 In 1999, Robert Robbins, then chair of the Department of Entomology at the Smithsonian Institution’s National Museum of Natural History, stated that "Glassberg’s butterfly guides have provided a new way for amateur naturalists to identify species without collecting them or dissecting them.Previously, he said, butterfly books distinguished between species using technical, almost microscopic details.But in Mr. Glassberg’s years of field observation, Dr. Robbins said, he has found variations in the way butterflies appear that allow species – or the sex of individuals of a species – to be distinguished simply by looking.