For instance, although there are thousands of species of mosquitoes, only those of the genus Anopheles transmit malaria​—the world’s second-deadliest communicable disease (after tuberculosis).

Still, other mosquitoes transmit a host of different maladies. WHO reports: “Of all disease-transmitting insects, the mosquito is the greatest menace, spreading malaria, dengue and yellow fever, which together are responsible for several million deaths and hundreds of millions of cases every year.” At least 40 percent of earth’s population are at risk for malaria, and about 40 percent for dengue. In many places, a person can contract both.

But warmer weather can do more. In some areas it transforms rivers into puddles, while in others it triggers rains and floods that leave behind stagnant pools. In both cases the standing water serves as a perfect breeding ground for mosquitoes. Hotter weather also shortens the mosquitoes’ breeding cycle, speeding up their reproduction rate, and it lengthens the season during which mosquitoes abound. In warmer weather, mosquitoes are more active. Hotter temperatures even reach inside the mosquito’s gut and intensify the reproduction rate of disease-causing microbes, thereby increasing the likelihood that a single bite will cause infection.