The common house fly, Musca domestica, is a familiar insect. It undergoes complete metamorphosis, a process involving four distinct stages: egg, larva, pupa, and adult. The entire process, from a fertilized egg to an adult fly, can take as little as seven to ten days under ideal warm conditions.
From Egg to Larva
The life cycle of a house fly begins when a female lays tiny, white, oval-shaped eggs, each about 1.2 mm long. A single female can lay up to 150 eggs at a time, often in batches. These eggs are typically deposited in moist, decaying organic matter such as garbage, compost piles, or animal waste, providing an immediate food source for the hatching larvae. The eggs hatch quickly, usually within 8 to 24 hours, depending on environmental conditions like temperature.
Once hatched, the larvae, commonly known as maggots, are legless, creamy-white, worm-like creatures, ranging from 3 to 12 mm in length, with a narrower head end and a blunt rear end. This larval stage is a period of rapid growth, as maggots consume the decaying organic matter around them. They molt their skin several times as they increase in size. This stage usually lasts about 3 to 5 days, but can extend depending on the temperature and food availability.
The Pupal Transformation
After the larval stage, the maggot prepares for its next transformation by seeking a drier location, sometimes burrowing into soil or hiding under objects. The larva’s skin then darkens and hardens, forming a protective, barrel-shaped casing known as the puparium. This casing can vary in color from yellowish-red to dark brown or black as it ages.
Inside this immobile pupal case, the maggot undergoes internal reorganization. During this period, which lasts approximately 3 to 6 days under warm conditions, the larval tissues break down and reorganize to form the complex structures of the adult fly, including wings, legs, and other adult features. The pupa does not feed during this transformative stage.
Emergence of the Adult Fly
Once metamorphosis within the pupal case is complete, the adult fly is ready to emerge. It uses a fluid-filled sac on its head, called a ptilinum, which inflates and deflates like a pneumatic hammer, to push open the pupal case.
Upon emergence, the adult fly is often soft and pale, with its wings still crumpled. Within a few hours, its wings expand and its exoskeleton hardens and darkens. The fly’s primary actions immediately following emergence include seeking food sources to gain energy and preparing for reproduction.
Continuing the Cycle
The adult house fly, typically grayish with four dark stripes on its thorax, lives for about 15 to 30 days, though this can vary based on temperature and food availability. Adult flies are active, searching for food and suitable places to lay eggs. They feed on various liquid or semi-liquid substances, often liquefying solid materials with their saliva.
A female house fly is capable of reproducing within just a few days of emerging from the pupa. While a female may mate only once, storing sperm for future use, she can lay multiple batches of eggs throughout her lifespan. Each batch can contain 75 to 150 eggs, and over her lifetime, a single female can produce hundreds of eggs, potentially up to 500 or even 900. This rapid reproductive capacity ensures the continuation of the fly’s life cycle.