As if climate change wasn’t already bad enough, we now have one more reason to change course. Summer heat is hanging around longer, the days are becoming more humid, and mosquito season is lengthening, which means an increased risk of vector-borne diseases like Zika.

Baltimore tops the list of growing mosquito seasons, according to an analysis by Climate Central. Since 1980, the metro area has seen a 37-day increase in the season of bug bites, which now lasts 152 days on average. In Washington, the season has lengthened by 29 days to 143.

Why is this happening? As temperatures slowly increase across the United States, the number of days above 50 degrees grows. And as things get warmer, more moisture is evaporated into the air which increases the humidity. Mosquitoes love hot and humid days.

Climate Central analyzed temperature and humidity trends for the largest cities in the United States, specifically within the preferred range of the Asian tiger mosquito — 50 to 95 degrees, with a relative humidity of at least 42 percent. The Southeast tends to be the most habitable for the bloodsuckers, and more than 20 U.S. cities have ideal conditions for at least 200 days of the year.

But 10 cities have seen these conditions extend by more than a month, as far north as Minneapolis and Portland, Maine.

1. Baltimore (37 days)
2. Durham, N.C. (37 days)
3. Minneapolis (34 days)
4. Myrtle Beach, S.C. (34 days)
5. Raleigh (33 days)
6. Portland, Maine (32 days)
7. St. Louis (31 days)
8. Pittsburgh (30 days)
9. Worcester, Mass. (30 days)
10. Albany, N.Y. (30 days)

This is a worrying trend given new prevalence of Zika, a mosquito-borne illness that was once limited to South America and the Caribbean but has since spread through travel to the United States. Zika causes mild symptoms in a majority of the population, but can cause severe birth defects in newborn babies if the mother happens to contract the illness.

On Wednesday, Morning Mix reported, the Florida Department of Health added two more patients to their list of possibly non-travel-related Zika cases, bringing the total number of cases to four. This means mosquitoes in the United States are likely infected with the disease and have the ability to spread it.

The Florida Health Department is taking this development very seriously, going door-to-door, urging locals and visitors to cooperate and collecting urine samples within a 150-yard radius of each person with the illness, Reuters reported.

Of course, it’s not just Zika to be concerned about. West Nile virus, dengue, chikungunya and Rift Valley fever all have a presence in the United States. In 2012, cases of West Nile set a record when 5,674 people were diagnosed with the illness. Nearly 300 of those patients died.

Climate Central sums up its findings:

  • Cities like Baltimore and Durham, N.C., have seen their annual average mosquito season grow by nearly 40 days since the 1980s.
  • Dozens of cities across the Midwest, Northeast, and along the Atlantic Coast have all seen their mosquito seasons grow by at least 20 days over the past 35 years.
  • More than 20 major U.S. cities have ideal climate conditions for mosquitoes at least 200 days each year.
  • In a few hot Southern cities, rising extreme heat since the 1980s has actually caused the mosquito season to begin to decrease (though there are still hundreds of days each year with ideal conditions for mosquitoes in these locations).