A fall webworm (Courtesy of a reader)

Concerns are growing about the growing presence of fall webworms, which are not harmful to humans but can damage trees, spotted more frequently across the country this month.

Several social media users have also expressed their complaints about the fall webworms especially at Han River parks. One user on X -- formerly known as Twitter -- wrote, “If you’re visiting Han River, make sure to bring a tent or bug spray. These caterpillars have taken over the park.”

Seoul Facilities Corp. has significantly increased its pest control operations near Han River to counter the fall webworms. However, this has its own limitations given the prohibition of pesticide use along the river.

Instead, a high-pressure water spray method is employed to dislodge the webworms from the trees, allowing the corporation to clean up later. Cheongju in North Chungcheong Province and Ilsan in Gyeonggi Province are also conducting special pest control operations five times a week.

Fall webworms, which are caterpillars of the fall webworm moth and native to North America, feed on leaves and branches, damaging trees in urban areas and fruit trees in farmlands.

Many fall webworms have not just been spotted around Seoul but also in Gyeonggi Province, North Chungcheong Province, North Gyeongsang Province and North Jeolla Province, according to Korea Forest Service in August.

For the first time since 1958 -- when fall webworms were first believed to have been spotted in South Korea -- Korea Forest Service upgraded its outbreak forecast in August from Level 1 “Attentive” to Level 3 “Alert.” The “Alert” level is issued only when pests spread to two or more regions across the country or cause more than 50 hectares of damage.

X users express their complaints about the increase in fall webworms in Han River. (X)

Compared to last year, researcher Kim Min-jeong from the National Institute of Forest Science said that the damage caused by fall webworms has doubled from 12 percent to 27-28 percent this year.

“An increase in fall webworm numbers this year suggests a potential trend for more of them to come in the coming years,” said Kim in an interview with Yonhap News Agency. On average, one fall webworm moth lays about 600 eggs before it dies. As the webworm numbers have significantly increased this year, Kim believes there will likely be more of them in the coming years due to rising fall temperatures.

“While it is difficult to conclude that the increase in webworm numbers is due to extreme weather conditions, a one to two-degree increase during this year’s fall season temperatures could also be a contributing factor,” added Kim.