Forensic entomologists rely on laboratory growth data to estimate the time of blow fly colonization on human remains. Several data sets exist for the development of the common blow fly Lucilia sericata (Meigen) (Diptera: Calliphoridae), and although they generally describe similar rates of preadult development, all vary. Such differences could be explained by genetic variation, environmental (rearing) variation, or both. In the study presented here, flies from a single population were reared under variable conditions of food moisture, substrate type, substrate freshness, and sampling, to determine the effect each had on developmental time. Cohorts were tested in a single incubator at a single temperature and humidity, to eliminate effects of undesired environmental variation. Fly developmental times were significantly influenced by multiple laboratory rearing treatments; food moisture, transferring postfeeding larvae to fresh substrate, and destructive sampling affected different stages of development. Developmental times ranged from 329 to 505.5 h, covering the spectrum of variation observed in published data sets. Growth was then compared with larval development on rat carcasses under the same environmental conditions, establishing a link between laboratory-controlled growth and development on carrion. Cohorts raised on rats matured to adulthood between 333 and 337 h, which was best mimicked by the fastest growth treatment observed under laboratory conditions. The large environmental influence on development observed in this study could affect forensic entomology casework and accentuates the need for a standardized means of rearing flies in a laboratory setting that is relevant to decomposition on a corpse.