Ruspolia differens Serville (Orthoptera: Tettigoniidae) is an insect with significant economic potential in Africa. However, to mass-rear this species on a large scale, the optimal rearing temperature needs to be determined. We assessed multiple performance traits for R. differens reared at seven constant temperatures, ranging from 18 to 32°C, from newly hatched nymphs to 3 wk after adult molting. The highest observed survival was at 30°C (mean survival of 86.7%), where also the development rate reached its maximum. At this temperature, the development from newly hatched nymphs to adults took approximately 49 d. The weight of individuals at the time of adult molt reached its maximum at 28°C (mean weight of 0.62 g). To maximize the yield from mass-rearing, suggested time to harvest R. differens is 10 d after the adult molt. According to our results, during this time period R. differens individuals can achieve up to 50% higher weight than if harvested immediately after adult molting. For maximal survival and weight gain, we recommend rearing temperature of 28–30°C, whereas a slightly higher temperature of 31°C leads to the shortest development time. Taking into account all the performance traits, the overall optimal temperature is estimated at 29°C. Our results can be used when developing large-scale, mass-rearing protocols for R. differens in controlled temperatures.