Charles Darwin spent eight years studying barnacles. His research ran broadly from 1846 to 1854 and covered both living and fossil forms of these small marine crustaceans.
The project began after Darwin had already returned from the voyage of HMS Beagle and published important work in geology and natural history. He initially examined barnacles to improve his expertise in classification, but the investigation expanded into a comprehensive study of their anatomy, development, variation, and relationships. He collected specimens, dissected them, and compared examples from many locations.
Darwin published the results in detailed monographs on living and fossil Cirripedia. The work established him as a leading authority on barnacles and earned him the Royal Society's Royal Medal in 1853. It also gave him valuable evidence for thinking about how related organisms could differ and how apparently unusual forms might fit into evolutionary relationships.
The barnacle years are often treated as an odd detour before Darwin published his theory, but they were scientifically important preparation. By the time he finished, he had developed greater confidence in taxonomy and anatomy. Darwin later joked about his intense involvement with the subject, famously writing that he hated barnacles more than anyone could.