Twin Cities' mosquito season has increased by 2 weeks in last 4 decades

MINNEAPOLIS -- A 43-year-old study by Climate Central on mosquito weather trends has found that out of 242 testing locations in the U.S., 173 of those locations saw an annual mosquito day increase by 16 days on average. 

Hot and humid weather is the perfect catalyst for a boom in mosquito populations. When spring weather warms earlier than usual, and temperatures stay warm throughout the fall, mosquitoes can emerge earlier and survive longer. 

However, temperature is only one factor that could influence an influx of annual mosquito days. Humidity, rainfall, and drought have all been linked to years that saw an increase in mosquito days. 

For analysis sake, a mosquito day is considered a day where the average relative humidity is 42% or higher, and the daily minimum and maximum temperatures are between 50-95 degrees Fahrenheit. 

In 55 locations, annual mosquito days increased by 21 days or more.   

Regions in the U.S. that experience the most mosquito days each year, on average, are the Southeast, South, and the Ohio Valley. The current annual average amount of mosquito days for the Southeast is 218 days (60% of the year). In the South it's 184 days (or 50% of the year), and in the Ohio Valley it's 146 days (or 40% of the year). 

Locations that saw the biggest increase in mosquito days since 1979 were in California (Santa Maria, San Francisco, Salinas), Pennsylvania, Washington State, New Hampshire, Alabama, Vermont, West Virginia. 

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There are more than 200 species of mosquitos in the U.S. Most of them are harmless, albeit annoying. 

However, about a dozen species in the U.S. can spread viruses and parasites to people; most commonly West Nile virus, dengue, and Zika. Additionally, there are much fewer cases of mosquito-borne diseases compared to other insect-borne diseases in the U.S., most of which are carried by ticks. 

West Nile was reported in numerous counties across Minnesota in 2022, including counties within the metro (Hennepin and Washington), counties as far north as Cass and Koochiching, as far west as Clay, Wilkin, Traverse, Stevens, and Rock county, and as far east as Fillmore county. 

RELATED: Anoka County expected to have more mosquitos than any other metro county

To learn more about the potential risk for increased mosquito days in your area, click here.