Hoverflies (Syrphidae) play a key role in pollination services across ecosystems but are underrepresented in pesticide toxicity research. Laboratory toxicity testing is a fundamental step toward evaluating pesticide risks, yet established protocols for hoverflies are lacking. This study aims to fill this gap by developing an acute oral toxicity test for Eristalinus aeneus, a cosmopolitan hoverfly. A novel oral toxicity test was introduced using a custom-designed test cage with artificial flowers, allowing precise measurement of food consumption and dose assessment. Both individual and group feeding setups were tested, with group feeding proving more feasible, overcoming key limitations of individual feeding, including difficulty in locating food and evaporation of liquid diets. As an additional validation step, an oral toxicity test was conducted with dimethoate — a reference insecticide commonly used in toxicological studies — using three concentrations (0.007, 0.0014, and 0.0007 g/L). The estimated LC₅₀ values for E. aeneus were ~0.00166 g/L (24 h) and ~0.00137 g/L (48 h), with corresponding LD₅₀ values of ~0.56 and ~0.46 μg/g fly. Our results indicate that E. aeneus is highly sensitive to dimethoate and slightly more sensitive than Apis mellifera. These findings underscore the need to include E. aeneus and other syrphids in future toxicity testing and highlight the value of the developed methodology for ecotoxicological studies and conservation efforts.