Jul 6, 2023 - News

Denver's mosquito season is shrinking — but this summer will bring swarms

Data: Climate Central; Chart: Axios Visuals
Data: Climate Central; Chart: Axios Visuals

Mosquitoes in Denver are getting mixed reviews this year.

What's happening: New data shows the city's mosquito season has shrunk, bucking a national trend spurred by climate change. But recent record rainfall across Colorado is cooking up an extra "spicy mosquito stew" this summer that we'll all have to contend with, experts tell us.

Driving the news: "Mosquito days" — that is, days with the hot and humid weather the flying insects crave — have trended downward in Denver over the past several decades, per a new analysis, Axios' Alex Fitzpatrick and Kavya Beheraj write.

  • The report, from nonprofit climate science research organization Climate Central, defines a "mosquito day" as one with an average relative humidity of 42% or higher, plus daily temperatures of 50° to 95°.

By the numbers: Denver had 39 of those days in 2022, compared with 50 in 1979, according to Climate Central's analysis.

  • The 11-day decrease could reflect long-term drought conditions across the region because mosquitoes need moisture to thrive, says biology professor Bob Hancock, who studies the insects at the Metropolitan State University of Denver.

Yes, but: This summer, be prepared for mosquito mayhem.

What they're saying: "We are not only breeding crazy numbers of mosquitoes here in Colorado with our rainy year, but we are keeping the ones that we're breeding alive very well because it's not getting as hot as it usually does," Hancock, who's known as the Mosquito Man, tells us.

What we're watching: Whether wet conditions across most of the state will translate into a bad West Nile year. Last week, a pool of mosquitoes in Boulder County tested positive for the virus.

Flashback: The state recorded the highest number of West Nile cases in the country last year, with 132 people developing severe neurological problems and 20 related deaths — more than in any year since 2003.

Be smart: Health experts say the best way to avoid mosquitoes is to cover exposed skin while outdoors — particularly at dusk and dawn; drain any standing water, which is where the insects lay their eggs; and wear insect repellent with DEET, Picaridin or lemon eucalyptus oil.

Go deeper: Think you're sweet? Mosquitoes don't.


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