Scorching heat suppresses mosquito activity, but experts warn of a delayed resurgence
If you live in South Korea, this year's summer might have felt strangely quiet.
The familiar high-pitched buzz of mosquitoes, long considered a seasonal nuisance, has been noticeably absent.
But experts say the reprieve may not last, with a possible resurgence of mosquitoes looming as the season transitions into autumn.
This year’s extreme weather, marked by an unusually early and prolonged heat wave, a shortened monsoon season, and bursts of torrential rain, has disrupted the mosquito life cycle here.
The earlier-than-expected heat wave has dried up stagnant water, an essential breeding ground for mosquitoes. And rather than replenishing them, the heavy rain might have further destabilized mosquito habitats.
While last year’s mosquito activity index reached its summer peak in June, this year’s figures have yet to.
Over the past week, the mosquito activity index, operated by Seoul's municipal government, hovered in between the mid 30s and the mid 40s until a spike in the figure to mid-50s on Tuesday, The trend is significantly below last summer’s figures when the index hit 100 from June 2 to July 1.
The index, which runs on a scale of 0 to 100, indicates the likelihood of being bitten. If the index recorded 100, there is a likelihood of being bitten more than five times during 10 minutes of outdoor activity at night.
The highest mosquito activity recorded this year was on June 28, at a relatively mild 77.2. while the activity index on July 10 dropped to zero — unprecedented for the time of year.
But this does not mean the sweltering heat leaves the mosquitoes with zero chance of survival this year.
Experts warn that mosquitoes might make a late comeback in the fall. With mosquito season becoming delayed due to weather anomalies, some worry that activities could spike once temperatures cool down again — to the level optimal for the pests to thrive.
“Just because the mosquito numbers were down during the summer doesn’t mean the season is over,” said an official from the Korea Disease Control and Prevention Agency. “There’s a real possibility of increased mosquito activity in early autumn, especially if temperatures remain mild.”
Mosquitoes thrive in mild, humid weather, around 25 degrees, and they are most active between 15 and 30 degrees.
Similar patterns seen last year could be observed again. In 2024, mosquito activity remained unusually high around September and October.
The number of mosquitoes collected through Seoul's digital mosquito monitoring system — involving 54 different locations in the capital — in October stood at about 80 percent of that of September. In the decade leading up to to 2024, mosquito activity levels had usually halved in the weeks transitioning into October from September.
The 2024 data also indicated that mosquitoes remained active until the end of November.
In preparation, Seoul city officials continue to advise residents to take preventive steps based on the mosquito forecast. While the current index remains low, fall’s approaching conditions could quickly reverse the trend. Experts recommend eliminating standing water around homes, repairing window screens, and using protective measures like mosquito nets and repellent.
For now, the heat has offered an unexpected reprieve. But as the seasons turn, South Koreans may yet face a delayed visit from summer’s most persistent pest.
jychoi@heraldcorp.com
