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.