Sweltering heat, heavy rains drive away ‘summer mosquitoes’ in Korea

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Korea's notorious summer mosquitoes — normally a constant nuisance throughout July — have been conspicuously less visible this year, with experts attributing the sudden drop in prevalence to an unprecedented early heat wave and heavy rains.

According to daily mosquito data provided by the Seoul Metropolitan Government on Sunday, the city’s mosquito activity index stood at “caution,” classified as Level 2 on the four-phase index. Typically, by mid-July, the index escalates to Level 3 or 4.

The index is determined using a combination of the city’s real-time mosquito trapping data ― the number of mosquitoes collected daily at designated locations ― and weather factors such as temperature and humidity from the Korea Meteorological Administration.

Mosquitoes are generally active when temperatures are between 15 and 30 degrees Celsius. In addition, a climate with regular, periodic rainfall is considered optimal for mosquitoes, as it provides steady breeding sites.

But this year, the heat wave arrived earlier than usual, with temperatures surpassing 35 degrees Celsius as early as June. This dried up stagnant water or puddles where mosquitoes lay their eggs. Additionally, the brief monsoon season and sudden heavy downpours further reduced mosquito-friendly environments, experts say.

The numbers back up these observations. In June of last year, the mosquito activity index frequently hit the maximum mark of 100. The index mostly remained between Level 2 and 3 (25-75) during the same period this year.

However, there are growing concerns about a possible surge of “autumn mosquitoes.” Last year showed a similar weather pattern marked by repeated cycles of heat waves and sudden heavy rains, and mosquito activity peaked in June and increased again in late September.