Flies – Detail

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Life Cycle

All flies undergo complete metamorphosis with egg, larva, pupa, and adult stages in their development.

The female fly deposits her eggs in animal waste or moist organic material where the larvae, or “maggots,” complete their development, feeding on bacteria associated with their developmental site.

When the maggots have completed their development and are ready to undergo the next step in their metamorphosis, they convert their last larval skin into a puparium, a hardened shell within which the pupa develops.

Within the puparium, the pupa transforms into an adult fly, which pops off the end of the puparium and emerges. Body fluids pump into the fly’s veins, causing the wings to unfold and expand and allowing them to dry and harden so that the adult can fly.

The rate of fly development is dependent upon temperature, and under optimal summertime conditions flies may develop from egg to adult in as little as 7 days. Once the female fly has mated, she can lay several batches of eggs, typically containing over 100 eggs each.

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Common fly categories found in Hong Kong
  • House fly (Musca Domestica)
  • Face fly (Musca autumnalis)
  • Stable fly (Stomoxys calcitrans)
  • Little house fly (Fannia canicularis)
  • Garbage fly (especially in the genus Phaenicia)
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Communicable diseases

Myiasis

Myiasis is the invasion of living tissue or organs of vertebrates by larvae of fly (maggot). Feeding activity of the larvae may cause serious tissue damage, often accompanied by putrid discharge and ulceration, resulting in loss of function, injury to the skin, secondary bacterial invasion and death.

Chrysomya bezziana

Chrysomya bezziana, the Old World Screw-worm Fly, is an obligate parasite of mammals. The site of infection is usually at superficial wounds. Adult fly feeds on decomposing corpses, decaying matter, excreta and flowers. Adult female only lays eggs on live mammals, depositing approximately 200 eggs at sites of wounding or in body orifices such as the ear and nose. Wounds in the size of a tick bite are sufficient to attract egg-laying.

The eggs hatch in 24 hours and the resulting larvae burrow into the host’s tissues and feed on the host’s dead or living tissue. The larvae are unable to develop in carrion. They leave the wound after 5-7 days and fall to the ground to pupate. Under hot and humid weather, they can complete the life cycle within 15-30 days. Adult flies live on average for 2-3 weeks.

Chrysomya bezziana is an agent of myiasis: the infestation of live vertebrate animals with larvae, which, at least for a certain period, feed on the host’s dead or living tissue. Feeding activity of the larvae may cause serious tissue damage, resulting in loss of condition, injury to the skin/hide, secondary invasion and death. Same as other members of this genus, Chrysomya bezziana adults commonly visit faeces and decaying matters. Because of this habit, they, therefore, are mechanical carriers of pathogens.