As the climate warms, many places are becoming more hospitable to mosquitoes, a new Climate Central analysis found.
Climate Central assessed mosquito weather trends from 1979 to 2022 spanning nine major regions in 242 locations across the United States to calculate the annual number of mosquito days in each area. The analysis, which saw increases in many locations, defines “mosquito days” as having an average relative humidity of 42% or higher and daily minimum and maximum temperatures between 50 to 95 degrees Fahrenheit.
Mosquitos thrive in warm and humid conditions and come with a variety of health risks.
The analysis found that 173 locations, or 71% of the 242 analyzed, saw annual mosquito days increase by 16 days on average. In 55 locations, annual mosquito days increased by 21 days or more.
The 10 locations that saw the biggest increase in mosquito days
Based on data from 1979 to 2022, these 10 locations saw the biggest increase in mosquito days:
- Santa Maria, Calif. – 43 days
- San Francisco, Calif. – 42 days
- State College, Pa. – 33 days
- Seattle-Tacoma, Wash. – 32 days
- Manchester, N.H. – 31 days
- Birmingham Area, Ala. – 30 days
- Burlington, Vt. – 29 days
- Clarksburg-Weston, W.Va. – 28 days
- Salinas, Calif. – 28 days
- Wheeling, W.Va. – 28 days
Regions with over 100 mosquito days each year
Based on the average annual mosquito days from 1979-2022, these regions experience the most mosquito days each year:
- Southeast: 41 locations with an average annual of 218 mosquito days each year, or 60% of the year
- South: 41 locations with an average annual of 184 mosquito days each year, or 50% of the year
- Ohio Valley: 46 locations with an average annual of 146 mosquito days each year, or 40% of the year
- West: 16 locations with an average annual of 132 mosquito days each year, or 36% of the year
- Northeast: 34 locations with an average annual of 129 mosquito days each year, or 35% of the year
- Upper Midwest: 23 locations with an average annual of 112 mosquito days each year, or 31% of the year
Have mosquito days decreased anywhere?
The Southeast and South experience mosquito days for more than half of the year, the highest in the nation; however, many locations where summer temperatures frequently exceed suitable mosquito conditions are seeing a decrease.
61 locations, mostly in the South, saw fewer mosquito days over the long-term.
Most common mosquito-borne diseases in the U.S.
Of the more than 200 mosquito species found in the continental U.S, about a dozen are known to spread viruses and parasites to people, which means they’re more often just harmless, annoying pests. There are relatively few cases of mosquito-borne diseases compared to other insect-borne diseases in the U.S., most of which are carried by ticks, and rates of infection and the severity of resulting health effects are much lower when compared to tropical and subtropical regions.
The most common of these species are Culex, a West Nile virus carrier, and Aedes, which can transmit chikungunya, dengue, and Zika viruses.
Although dengue — once known as “breakbone fever” for the severe muscle and joint pain it can cause — is not currently common in most of the U.S., with the exception of Florida and Puerto Rico, continued warming will put tens of millions more people in the U.S. and Canada at risk from Aedes-transmitted viruses by 2050, according to projections. Some cases of dengue fever can result in a rare hemorrhagic form that can kill.
West Nile virus is the most common mosquito-borne disease in the U.S. and is spread by several Culex mosquito species, which have widespread suitable habitats, as well as ticks.
Compared to tick-borne Lyme disease, West Nile virus cases are more widespread, especially in the Plains and Central U.S. In a tiny percentage of cases it causes brain inflammation that can take weeks or months to recover from and sometimes causes permanent effects, according to the Centers for Disease Control and Prevention.
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