To ensure the effective conservation of biodiversity the distribution of species needs to be accurately characterized and areas of high species richness located. For many taxa this can be achieved only by experienced taxonomists. Taxonomic research has a large input from non-professional or amateur researchers, in addition to professionals working at museums or universities. The decline of taxonomy and the number of taxonomists within the professional community has been widely publicized, but the trends in the activities of amateur taxonomists are unclear. Because amateurs contribute many valuable records of species occurrence this may have a disproportionate impact upon the information available for conservation planning and represents an underappreciated threat to conservation planning. We use taxonomic research by UK entomologists in order to evaluate the changing role of both amateur and professional taxonomists. We reviewed contributions by British-based authors to Entomologist's Monthly Magazine over the past century. Our results show that both amateur and professional taxonomy have undergone a long and persistent decline since the 1950s, in terms of both the number of contributors and the number of papers contributed. It is argued that the conservation community needs to help try and reverse the decline of taxonomy.