Given the techniques available to chemists at the end of the nineteenth century and the beginning of the twentieth, the mysterious substances remained elusive. Then, in the 1930s, a persistent German chemist at the Kaiser Wilhelm Institute for Biochemistry in Germany decided to tackle the problem.

Adolph Butenandt had already made a name for himself by discovering the human sex hormones estrone, testosterone, and progesterone. Branching out into a different arena, he aimed to discover the substance that female moths use to attract males. Butenandt thought the work would open up an entirely new field of research, and like Lintner, he envisioned this research creating a new way to control insect pests.

Butenandt pursued his goal throughout the years of Hitler’s regime, World War II, and Germany’s long recovery after the war. The task was difficult. He began by snipping off the abdominal tips of virgin female silkworm moths and grinding them up. Then, using analytical chemistry techniques, he separated the moth slurry into various extracts and tested each one on male silkworm moths. The domesticated silkworm moth has lost its ability to fly. But the male will flutter his wings when excited by a nearby female—and when fooled by one of Butenandt’s extracts.

Working over the course of nearly three decades, Butenandt ground up about half a million female silkworm moths in his quest to identify their alluring perfume. At last in 1959, he announced success: The substance was a kind of alcohol that Butenandt christened bombykol, after the moth’s Latin name, Bombyx mori.

That same year German biochemist Peter Karlson and Swiss entomologist Martin Lüscher introduced the term “pheromone” (Greek for “carrier of excitement”). The researchers were working on identifying the chemicals that maintain the elaborate caste system of termites, and they coined the word to describe a substance that an animal gives off to trigger a specific behavioral or developmental reaction in another member of the same species.

Butenandt’s successful characterization of an insect pheromone inspired others to undertake the tedious effort required to seek out the pheromones made by other insects.

Behavioral assays, such as the wing-fluttering response used by Butenandt, remained key to identification of pheromones throughout the 1960s. For example, in 1961, Colin G. Butler at the Rothamsted Experimental Station in London used a behavioral assay to identify a pheromone that regulates the physiological development of an insect, specifically the honey bee. Scientists knew that queen bees emit a substance that stops worker bees from rearing other queens. Butler tested mandibular gland secretions to determine whether they inhibited worker bees from constructing specialized queen rearing chambers. Through this behavioral assay he identified a pheromone produced by the queen bee that would not only suppress the rearing of queens, but also halt the development of the worker bees’ ovaries.

Scientists quickly turned their attention from studying beneficial insects, such as the silk moth and the honey bee, to investigating pestiferous insects. Using behavioral assays, researchers identified the pheromones used as attractants by the black carpet beetle, the California 5-spined engraver beetle, the western pine beetle, the cabbage looper moth, and a leaf-cutting ant, among others.

Many scientists were frustrated in their search for pheromones. Further progress would depend on the development of new methods and approaches. Was there, for example, another more general test for pheromones?

Researchers had been pondering the question for some time. As early as 1953, Peter Karlson had suggested to his neighbor, biologist Dietrich Schneider, that he use his expertise in electrophysiology to develop an electrical means of detecting pheromones.

Schneider took up the challenge. At the time biologists suspected that the large furry antennae of many moth species enabled them to detect pheromone molecules in the air. Schneider came up with the brilliant idea that he could use the antennae as “sniffers” for pheromones, reasoning that they might respond to a relevant chemical with a small burst of electrical activity, a characteristic response of nerve cells when stimulated.

Schneider removed an antenna from a male silk moth, bathed it in a saline solution to keep its cells fresh, and lodged it between two electrodes, devices that sense electrical activity. He then gave the antenna a whiff of air that swept past an extract containing bombykol (graciously provided by Butenandt’s lab). The biologist was thrilled to note a peak of electrical activity in the antenna corresponding to exposure to the extract. Schneider named this odor-prompted electrical response of an insect antenna an “electroantennogram” (EAG). He reported his technique in 1957.