Mosquitoes are nature’s opportunists. They will eat anything from plant nectar to blood from chickens, rats, alligators, frogs—and, of course, humans. And now a new study finds that when humans encroach on wild places, these insects may develop a special taste for human blood above all other food sources.
Researchers in Brazil analyzed blood samples from mosquitoes collected in nature reserves in the Atlantic Forest, a heavily deforested region of Brazil. Several of the collected species showed “a clear preference for feeding on humans,” said Jeronimo Alencar, a biologist at the Oswaldo Cruz Institute in Brazil and an author of the paper, in a statement.
The findings jibe with previous evidence that deforestation brings humans in more contact with creatures that spread deadly diseases. Mosquitoes can transmit Zika, dengue fever, malaria and encephalitis, to name a few illnesses—all of which are harmful to human health and can kill.
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The findings were published on Thursday in Frontiers in Ecology and Evolution.
According to the researchers, the Atlantic Forest supports about 270 mammalian species, 850 kinds of birds and about 570 reptiles and amphibians. The forest once spanned 1.3 million square kilometers across Brazil—an area larger than Texas and California combined. But it has been reduced to less than a third of that size by agricultural and residential development.
The study has several limitations. For one, it only analyzed blood from 145 female mosquitoes, and not all these samples could be identified, so it’s unclear how broadly the results can be applied. It’s also unclear how mosquitoes’ preferences have changed since the Atlantic Forest was fully intact.
Still, the study could help researchers better understand the complex relationship between deforestation and disease. Humans eliminate about 10 million hectares of forest per year. “Deforestation reduces local biodiversity, causing mosquitoes, including vectors of pathogenic agents, to disperse and seek alternative food sources,” the authors write. And those sources, it turns out, may be us.