Particle feeding in Aphodius dung beetles (Scarabaeidae): old hypotheses and new experimental evidence

Abstract

Abstract1. Published studies of the highly specialized mouthparts of adult scarabaeid dung beetles have proposed that the beetles feed on (1) liquid with minute particles, squeezed out of the dung by the mandibular molars, and/or (2) dung particles that are finely ground by the same molars. These hypotheses were tested experimentally.2. The maximum size of ingested particles was determined in six Aphodius species (Scarabaeidae, Aphodiinae) feeding on dung with latex‐balls of known diameters. The probability of ingestion decreased with particle size. The diameter of balls with a 5% chance of ingestion varied between species from <5 µm to about 25 µm. This maximum size, which precludes hypothesis (1), was related to feeding habits, not to body mass.3. Simple experiments did not indicate any comminution by the mouthparts of dung particles.4. It is suggested that coarse (mostly indigestible) particles are rejected by filtering setae and that the remaining small particles, prior to ingestion, are concentrated on the molars by squeezing which eliminates superfluous water.5. Since 40–50% of the dry matter in fresh dung from grazing cows, sheep and horses consisted of particles <20 µm, food competition among adult Aphodius seems unlikely in spite of their selective feeding.