"Rain and bugs are falling from the sky together."
"Bugs fell on the tteokbokki and fish cakes, so I had to throw away all the food."
On May 27 at Jamsil Baseball Stadium in Songpa-gu, Seoul, thousands of Oriental mayflies — commonly known as "Tinkerbells" — swarmed the stadium as the floodlights came on for a night game. Spectators repeatedly swatted away insects that flew at their faces, while bugs rained down on food stands. With rain falling at the same time, the professional baseball broadcast showed a bizarre scene of insects and raindrops pouring down together.
This may be just the beginning. As unusually high temperatures this summer are expected to drive larger-than-usual outbreaks of various insects — including Oriental mayflies, lovebugs, and gypsy moths — public discomfort is set to grow.
According to the Ministry of Climate, Energy and Environment, the National Institute of Biological Resources, and the National Institute of Ecology on Tuesday, mass outbreaks of various insects are expected through September this year. The unusually warm weather that began in April has accelerated larval growth and raised the survival rate to adulthood.
Insects are cold-blooded animals that cannot regulate their body temperature, making them directly affected by changes in air and water temperature. The higher the temperature, the shorter their growth cycle and the faster they reproduce.
◇ 'Tinkerbells' Cover Jamsil — A Paradox of Cleaner Han River
The first major outbreak of the year is the Oriental mayfly. From last fall through this spring, over a period of roughly eight to nine months, the mayflies grew as larvae in waters such as the Han River and Tancheon Stream, and have been emerging as adults in large numbers since May.
Jamsil Baseball Stadium has become a major hotspot for Oriental mayflies because it is located near the Han River and Tancheon, and uses powerful floodlights during night games. The light-loving adults flock to the stadium.
Oriental mayflies, however, do not bite humans or transmit diseases. Once they reach adulthood, their mouthparts degenerate, leaving them unable to feed. The problem lies in the visual revulsion and inconvenience caused by their swarming behavior.
Interestingly, the surge in numbers in central Seoul stems from a paradox: improved water quality in the Han River. Oriental mayfly larvae live in clean water of Class 2 quality or better. As Han River water quality has improved, their habitat has expanded, and combined with this year's unusually high temperatures, the population has exploded, analysts say.
◇ Lovebugs Next — Gypsy Moths and Metcalfa Planthoppers Also on Alert
Following the Oriental mayfly, a mass outbreak of the red-backed velvet fly — commonly known as the "lovebug" — is expected in June and July.
First observed in large numbers in 2022 in Seoul's Eunpyeong-gu and the Bukhansan area, lovebugs have since expanded their range across the entire Seoul metropolitan area. Domestic populations are believed to have likely originated from China's Shandong Peninsula. Experts say the rising winter temperatures in recent years have improved the overwintering success rate of larvae, leading to a rapid increase in numbers.
In the height of summer, July and August, the gypsy moth — a pest — is also a concern. Gypsy moth caterpillars devour the leaves of forests and street trees in large quantities. The fine toxic hairs on their bodies cause dermatitis and itching in humans, and the wing dust of the adults also causes contact dermatitis.
In autumn, from September to October, the invasive Metcalfa planthopper may also emerge in large numbers. The Metcalfa planthopper is a pest that sucks the sap of crops and street trees and causes sooty mold disease. With no clear natural predators in Korea, its population tends to grow rapidly.
◇ "Missing Typhoons Fueled the Unwelcome Guests"... Government Launches Eco-Friendly Pest Control Push
Experts cite climate change as the cause of the recurring insect outbreaks. With global warming, larval growth has outpaced the predation rate of natural enemies, temporarily disrupting the ecological balance.
"The buffering function of the ecosystem has been temporarily paralyzed," an official at the National Institute of Biological Resources said.
The fact that not a single typhoon made landfall in Korea last year also played a role. Typhoons and torrential rains usually wash away larvae in rivers and naturally regulate populations, but this process barely occurred last year.
The government plans to expand eco-friendly pest control methods instead of relying on chemical agents.
To curb Oriental mayflies, work is underway to replace urban lighting with yellow-toned LEDs, which insects find less attractive. Floating traps that lure insects with bright light and then spray water to wet their wings and remove them are also being installed along the Han River.
For the red-backed velvet fly, the government is reviewing a plan to spray soil bacteria — used to control mosquito larvae — in areas where outbreaks are expected.
