The most widespread mosquito on the Galápagos Islands appears to have developed a taste for reptile blood. Biologists fear that the newly discovered behavior may leave many of the islands' rare reptiles at risk for mosquito-borne diseases, such as West Nile virus, that they haven't adapted to cope with.

A study published online today in the Proceedings of the National Academy of Sciences USA reports that the black salt marsh mosquito (Aedes taeniorhynchus), which feeds on birds and mammals and is common along the coasts of North and South America, is now also feasting on the blood of marine iguanas and Galápagos tortoises.

Rather than arriving with humans in recent years—like the other two mosquito species on the Galápagos—the A. taeniorhynchus seems to have been on the islands for about 200,000 years, according to the new study. This stretch of time would have given the species a chance to adapt to the novel environment—which was dominated by reptiles before the arrival of humans—where it also breeds at higher and drier conditions than its continental counterparts.

"The genetic differences of the Galápagos mosquitoes from their mainland relatives are as large as those between different species," Arnaud Bataille, a graduate researcher at the University of Leeds and lead study author, said in a statement, "suggesting that the mosquito in Galápagos may be in the process of evolving into a new species."

Sampling of blood-full black salt marsh mosquitoes from 18 sites across the archipelago's islands revealed that 58 percent of the insects had been slurping reptile blood. Only one of the 105 meals sampled came from a bird—a surprising figure because birds were more common than reptiles in some sampled areas, "suggesting that reptile blood may have become a preferential choice for this mosquito," the authors wrote.

The researchers recommend keeping a better eye on mosquito populations to look out for new pathogens, as well as stringent spraying standards for planes and boats. "With tourism growing so rapidly the chance of a disease-carrying mosquito hitching a ride from the mainland on a plane is also increasing," study co-author Andrew Cunningham, a wildlife epidemiologist at the Zoological Society of London, said in the statement.

Image of a tortoise in the Galapagos courtesy of Marilyn Cruz/Galapagos National Park