Cochliomyia macellaria, commonly known as the secondary screwworm, is a species of blow fly found primarily in the Americas. It is recognized for its role in decomposing organic matter and can be a pest in livestock, as its larvae may infest wounds and cause significant harm to animals. The adult flies are typically metallic blue or green and measure about 10-14 mm in length. Cochliomyia macellaria is attracted to decaying flesh and can be found in areas with abundant organic material, making it an important species in forensic entomology for estimating the time of death in criminal investigations.