Sponging Type of Mouth Parts (e.g. Housefly)
The prominent fleshy and retractile proboscis consists mainly of the labium and is attacked in elbow – like form to the elongated head. The proboscis can be differentiated into basal rostrum and distal haustellum. The proboscis is grooved on its anterior surface, within this groove lie the labrum-epipharynx (enclosing the food canal) and slender hypopharynx (containing the salivary canal). Mandibles are absent. The maxillae have evidently become fused with the fleshy elbow of proboscis, and only the prominent single segmented maxillary palpi remains.
The end of the proboscis is enlarged, sponge like and two-lobed which acts as suction pads. They are called labella. The surfaces of labella are transverse by capillary canals called pseudotracheae, which collect the liquid food and convey it to the food canal. These insects often spit enzyme-containing saliva onto solid foods to liquefy them and then sponge up the mixture.
Feeding Mechanism: When labella are pressed against the exposed liquid material, the pseudotracheae absorb it and get filled with by capillary attraction. The liquid is then collected at a point on the labella wherein these tiny channels converge. From this point the liquid is then drawn up through food channel formed in-between the two stylets viz. labrum epipharynx and hypopharynx.