Dr. Gaden, Dr. Wagner and others say that pheromones could alleviate some of the reliance on poison. “We’re trying to move away from brute-force techniques like pesticides and achieve the most environmentally friendly control of lampreys possible,” Dr. Wagner said.

Researchers have been investigating lamprey pheromones since the 1980s, though records from the late 19th century show that French fishers suspected that lampreys use odor to attract mates. In fact, pheromones seem to play a prominent role throughout the lamprey life cycle.

Like salmon, lampreys spawn in rivers and streams, but instead of returning to the place of their birth, they use the scent of current larvae — which burrow into the muck and remain there around four years before metamorphosing into parasites and moving into open water — to determine where to deposit their own young. “It’s like choosing where to raise your kids based on a neighborhood’s crime rate and quality of schools,” Dr. Wagner said. “The odor larvae release says, ‘We’re thriving here.’”

Male lampreys follow their noses to larvae-filled streams ahead of females. There, they construct a cradle of small stones (the name lamprey possibly derives from the Latin lampetra, or “stone licker”) and then pump out a concoction of come-hither chemicals to guide females to their love nests. After spawning, both parents die.

Making larvae is not the only way the parasites use scent, however. Researchers also suspect that lamprey tissue contains an alarm cue, which warns others to steer clear of injured or dead lampreys. When Dr. Wagner pours just a few drops of a solution extracted from decaying lampreys into a tank of live ones, their frenzied response makes it appear as if someone just flipped on a blender.

The researchers hope to use synthesized versions of these three chemical classes to hack lampreys’ natural behaviors, creating a “push-pull” means of control, with the alarm pheromone nudging the animals away from certain areas, the migration and sex ones reeling them in. Lamprey males could be tricked into selecting subpar streams, females could be sent down dead ends, and all could be manipulated for more cost-effective poisoning and trapping. Such pheromone-driven strategies have long been used for insects, but never for a vertebrate species.