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The name of William D. McElroy may not resonate today, but for kids growing up in Baltimore in the 1940s through the 1960s, he was one of the world’s leading experts in bioluminescence who paid them for the lightning bugs they had netted on their nightly summer sortees across yards and fields.

McElroy discovered that the insect’s flash was the result of an enzymatic reaction with the compound ATP, or adenosine, and was used in mating.

To encourage his youthful hunters at the first gathering that was held in 1947, McElroy offered a bounty of 25 cents for every 100 fireflies that were delivered to his office in Mergenthaler Hall on the Johns Hopkins University Homewood campus

He also offered a $10 prize to the most successful gatherer. At the conclusion of the first “season,” which ended in mid-August, the honor went to Morgan Buchner Jr., 10, of Hadley Square.

In average years, youthful Baltimoreans in pursuit of the little blinking harbingers of summer could collect at least 500,000 specimens. By the 1960s, they were netting 1 million a year.

Reacting to criticism that the firefly population was being depleted, McElroy explained the children were collecting only males, as the females remain in the grass, where they lay their eggs.

McElroy, who earned the sobriquet of the “firefly man,” said in a 1977 interview, “Quite frankly, that was the most fun I ever had in my life.”