Flies, like many insects, lack the muscular, mobile tongue found in mammals, leading to confusion about how they eat. They are equipped with a highly specialized external feeding organ instead of a fleshy tongue. This unique structure allows them to process and consume nutrients, despite only being able to ingest liquids.
The Fly’s Equivalent of a Tongue
Flies eat using a sophisticated mouthpart called the proboscis. This flexible, elongated structure functions as a feeding tube and is an extension of the fly’s lower lip, or labium. The proboscis is designed for a sponging or lapping mechanism, meaning the fly cannot bite or chew solid food. Therefore, all consumed nutrients must be in a liquid or semi-liquid state before ingestion.
Anatomy of the Proboscis
The proboscis is divided into three sections: the rostrum, the haustellum, and the terminal labellum. The labellum consists of two fleshy pads that make contact with the food source. Its inner surface is covered in numerous tiny channels called pseudotracheae. These pseudotracheae act as microscopic capillary tubes, drawing liquid food inward by capillary action. The channels converge at the central oral opening, or prestomum, which leads to the fly’s main food canal. This structure allows the fly to efficiently soak up fluids from a surface, much like a sponge.
How Flies Consume Their Meals
Flies are liquid feeders and must liquefy any solid food before ingestion. When a fly encounters a solid source, it first regurgitates a mixture of saliva and digestive fluids onto the material. These enzymes begin to dissolve the solid nutrients externally. Once the food breaks down into a liquid slurry, the fly extends its proboscis and presses the labellum onto the droplet. The pseudotracheae then draw the liquid meal up into the food canal, transporting it into the fly’s stomach or a storage pouch called the crop.
Where Flies Keep Their Taste Buds
Flies possess chemoreceptors, the insect equivalent of taste buds, on their mouthparts and other body parts. The labellum of the proboscis is equipped with these sensory structures, allowing the fly to confirm the suitability of a food source before ingestion. A significant number of taste receptors are also located on the fly’s feet, or tarsi. This distribution means a fly can “taste” a potential meal simply by walking across its surface. If the receptors detect attractive compounds, such as sugars, it triggers a reflex to extend the proboscis and begin feeding.