Disease-spreading mosquitoes are rapidly multiplying in the US—and surprisingly it doesn't appear to have anything to do with climate change. Mosquito populations in New York, New Jersey, and California have increased as much as tenfold in the past 50 years, and the number of mosquitoes in those places has as much as quadrupled, according to a press release. "These increases are correlated with the decay in residual environmental DDT concentrations and growing human populations, but not with temperature," researchers state in a study published Tuesday in Nature Communications. It's a conclusion that may catch those who assumed climate change was the biggest mosquito-booster off guard.
The agricultural use of DDT was banned in the US in 1972, NBC News reports, but researchers were shocked to discover how long it was lingering in the environment. The dangerous insecticide could still be found in some New York soil samples as recently as 2000. Regardless, as it continues to dissipate, mosquito populations are rebounding. Meanwhile, growing cities are drawing some of the most dangerous mosquitoes—those that spread West Nile and dengue, among other diseases—that prefer to live around buildings while driving out more benign species that prefer wetlands and forests. According to UPI, mosquitoes that like to bite humans tend to like cities, which are chock full of humans. (These are the 10 worst US cities for mosquitoes.)