Will Mosquito Season Ever End?

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 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.”

Infections Spread by Mosquitoes Are on the Rise

How Mosquitoes Threaten Your Health

Bites can be uncomfortable, leading to intense itching. “A mosquito bite causing a localized itchy, red, or swollen reaction is a result of varying sensitivity of people to chemicals in the mosquito saliva,” Kumar says. “Scratching makes the itching worse by irritating the skin and promoting inflammation.”

Scratching a mosquito bite can also break the skin barrier, allowing germs to enter the body more easily and increasing the risk of disease, Kumar notes.

• Fever
• Aches and pains
• Nausea
• Rash

Although uncommon, these infections can become neuroinvasive, meaning impacting the brain. Warning signs of neuroinvasive disease include:

• Disorientation
• Seizures
• Neck stiffness

People who work outdoors, children, older adults, and those who are immune compromised are at the highest risk for severe complications from mosquito-borne illnesses, Gray says. “However, as COVID-19 taught us, everyone reacts differently to viruses.”

How to Protect Yourself Against Mosquitoes Late Into the Season

Personal protection and home yard management are important to protect against mosquitoes at this point in the year, according to Gray.

Cover Your Skin and Use Mosquito Repellent

“Skin that is not covered should be treated with an EPA [Environmental Protection Agency]-approved repellent when exposed to mosquito populations,” he says.

Gray notes that, in addition to DEET, there are several botanically based, EPA-approved options, including oil of lemon eucalyptus and catmint oil, that are effective at preventing mosquito bites.

“If you'll be exposed to significant populations or have been warned about possible disease transmission threats, then higher concentrations of DEET, IR3535, or picaridin may be in order,” Gray says. He also suggests wearing light-colored, loose-fitting pants and long-sleeved shirts to reduce the amount of exposed skin that mosquitoes could bite.

Get Rid of Standing Water Outside, or Treat It

To lower the risk of mosquitoes gathering around your property, Gray recommends eliminating standing water and treating water that can’t be removed with an EPA-approved larvicide to kill immature stages of mosquitoes. “If your town or county has an organized mosquito control program, communicate with them and support their efforts,” Gray says. “Mosquito control today is a highly technical and scientifically based profession.”