Adult drone flies (Syrphidae: Eristalis spp.) resemble male honeybees in appearance. Their immature stages are commonly known as rat-tailed maggots due to the presence of a very long anal segment and a telescopic breathing tube. The larvae are associated with decaying organic material in liquid or semi-liquid media, as in the case of other saprophagous eristalines. Biological and morphological data were obtained from both laboratory cultures and sampling in the field. Drone flies are important pollinators for wild flowers and crops. In fact, mass rearing protocols of Eristalis species are being developed to be used as efficient alternative pollinators. However, deeper knowledge of larval morphology and biology is required to improve artificial rearing. The production quality control of artificial rearing must manage the consistency and reliability of the production output avoiding, for example contamination with similar species. This article presents the first description of the larva and puparium of E. similis, including a comparative morphological study of preimaginal stages of the anthropophilic and ubiquitous European hoverfly species E. tenax. Scanning electron microscopy has been used for the first time to describe larvae and puparia of both species. Moreover, the preimaginal morphology of E. similis has been compared with all known descriptions of the genus Eristalis. The main diagnostic characters of the preimaginal stages of E. similis are the morphology of the anterior spiracles (shape of clear area and arrangement of facets) and pupal spiracles (length, shape, and arrangement of tubercles). Microsc. Res. Tech., 2013. © 2013 Wiley Periodicals, Inc.