The secondary screwworm, Cochliomyia macellaria (Fabricius), was reared on either equine gluteus muscle or porcine loin muscle at 20.8°C, 24.3°C, and 28.2°C. C. macellaria needed ≈35% more time to complete development when reared at 20.8 than 28.2°C. Furthermore, larval growth and weight over time did not differ between larvae reared on equine versus porcine muscle. This study is the second in the United States to examine the development of C. macellaria and is the first to examine development of this species on muscle tissue from different vertebrate species. These data could provide significant information regarding time of colonization, including myiasis and neglect cases involving humans and animals. Furthermore, these results in comparison with the only other data set available for this species in North America indicate a fair amount of phenotypic variability as it relates to geographic location, suggesting caution should be taken when applying these data to forensic cases outside the region where this study was conducted.