Adult rhinoceros beetles use a sweeping pattern to ingest high-viscosity fluid

More than half of all insect species utilize various natural liquids as primary diet. The concentrated liquids with energy-dense nutrition can provide highly favorable rewards, however, their high-viscosity poses challenges to the insect for ingesting. Here we show that rhinoceros beetles, Trypoxylus dichotomus (Coleoptera: Scarabaeidae), are capable of ingesting sugar solutions with viscosities spanning four orders of magnitude, exhibiting extraordinary adaptability to diverse natural liquid sources. We discovered a previously unidentified maxillae-sweeping motion that beetles preferentially adopt to consume highly viscous liquids, achieving a higher feeding rate than the more common direct sucking. By utilizing morphological characterizations, flow visualization, and fluid–structure coupling simulation, we revealed the underlying mechanisms of how this maxillary movement facilitates the transportation of viscous liquid. Our findings not only shed light on the multi-functionality of beetle mouthparts but also provide insights into the adaptability of generalized mouthparts to a broad range of fluid sources.