The invention of the microscope in the seventeenth century revealed a miniature world no less vast and complicated than the depths of the starry heavens, themselves gloriously unveiled not long before by the telescope. Creatures previously invisible to human eyes proved to be crafted in detail as marvelous as that of any visible plant or beast, a fact that threw religion and science (in those days still known as natural philosophy) into an existential confusion, from which neither discipline has yet emerged entirely. It was one thing to discover new continents or new constellations, and quite another to discover, as Antonie van Leeuwenhoek—the Dutch inventor of the microscope—did with some horror, that whole kingdoms of “animalcules” were carrying on their lives within his own mouth. One of the chief confusions presented by these tiny creatures was their place in the ranks of animal and vegetable. In 1705, when the erudite Swede Olof Rudbeck Junior published his biblical study The Selah Bird: Neither Bird nor Locust, his readers were still as likely as the ancient Hebrews to see bugs and birds as essentially similar creatures.
more from the NYRB here.