A description of the larval development of Wohlfahrtia magnifica (Schiner, 1862) is given. An interpretation of the morphological development correlated with functional and adaptive aspects of myiasis-causing flies is also included. A detailed analysis of morphological changes that occurred in W. magnifica larvae during postembryonic development is carried out. These changes happen in 2 larval interinstars, I-II and II-III, in which several structures such as anterior and posterior peritremes and cephalopharyngeal skeleton play an important role. The possible functions of these structures are considered. We also describe the first instar in W. magnifica to differentiate it from that belonging to Sarcophaga species, paying special attention to disposition of the cephalopharyngeal skeleton, anterior peritremes, and spinulation on the last 3 segments. Several structures, not described previously in Sarcophagidae, were observed: modified spines of the buccal and peritremal cavities, peritremal tubercles, and modified spines on the ventral surface. Changes occurring in these structures during larval development are described. Their probable role in the taxonomy of the genus Wohlfahrtia and their application to Nearctic species belonging to this genus, Wohlfahrtia vigil and Wohlfahrtia opaca, are also discussed.