Lucilia sericata, the green bottle blowfly, has a long history of clinical use and an excellent safety record which makes it safe for therapeutic clinical use. In regions where it is naturally absent, maggot therapy cannot be offered to patients with chronic wounds unless an alternative local species is found. This chapter explains how new species are identified and tested for their therapeutic efficacy and clinical safety. The process involves the bioprospecting for candidate fly species, pre-clinical in vitro and animal studies to make sure they are therapeutically active and safe, and clinical trials of maggot therapy with human patients.