Maggot Life Cycle

There are thousands of varieties of flies, all of which produce eggs and larvae, otherwise known as maggots. However, maggots are not created equal. Some maggots like to feed on healthy tissue as well as necrotic tissue. This is not a good thing for medical debridement.

One of the most common flies is the green blowfly, Phaenicia [Lucilia] sericata. The green blowfly is the only fly approved to produce medical maggots in the United States. This fly's larvae feed only on necrotic tissue and avoid healthy tissue. They are ideally suited for maggot debridement therapy (MDT).The word "blowfly" comes from the term "to blow," meaning the depositing of eggs. This species has been used to produce maggots successfully for decades and is also provided by labs in Wales, Australia, and Israel.

Blowflies lay their eggs on necrotic tissue, carrion and feces, upon which the larvae then feed. Blowflies are usually the first scavengers on the scene after a death, and forensic scientists can make estimates of the time of death based on the maggot activity they find in a corpse.

R.A. Sherman

A female blowfly can lay up to 2000 or 3000 cream-colored eggs in a few weeks time, depositing them in various places. Depending on the fly species and the environmental temperature, larvae hatch within 8 to 24 hours. The eggs hatch into small larvae that look like small translucent grains of rice. The larvae are about 1 to 2 mm in length at 1 day. The maggots release proteolytic enzymes into their surrounding environment, and this allows them to consume the semi-liquid material. They enlarge as they take nutrition, swelling to 1 cm in length by the 3rd or 4th day.

After feeding for 4 to 7 days, the maggots leave the wound or corpse to pupate in the ground. Seven to 20 days later, an adult fly emerges from the pupa. Within 1 or 2 weeks, the adult fly reaches reproductive maturity and the cycle starts all over again. It's obviously important to remove the larvae from the wound before they begin the process to form pupae, thus treatments are usually limited to 48 to 72 hours.

Additionally, larvae prefer warm dry areas to pupate, so they will attempt to leave the moist wound when it's time for them to pupate. Although blowflies frequently lay their eggs on dead animals, they may also deposit eggs on infected or gangrenous wounds of live animals, such as cattle or humans. It's this propensity that brought them to the attention of physicians in the first place. Maggots cannot be disinfected, so the eggs are chemically disinfected with Lysol, sodium hypochlorite, or another agent. The eggs are placed in sterile containers so that the newly hatched maggots remain disinfected.

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Treatments with larvae (maggots) is limited to 48 to 72 hours, so they are removed from the wound before they begin to migrate to form pupae.

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