Michael Tessler realized his life had taken an odd turn. His days were spent not in an office, not out with friends — but alone in the woods, attracting leeches.

Sometimes, they were so bountiful that “it was like the forest floor was moving toward me,” he recalled. “Even for someone who’s used to having swarms of leeches coming at me, it could be intimidating to see that many of them.”

Dr. Tessler, a postdoctoral fellow at the American Museum of Natural History’s Sackler Institute of Comparative Genomics, subjected himself to this horror movie scenario for the good of science. He collected hundreds of leeches and analyzed their last blood meals, hoping to identify their animal victims — and thus to reveal the range of species living in the forest.

Copious leech bites later, Dr. Tessler’s sacrifice paid off. He was a co-author on two papers confirming that leeches and their blood meals offer a fast, cheap method for surveying biodiversity. Such basic data can be surprisingly difficult to come by, yet is often critical for making conservation decisions.