おそらくPIE*pleuのハエが語源で、語源的にはハエと同じ。
"A man named 'Mueller' put on the first trained-flea circus in America at the old Stone and Austin museum in Boston nearly forty years ago. Another German named 'Auvershleg' had the first traveling flea circus in this country thirty years ago. In addition to fairs and museums, I get as high as $25 for a private exhibition." ["Professor" William Heckler, quoted in "Popular Mechanics," February 1928. Printed at the top of his programs were "Every action is visible to the naked eye" and "No danger of desertion."]