"Why Are There More Mosquitoes as Summer Ends?"... The Reason Behind the Surge of Aggressive September Autumn Mosquitoes

Mosquitoes Struggle to Survive Above 35 Degrees, Populations Drop in Heatwaves
In Autumn Breeding Season, Mosquitoes Feed More Aggressively

Mr. Cho (51), a resident of Yeongtong-gu, Suwon, has found himself getting bitten by mosquitoes much more frequently since the end of August. He said, "Every evening when I go out for a walk with my pet dog, I always get bitten two or three times," adding, "Even though I keep moving, the mosquitoes still bite me, and the itchiness lasts longer than usual."

AI image reconstructed based on a reader's story. ChatGPT

Mosquitoes, which had retreated during the heatwave, are now resurging as the intense heat subsides. Since early August, when extreme heat swept the country, the number of mosquitoes captured noticeably dropped, but recently, the numbers have been increasing again.

According to the status of digitally collected mosquitoes (DMS) in Seoul on September 7, the number of mosquitoes caught at 55 locations throughout the city on September 4 reached 1,978—the highest one-day figure in about a month since August 2, when 2,064 were captured. The mosquito index announced by the Korea Disease Control and Prevention Agency (KDCA) for seven regions nationwide also soared to 100.9, nearly double the previous week’s figure of 53. In fact, an analysis of mosquito counts collected by Seoul’s DMS over the past five years shows that the average number of mosquitoes in September was 67,535, which is 8.4% higher than August’s average of 62,114.

A mosquito is hanging on a leaf. Photo by Yonhap News Agency

The main reason mosquitoes become more prevalent in the fall than in the summer is the extreme heatwaves seen in recent years. Mosquitoes are most active when the temperature is around 25 to 30 degrees Celsius. If the temperature rises too high, however, their lifespan is cut in half and their activity declines sharply. As cold-blooded animals, mosquitoes find it difficult to survive at temperatures above 35 degrees Celsius.

This summer as well, daytime highs surpassed 40 degrees Celsius, triggering heatwave warnings, and drought conditions caused breeding puddles to dry up, destroying the habitat. However, with heavy rains comparable to autumn monsoons falling after mid-August, and cooler mornings and evenings setting in, the optimal environment for mosquito breeding has returned.

As the heatwave subsides and cool breezes begin to blow in the mornings and evenings, mosquitoes are becoming rampant. On the 8th, officials from Paldal-gu Public Health Center are conducting pest control at a park in Ingye-dong, Paldal-gu, Suwon City, Gyeonggi Province. Yonhap News

In particular, fall mosquitoes are known to be much fiercer and itchier than summer mosquitoes. Experts explain, "Fall is the spawning season for mosquitoes, so they are much more aggressive in biting hosts to obtain the energy needed to lay eggs." At this time, they also secrete higher concentrations of hirudin—an anticoagulant protein—which keeps the bitten area itchy for much longer. Additionally, due to the impact of climate change, the mosquito activity season is extending further into late autumn.

Experts add, "During the fall, mosquitoes tend to invade indoors, seeking out warm environments," and advise, "To prevent mosquito bites, carefully seal drainage holes at the bottoms of window frames and block entry routes into the home." They also recommend, "When going out, avoid dark-colored clothing that attracts mosquitoes, wear long sleeves and long pants, and remember that the effectiveness of mosquito repellent diminishes with sweat, so it should be reapplied every three to four hours for safety."

An image for better understanding of the article, unrelated to specific content. Shutterstock

Meanwhile, pet dogs are also at risk of contracting heartworm disease if bitten by mosquitoes, so owners must exercise extra caution on walks. According to veterinary science, heartworm typically parasitizes the right ventricle and right atrium of the heart, and early infection usually shows no symptoms. However, as the disease progresses, weight loss, lethargy, ascites, heart failure, and even shock may develop, with severe cases leading to death.

It should be noted that heartworm cannot be transmitted directly from an infected dog to other dogs through contact; transmission only occurs through mosquitoes. To prevent this, preventive medication should be administered regularly—once a month—not only during the active mosquito seasons of summer and early fall, but also year-round. If the medicine is skipped for two or three months and then resumed, it is essential to first test at an animal hospital for heartworm infection before administering the medication to ensure safety.

This content was produced with the assistance of AI translation services.