US regions are experiencing longer mosquito seasons due to climate change
As the climate warms, many places are becoming more hospitable to mosquitoes, according to a new analysis from Climate Central.
Climate Central assessed mosquito weather trends from 1979 to 2022 covering nine major regions in 242 locations across the United States to calculate the annual number of mosquito days in each region. 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 and 95 degrees Fahrenheit.
Mosquitoes thrive in warm, humid conditions and pose a variety of health risks.
The analysis found that 173 sites, or 71% of the 242 analyzed, saw annual mosquito days increase by an average of 16 days. In 55 localities, the annual mosquito days increased by 21 days or more.
The 10 places that have seen the biggest increase in mosquito days
Based on data from 1979 to 2022, these 10 locations have seen the greatest increase in mosquito days:
- Santa Maria, California – 43 days
- San Francisco, California – 42 days
- State College, Pennsylvania – 33 days
- Seattle-Tacoma, Washington – 32 days
- Manchester, NH – 31 days
- Birmingham, Alabama area – 30 days
- Burlington, Vermont – 29 days
- Clarksburg-Weston, West Virginia – 28 days
- Salinas, California – 28 days
- Wheeling, West Virginia – 28 days
Regions with more than 100 mosquito days each year
Based on the average annual number of mosquito days from 1979 to 2022, these regions experience the most mosquito days each year:
- South East: 41 localities with an annual average of 218 mosquito days each year, i.e. 60% of the year
- South: 41 localities with an annual average of 184 mosquito days each year, i.e. 50% of the year
- Ohio Valley: 46 localities with an annual average of 146 mosquito days each year, i.e. 40% of the year
- West: 16 localities with an annual average of 132 mosquito days each year, i.e. 36% of the year
- Northeast: 34 localities with an annual average of 129 mosquito days each year, i.e. 35% of the year
- Upper Midwest: 23 localities with an annual average of 112 mosquito days each year, i.e. 31% of the year
Have the mosquito days decreased somewhere?
The southeast and south experience mosquito days for more than half the year, the highest in the country; however, many places where summer temperatures frequently exceed mosquito-friendly conditions are experiencing a decrease.
61 locations, mostly in the south, saw fewer long-term mosquito days.
The most common mosquito-borne diseases in the United States
Of the more than 200 species of mosquitoes found in the continental United States, about a dozen are known to spread viruses and parasites to humans, which means they are often just harmless, annoying parasites. There are relatively few cases of mosquito-borne diseases compared to other insect-borne diseases in the United States, most of which are transmitted by ticks, and infection rates and severity of health effects which result are much lower compared to tropical and subtropical regions. .
The most common of these species are Culex, a carrier of West Nile virus, and Aedes, which can transmit chikungunya, dengue, and Zika viruses.
Although dengue — once known as “fractured fever” for the severe muscle and joint pain it can cause — is not currently common in most of the United States, with the exception of Florida and Puerto Rico, continued warming will put tens of millions more people in the United States and Canada at risk of Aedes-virus transmitted by 2050, according to projections. Some cases of dengue can result in a rare hemorrhagic form which can be fatal.
West Nile virus is the most common mosquito-borne disease in the United States and is spread by several Culex mosquito species, which have widespread suitable habitats, as well as ticks.
Compared to tick-borne Lyme disease, cases of West Nile virus are more prevalent, especially in the plains and central United States. In a tiny percentage of cases, it causes inflammation in the brain that can take weeks or months to recover and sometimes causes permanent effects, according to the Centers for Disease Control and Prevention.
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