It was first spotted in the New York City area in the summer of 2012, sparking a fuss over a "giant spider invasion."

However, the venom of this spider is said to be virtually harmless to humans. Professor Andy Davis of the Odum School of Ecology at the University of Georgia, who studies the ecology of the orb spider in the United States, explains, "The spiders native to the east coast of the United States are small and dull in color. The orb spider is a beneficial insect that is mostly harmless to humans, but it has been written about in a humorous way because of its novelty."

The threat of home-destroying "demons" The devil's plant that preys on your house - The Wall Street Journal featured Japanese knotweed in September. It grows quickly and spreads by underground stems, making it difficult to completely remove, and there are concerns that it could damage building foundations and asphalt.

Japanese knotweed is a perennial plant of the Polygonaceae family that is widespread in Japan. In some areas, it is called "skanpo" and is edible. It was brought to the United States in the 1800s and has grown in large numbers in the southern and central parts of the country. In recent years, reports of mass proliferation have been reported in the northern states of the East Coast, causing headaches for local residents.

In 2011, residents of Newtown, Connecticut, who could no longer tolerate the proliferation of Japanese knotweed, formed a countermeasure group called the Newtown Knotweed Initiative. They collect sightings from neighbors and work to remove the weeds. Member Christine St. Georges (46) is enthusiastic, saying, "We want to raise awareness of proper removal methods."

The Japanese beetle, which likes to eat soybean leaves and causes damage to agricultural crops, landed on the east coast of the United States in the 1910s and has gradually expanded its habitat westward. Michelle, a 70-year-old living in Boulder, Colorado, said about the Japanese beetle, "I suddenly started seeing them in my garden about 5-6 years ago, and they've been causing damage to roses and other crops."

It has also begun to spread to states on the West Coast. In the northern state of Washington along the Pacific coast, three were confirmed for the first time in 2020, but in 2021, more than 20,000 were found. "If you see any of these insects, please report them," said the state's Agriculture Department, which has set up a dedicated hotline during the crop growing season this year as well, calling for information.

The origin is not limited to Japan. The University of Georgia's Invasive Species Information Site lists 48 invasive species as "Japanese." However, Japanese knotweed and orb spiders are actually native to East Asia, not just Japan.
Some point out that the influence of climate change, including global warming, is behind the spread of invasive species that have adapted to high temperatures and humidity in the U.S.

Dr. Erica Kistner-Thomas, who leads the research team for plant ecosystem protection at the U.S. Department of Agriculture, predicts that "if the trend toward global warming continues, the Japanese beetle problem will spread further into the northern U.S. and Canada."

Jeremy Andersen, an assistant professor at the University of Massachusetts Amherst, also points out the effects of climate change as the reason for the increase in Japanese knotweed on the eastern part of the East Coast, saying, "Recent weather conditions, such as floods and warm winters, have favored Japanese knotweed, which has a stronger reproductive ability than native plants."

Assistant Professor Andersen has been working on an experiment since 2020 to import and release the Japanese insect "Itadori var. nigricans," a natural enemy of Japanese knotweed, to manage its reproduction. "It is difficult to completely eliminate invasive species. Ideally, we would like to settle on a more balanced coexistence with native plants," he said, expressing his hopes for the new method.