NPR has a story about why urinal manufacturers chose the fly as a target to reduce splashing.
Keiboom in Amsterdam says the original fly idea was proposed almost 20 years ago by Dutch maintenance man Jos Van Bedoff, who had served in the Dutch army in the 1960s. As a soldier he noticed that someone had put small, discrete red dots in the barracks urinals, which dramatically cut back on "misdirected flow."
Two decades later, he proposed to the airport board of directors that the dots be turned into etched flies. According to Keiboom, Van Bedoff decided that guys want to directly aim at an animal they can immobilize. The ability to use one's natural gifts and achieve victory over the foe while standing is the key, he explained. Guys, he felt, can always beat flies. That's why flies are so satisfying.
Is that the answer?
Berenbaum, the entomologist, says she's not convinced. More than a hundred years ago in Britain, bathroom bowls also sported insect images, she says. Back then, however, the favored target was not a fly, but a bee. And bees have stingers. It seems that men in the 1890s were willing to take more imaginative risks when peeing.