We compared the larval morphology of the genera Ataenius and Aphodius. The third larval instars of five Ataenius species: Ataenius opatrinus Harold, A. picinus Harold, A. platenis (Blanchard), A. simulator Harold and A. strigicauda Bates, are described or redescribed and illustrated. The most important morphological characteristics of the larvae of Ataenius are found in the respiratory plate of thoracic spiracle, the setation of venter of the last abdominal segment, the setation of the epicranial region and the morphology of the epipharynx. A key to larvae of the known species of Ataenius is included.
The larval morphology of Aphodius (Plagiogonus) nanus Fairmaire, 1860 and A. (P.) arenarius (Olivier, 1789) are described and redescribed, respectively. The common characters of both species, and the specific diagnostic characters are provided and discussed. The most important morphological characters of the larvae of Plagiogonus Mulsant, 1842 are the longitudinal alignment of the anterior setae of the stipes, the spatulate form of the posterior-lateral setae of the glossae of the hypopharynx, the slight development of the anal lobe slit, the form of the epitorma of the epipharynx, the slight sclerotization of the pternotormae and the relative length of second antennal segment. A key to the larvae of both species of Plagiogonus is presented along with life history data and the preferred food of these species. This study shows that A. arenarius and A. nanus feeding habits are closer to saprophagy than to coprophagy.