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Heat fries mosquitoes for unusually pleasant July

Published: 27 Jul. 2025, 19:14

Mosquito repellents line the shelves of a supermarket in Seoul on July 25. [YONHAP]

Seoul’s usual summer swarm of mosquitoes has all but disappeared, scorched away by record-breaking heat and a shortened monsoon season.

According to the mosquito forecast — issued by the city government — remains at “attention” as of Friday, the second-lowest of its four-tier system: "pleasant," "attention," "caution" and "unpleasant." Normally by mid-July, levels rise to “caution” or “unpleasant.”

The mosquito activity index, which estimates the likelihood of bites outdoors at night, shows a steep drop. On July 19, the index hit 52.8, crept up to 65.3 on July 21, then plunged to 23.1 by July 22. A reading of 100 means a person could be bitten more than five times within 10 minutes outside at night.

Mosquitoes thrive in temperatures between 15 and 30 degrees Celsius (59 to 86 degrees Fahrenheit) and prefer steady rainfall over sudden downpours. Typically, mosquito populations surge from mid-June, peak around mid-August and gradually fade.

A female mosquito [KCDC]

But not this year.

Experts say the summer heat arrived unusually early and has remained intense. Temperatures exceeded 35 degrees Celsius in early July, drying up puddles and stagnant water — key breeding grounds for mosquitoes.

The short-lived monsoon season made things worse. Heavy rains fell in concentrated bursts, washing away potential nesting sites instead of sustaining them.

The result? Activity levels that once soared to 100 last June have yet to reach that threshold this year.

Still, health officials warn that autumn mosquitoes could come back with a vengeance. A similar pattern played out last year. After a dip during July and August due to heat and floods, mosquito activity surged again in late September, when temperatures began to ease.

Translated from the JoongAng Ilbo using generative AI and edited by Korea JoongAng Daily staff.
BY KIM EUN-BIN [[email protected]]