Knowledge of the feeding habits of aquatic insects and assignation to different functional feeding groups contributes to a better comprehension of aquatic ecosystems. The feeding habits of larval stages (4–6 mm) of Cloeon dipterum (Linnaeus, 1761) were studied through mouthpart morphology, gut content and were tested in food particle size preference experiments. The description of the mouthparts consisted in the dissection of them and their observation in an optical microscope. Gut content analysis was carried out by ventral dissection of the thorax to isolate the digestive tract. The content of each larva was homogenized, mounted on slides and observed under an optical microscope at 400× magnification with a graduated eyepiece. Food preference experiments consisted on offering fine particulate organic matter (FPOM) and coarse (CPOM) leaves of Laurus nobilis simultaneously. Mouthparts are characterized by robust mandibles with well-developed and asymmetric molar surfaces and maxillae and labium with developed palps, with short setae. Gut content of C. dipterum was dominated by fine detritus represented by 76.9% (SD = 25.7) of the covered area. Also, in the food preference experiments was detected that FPOM consumption was greater than CPOM. Consequently, we consider that the larval stages of C. dipterum are functionally classified as collectors-gatherers preferring fine particle size, and secondary scrapers for CPOM manipulation.