More Mosquito Days? That Sucks!
On the Eastern Shore, half the year is prime mosquito time.
Mosquitoes thrive in warm, humid weather. We have plenty of that here. And as the global climate warms, many places will become more hospitable to mosquitoes. The Eastern Shore is one of those places.
The Big Picture:
According to Climate Central, a nonprofit climate science research organization, a mosquito day is any day that has both
- an average relative humidity of 42% or higher and
- daily minimum and maximum temperatures from 50–95°F
Salisbury, Md. had 180 mosquito days in 2022.
Climate Central calculated mosquito days for 242 locations across the country for each year between 1979 and 2022 and concluded that “as the U.S. has warmed over the last 43 years, the annual number of mosquito days has increased in many places.” Of the 242 locations studied, 173 (71%) saw annual mosquito days increase, by an average of 16 days a year.
Salisbury saw an increase of 16 mosquito days per year in that time period.
Some locations showed a decrease in the number of mosquito days. Many of those are in the South, where summer temperatures frequently exceed the range that is mosquito friendly.
As spring and fall temperatures warm, mosquitoes emerge earlier and survive later. Salisbury has added eight warm days in the spring and seven in the fall. The mosquitoes love it!
By the Numbers:
Of the nine major climate regions in the country, six have over 100 mosquito days per year.
The Southeast region is the leader, averaging 218 mosquito days each year; the South is not far behind. Although Maryland is in the Northeast region, the Eastern Shore has more than the average number of mosquito days in that region.
Why is this Important?
Mosquitoes are annoying, to be sure, but they also spread diseases.
There are about 50 species of mosquitoes in Maryland and Delaware. The three most common are Aedes aegypti (yellow fever mosquito), Aedes albopictus (Asian tiger mosquito), and Culex pipiens (common house mosquito).
These three species spread West Nile virus, Dengue fever, Yellow fever, Chikungunya, Zika virus, several forms of encephalitis, and more.
These diseases are arboviruses, that is, viruses spread to people through the bite of infected insects such as mosquitoes or ticks. Of these diseases, only West Nile virus has been reported in Delmarva counties.
The CDC and state health departments monitor arboviruses through ArboNET, a national surveillance system. ArboNET collects data on arboviral infections among people, veterinary animals, mosquitoes, dead birds, and sentinel animals (animals used to detect risks to humans by providing advance warning of a danger, like canaries in coal mines).
The CDC has published the cumulative number of cases of West Nile virus reported through ArboNET for the period 1999-2022. In that period nationally, there were 56,569 human disease cases, 25,769 hospitalizations, and 2,773 deaths. The number of cases per Eastern Shore county is shown in the chart below.
The Bottom Line:
Although relatively small so far, there is a real public health threat from a longer mosquito season on the Shore. But as Axios noted recently, “Mosquitoes — and the diseases they sometimes carry — are shaping up as one more climate change-induced problem for many local officials to worry about.”
Jan Plotczyk spent 25 years as a survey and education statistician with the federal government, at the Census Bureau and the National Center for Education Statistics. She retired to Rock Hall.
Common Sense for the Eastern Shore
