The black soldier fly, Hermetia illucens L., was reared on a grain-based diet at 27, 30, and 36°C. Survival of 4- to 6-d-old larvae to adults averaged 74–97% at 27 and 30°C but was only 0.1% at 36°C. Flies required a mean of ≈4 d (11%) longer to complete larval and pupal development at 27°C than at 30°C. At 27 and 30°C, females weighed an average of 17–19% more than males but required an average of 0.6–0.8 d (3.0–4.3%) longer to complete larval development. At both temperatures, adult females lived an average of ≈3.5 d less than adult males. The duration of larval development was a significant predictor of adult longevity. Temperature differences of even 3°C produce significant fitness tradeoffs for males and females, influencing life history attributes and having practical applications for forensic entomology.