The forecast for the emergence of the “fall webworm,” an invasive pest native to North America, was raised to the “caution” level last month. The larvae of this moth species feed on the leaves of street and landscape trees, causing significant public nuisance when outbreaks occur.

Although the fall webworm was first introduced to Korea in the 1950s, the damage it causes has intensified in recent years. With rising spring and autumn temperatures extending the insect’s active period, experts say it may now be capable of reproducing up to three generations per year. The damage caused by the second generation of larvae is predicted to reach 26.9 percent this year, nearly four times the estimated 6.7 percent damage level from the 2010s.

Climate change is accelerating the invasion of foreign “emergency pests,” a term used for insect populations that suddenly explode and damage forests or crops. These pests can include both native and non-native species, but most recent cases involve foreign insects.

According to the National Institute of Ecology’s “National Survey on Invasive Species Habitats of 2024” released on August 4, a recent survey in the Gyeonggi and Gangwon regions confirmed the presence of 32 invasive insect species. This included four species officially designated as “ecosystem-disrupting organisms,” such as the brown marmorated stink bug. Similar surveys found 79 invasive species in the Yeongnam region in 2023 and another 79 in the Chungcheong and Honam regions in 2022.

To date, the Ministry of Environment has classified 210 insect species as invasive. While not all non-native insects are harmful, rapid population growth can lead to serious consequences. One notable example is Plecia longiforceps, commonly known as the “lovebug,” which has rapidly spread across the Seoul metropolitan area in recent years. Although generally considered a beneficial insect, its massive outbreaks have led to it being increasingly perceived as a pest.

Notably, all of the “emergency pests” identified by the Korea Forest Service and the Rural Development Administration, such as the spotted lanternfly, white planthopper, and brown marmorated stink bug, are invasive species. The white planthopper, native to North America, feeds on leaves during its larval stage and sucks sap as an adult, damaging trees. The spotted lanternfly, originating from China, feeds on the sap of fruit trees like grapes and pears, causing sooty mold through its excretions. The brown marmorated stink bug, also from China, drains sap and causes branches to wither and die.

Subtropical insect species are also beginning to enter Korea. A prominent example is the Anoplophora chinensis, first identified in Jeju Island in 2019. It was confirmed to have settled in Korea by 2022, and by 2023, more than 1,000 adult specimens were captured in the Yongyeon Valley of Jeju. This species is known to damage camphor and camellia trees. While currently limited to Jeju, the National Institute of Forest Science warns that its habitat could expand to the southern coastal areas of the mainland.

To assess the likelihood of large-scale infestations, the National Institute of Forest Science is conducting studies analyzing climate suitability for more than 200 invasive insect species. Nam Young-woo, a researcher at the institute, said, “In the early stages of invasion, these pests have limited distribution and can be eradicated, but once they adapt to the domestic climate and spread, control becomes extremely difficult.” He added, “Climate change is expanding the geographic range of these pests, and the risk of new subtropical species entering and settling is growing. Preemptive measures are urgently needed.”