Mosquito bites are to be expected in the warm summer months, but increasingly these pests are hanging around into autumn. In addition to extending the time we’re vulnerable to itchy, annoying bites, a longer mosquito season also extends the risk period for serious mosquito-borne illnesses.
The United States now regularly documents cases of West Nile virus, along with rarer infections like eastern equine encephalitis (EEE) and dengue fever. Florida, in particular, is facing one of its worst dengue surges in decades. Just in the last week, one person died from the infection, per AP News.
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“The end of summer does not necessarily mean the end of mosquito risk,” says Nirbhay Kumar, PhD, a professor of global health at the George Washington University Milken Institute School of Public Health in Washington, DC.
Epidemiologists and entomologists (aka bug scientists) say several factors are driving the lengthening of mosquito season, including changing weather patterns. And, they say, this increase comes with very real health risks and the need for prevention strategies.
Why Mosquito Season Is Getting Longer and More Intense
Multiple elements are allowing the mosquito population to thrive. “Temperature is a major driver,” says Mark Janko, PhD, an assistant professor of epidemiology and environmental health at the University at Buffalo in New York. Mosquitoes belong to a category of animals known as “ectotherms,” meaning they rely on external sources to maintain their body temperature, Dr. Janko says. “Warmer temperatures can extend the portion of the year when they are active, particularly when autumn stays warm, and the first hard freeze comes later,” he explains.
Most insects are active when temperatures are above 50 degrees F, according to Elmer W. Gray, an entomologist and public health extension specialist at the University of Georgia in Athens. “The more days we have over this temperature, the more opportunity there is for insect populations to flourish,” he says.
Nighttime temperatures can be particularly impactful, according to Gray. “The warmer it stays at night, the less cooling impact there is on the larval habitats, and the more generations of mosquitoes that can be produced over the course of the year,” he says.
But those higher temperatures don’t just increase mosquito populations; they also allow germs to thrive. “Temperature also affects how quickly some mosquito-borne pathogens — viruses and parasites — develop inside mosquitoes, potentially increasing the period during which mosquitoes remain infectious and can transmit disease,” Dr. Kumar says.
Rainfall may contribute, although its relationship to mosquito populations is “complicated,” according to Janko. “Wet periods can create [a] breeding habitat, while drought can sometimes concentrate mosquitoes, wildlife, and people around remaining water sources,” he says. “Climate change is therefore altering not only the length of mosquito season, but when and where conditions are favorable for different mosquito species.”
All of these factors impact regions across the United States differently. “In northern and temperate areas, warmer spring and fall temperatures can lengthen what was historically a fairly seasonal period of mosquito activity,” Janko says. “In warmer parts of the South and West, the issue may be less about creating a new ‘mosquito season’ and more about extending activity further into the year or changing which mosquito species can thrive locally.”
