Mosquito Season Is Here, and This Summer Risk Is Easy to Ignore Until It Isn’t
Matt Bachus
Midwestern roots planted firmly in Colorado soil—that's where my real estate approach begins...
Midwestern roots planted firmly in Colorado soil—that's where my real estate approach begins...
Experts warn of a brutal mosquito season ahead in Colorado
A mild winter and warmer temperatures are setting the stage for an intense mosquito season in Colorado, with increased activity predicted by experts.
DENVER — Jefferson County has confirmed Colorado's first human case of West Nile virus for 2026, and a Colorado State University insect expert is warning residents that this mosquito season could be worse than previous years.
Karim Gharbi, a horticulture specialist with CSU Extension whose background is in insects, said the mild winter has set the stage for a surge in mosquito activity across the state.
"I would expect to see more bites," Gharbi said. "Definitely, we are going to see more insect activity in general."
Gharbi said he expects the next four to five months to be difficult in certain areas, with the season potentially stretching from June through October if temperatures remain warm into the fall.
"I mean, I definitely say it's going to be a worse year than in previous years," he said. "I can't say it's going to be the worst year on record for mosquitoes."
Why dry winter made things worse
Gharbi explained that a colder, wetter winter would have naturally thinned the mosquito population.
"A wetter winter may have us kill off more insects," he said. "If it's wetter and colder, it causes the eggs to freeze, the crystals pierce their bodies, and they die."
Without those conditions, more mosquitoes survived into the warmer months.
Urban areas are particularly vulnerable, Gharbi said, because cities and neighborhoods create ideal breeding environments.
"Around urban areas, that's where a lot of these mosquitoes thrive because we create the conditions they love, and there are no predators," he said.
Coloradans who spend time outdoors — running, hiking, or walking — are especially at risk, Gharbi said, because physical activity makes people more attractive to mosquitoes.
"The more CO2 and heat you are releasing, the more attractive you are," he said.
West Nile virus threat
Jefferson County Public Health confirmed the state's first human West Nile virus case of the year on June 2. The virus spreads through the bite of an infected mosquito. Most people who contract it do not feel sick, but some experience fever, headache, body aches or fatigue. In rare cases, the illness can become serious.
People 60 and older and those with compromised immune systems face a higher risk of severe illness, according to Jefferson County Public Health.
Last year, 286 Coloradans were infected with West Nile virus, and 18 died, according to the Colorado Department of Public Health and Environment.
Gharbi said the warming trend is extending the window during which the virus can spread.
"We are going to see potentially more transmission and a longer transmission window for West Nile virus, and maybe other mosquito-borne illnesses," he said.
He noted that mosquitoes in alpine areas are not typically West Nile vectors, but those in urban areas and wetlands can be. Hikers at higher elevations may see some relief, as fewer pools of standing water exist there to support mosquito populations.
How to protect yourself
Gharbi said eliminating standing water around the home is the most effective prevention step. Garden trays, overturned pots, gutters, buckets, and birdbaths can all become breeding grounds.
"To prevent mosquitoes from being an issue, we should eliminate any standing water," he said.
He also noted that dark-colored clothing is a prime attractant for mosquitoes and other biting flies, such as deer flies and horse flies — though he emphasized that skin pigment is not a factor.
"This does not apply to skin pigment," Gharbi said. "They are not more attracted to people with darker skin."
Jefferson County Environmental Health Director James Rada echoed the need for vigilance despite the dry conditions.
"Dry weather doesn't mean mosquitoes aren't around," he said.
Despite the grim outlook for this summer, Gharbi said he remains hopeful about the long-term fight against mosquito-borne illness.
"I do think that it is possible with the current rate of research that we can be free of mosquito-borne illnesses in our lifetime," he said.
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