Jun 22, 2023 - Energy & Environment

"Mosquito days" are getting more common nearly nationwide

Change in annual days hospitable for mosquitoes, 1979 to 2022
Data: Climate Central; Chart: Axios Visuals

The number of "mosquito days" — that is, those with the hot and humid weather the flying insects crave — has increased in many U.S. cities over the past several decades, per a new analysis.

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

Why it matters: Mosquitoes are more than just a nuisance — they're a public health threat, carrying diseases such as malaria, West Nile, Zika and more.

Driving the news: 71% of the 242 locations Climate Central analyzed saw an increase in mosquito days between 1979 and 2022, of about 16 days on average.

Zoom in: Santa Maria, California; San Francisco and State College, Pennsylvania, saw the greatest increases in mosquito days during that time frame, at 43 days, 42 days and 33 days, respectively.

Data: Climate Central; Chart: Axios Visuals

Yes, but: Some locations — particularly in the South — are actually getting too hot for mosquitoes, the analysis notes.

  • They don't thrive in temperatures above 95° F — an increasingly common reading in southern summers.
  • The ongoing Texas heat wave has heat indices reaching upward of 120° F across parts of the Lone Star State, Axios' Andrew Freedman reports.
  • The number of mosquito days in Austin, for example, is notably trending downward:
Data: Climate Central; Chart: Axios Visuals

Of note: Other factors, such as rainfall and drought, can also influence mosquito activity.

  • They breed in pools of standing water, common after major storms.

What's next: Experimental efforts to control mosquito populations by releasing genetically modified versions of the insects into the wild are underway in Florida and elsewhere.

  • Those projects, however, are controversial among some locals and skeptics who view them as tampering with the natural ecosystem.

The bottom line: Mosquitoes — and the diseases they sometimes carry — are shaping up as one more climate change-induced problem for many local officials to worry about.

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