Why do swimming pools have a lot of gadfly?

Have you ever noticed that there are often many blood-sucking insects (such as horseflies, mosquitoes, etc.) flying around to bite you after a bath or before a summer thunderstorm, or when you’re at a suburban swimming pool? Is your blood particularly fragrant? Not really. It turns out that there’s a substance in human blood that attracts blood-sucking insects. Some people have isolated this substance from human blood and found that it attracts many flies and mosquitoes when released into the air. Even when diluted 2000 times, its attractiveness to flies and mosquitoes is still five times greater than that of water. Recent studies by scientists have shown that this attractive blood substance is produced by a mixture of various amino acids with a strong sweetness. This attractiveness is also related to external temperature and humidity. On hot days or after swimming, when the body temperature rises and blood vessels expand due to vigorous exercise, this attractive substance quickly permeates the skin and spreads out.

When swimming, due to vigorous exercise, body temperature rises, and blood vessels expand. Moreover, the high population density in swimming pools enhances the effect of this attractive substance. According to entomologists’ multiple studies, horseflies especially love water sources, which further increases the number of horseflies in swimming pools.