The abdomen distends when the fly is engorged with food. At the posterior end, the female has a segmented ovipositor which can be retracted and extended to facilitate egg laying.
The ovipositor has sensory structures which help the female select suitable oviposition sites.
The male has posterior genitalia which are mostly withdrawn when the fly is not mating.
During mating the complex lobes of the male genitalia clasp the ovipositor of the female and sperm are injected into the female. The sperm move to a storage area (spermatheca) in the female reproductive system and remain available to fertilize eggs as they pass down the oviduct. A female can therefore lay several batches of fertilized eggs after only one successful copulation.
Female house flies are monogamous, i.e., they normally mate only once.
A volatile sex pheromone, muscalure, (Z)–9–tricosene, is produced by the female and attracts males.
In the mating process, the male sometimes grasps the female in the air, but actual copulation takes place while resting on a surface, rather than in flight.
The female mates and begins laying eggs 3–4 days after emergence (preoviposition period). The threshold for preovipositional development is about 14°C (57°F).
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