NEW YORK—A new bee is buzzing in Brooklyn: The tiny insect, the size of a sesame seed, sips the sweet nectar of the city—sweat.

"They use humans as a salt lick," said entomologist John Ascher, who netted the first known specimen of the species in 2010 while strolling in Brooklyn's Prospect Park near his home. "They land on your arm and lap up the sweat."

North...