Not all species of flies are safe and effective as medicinal maggots. There are thousands of species of flies, each with its own habits and life cycle.
Those flies whose larvae feed on dead animals will sometimes lay their eggs on the dead parts (necrotic or gangrenous tissue) of living animals. When maggots are infesting live animals, that condition is called "myiasis." Some of those maggots will feed only on dead tissue, some only on live tissue, and some on live or dead tissue. The flies used most often for the purpose of maggot therapy are "blow flies" (Calliphoridae); and the species used most commonly is Phaenicia (=Lucilia) sericata, the green blow fly. Monarch Labs' Medical Maggots™ are a specific strain of P. sericata that was tested for safety and efficacy over the course of 12 years.