This therapy was used in the 16th century but its popularity declined with the takeover of antibiotics and new surgical methods for treating wounds. Maggots eat the bacterial micro-organisms present in wounds. This arrests bacterial infection.
Maggots also secrete a substance that serves as an antibacterial weapon against bacterial infection.
A third benefit of MDT is that the maggots produce a potent brew of enzymes to decompose dead wound tissue. The maggots then eat this decomposition. The skin is then clean and free to grow and heal. Actually these worms eat only the dead tissue. The worms secrete ammonia and calcium carbonate which actually encourages recovery of the wound.