The larvae and prepupae of the black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae) have been explored as a means for alternate protein production for feed for animals that are raised for human food. However, processes for production of these and other insects must be refined if cultivation is to become widespread and efficient. In this study, black soldier fly larvae were fed one of six diets, consisting of the Gainesville house fly diet (control), and five diets of varying ratios of sorghum and cowpea. Effects on life-history traits and nutritional content of prepupae were observed. Flies were able to successfully complete larval development on all diets tested. There were significant differences in development rates based on diet, particularly the diets containing a higher percentage of sorghum. In general, larvae reared on the sorghum diets (which were lower in protein than that of the cowpea diets), developed slower (3-9 days longer from larval eclosion to the prepupal stage) than those on the cowpea diets. Diet treatment did not consistently influence weight or length of prepupae. Higher protein diets (7.73% protein) translated to higher protein content of prepupae (43.70-47.29% protein) and lower protein diets (3.51% protein) resulted in greater gross energy content of prepupae (5.22-6.21 Kcal/g). These differences suggest that macro-nutrient content of prepupae can be influenced by larval diet. This study provides further evidence of the viability of black soldier flies for protein production.