Autumn mosquitoes are running rampant. Mosquitoes originally were active mainly in summer. With recent climate change bringing abnormal heat, mosquitoes have decreased in summer and are breeding in autumn.
According to the Seoul Institute of Health and Environment on the 16th, 16,997 mosquitoes were collected from April to the second week of November last year. Of those, 9,234 were caught in autumn (September–November), accounting for 54% of the total. That is 38% more than the 6,691 mosquitoes in summer (June–August). This trend is expected to continue this year.
As a poikilotherm, the mosquito feeds on human blood and is highly active at 26–27 C. When the temperature exceeds 30 C, its body temperature rises and it dies quickly. Lee Dong-gyu, a professor in the Department of Public Health and Environmental Science at Kosin University, said, "A mosquito's lifespan is three weeks at 26–27 C and shortens to two weeks at 30 C or higher."
According to the Korea meteorological Administration, the nationwide number of heat wave days this summer with daytime highs over 33 C was 28.1. That was 17.5 days more than average, making it difficult for mosquitoes to inhabit.
The monsoon season also had an effect. Mosquitoes lay eggs in standing puddles. This summer, the monsoon was short, and many puddles dried up. Even when it rained, the downpours were localized, sweeping away larvae and making breeding difficult.
As autumn set in, temperatures dropped to levels favorable for mosquito activity. Professor Lee said, "In the past, mosquitoes were abundant in June–August, but recently the weather during that period has been hot and the ground has dried out, so mosquitoes have been increasing only after September."
Experts expect mosquitoes to remain active for the time being. Cold winds must blow for mosquito activity to wane. Mosquitoes do not feed on human blood below 13 C. When it falls below 5 C, they cannot fly and overwinter.
Lee said, "The Asian tiger mosquito that is commonly seen around us overwinters as an adult," adding, "When body temperature drops, metabolic activity also decreases, and while maintaining only life, it endures 4–5 months until spring in places like basements and subways."
However, apartments and buildings are warm due to indoor heating, so mosquitoes can awaken and be active even in winter. Lee said, "If indoor spaces are warm, flight and blood feeding are possible (even in winter)."
Mosquitoes can be repelled with repellents containing diethyltoluamide (DEET). Mosquitoes find people by the smell of sweat, but repellents numb their sense of smell. The effect lasts 4–5 hours. However, DEET can cause adverse effects on the nervous system. The Ministry of Food and Drug Safety recommends using mosquito repellents with 10% or less DEET for those 6 months and older, and 10–30% repellents for those 12 and older.