Below the antennae projects the proboscis or “mouthparts”.
The proboscis is readily extended and retracted. Projecting from the basal portion of the proboscis is the pair of maxillary palps.
At the end of the proboscis is a fleshy bilobed structure (labellum) or “oral sucker” with extensive ridges (pseudotrachea) which are food channels leading to the mouth opening. The fleshy labellum is pressed against any food.
The pseudotracheae on each labellum are oriented towards the opening to the food channel (mouth) and are kept dilated by chitinous rings which determine the size of food particles that can be ingested (0.0003–0.004 mm diameter).
Some larger particles may get ingested directly into the food channel without passing through the pseudotracheae.
The fly can ingest food material just by sucking up liquid foods. Alternatively, it uses the prostomal teeth to scrape the food surface, and then moistens it with regurgitated saliva and liquid vomit, so that a liquefied material can be ingested.
Regurgitation while feeding leaves light-coloured spots which, along with dark faecal spots, causes soiling of surfaces.
The mouthparts of the house fly are called sponging-sucking due to the fleshy structure and method of liquefying foods before ingestion. Muscular action of the pharynx is used to take up the food by suction.
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