The Importance of Morphology in Further Unraveling the Bumblebee Flight Paradox

The size of a bumblebee relative to its wing span would suggest that flight is not possible according to the conventional aerodynamic theories, yet nature shows that not to be true, hence the bumblebee paradox. Bumblebee wings have venations that create corrugations, with their forewing and hindwing connected with a hook-like structure, known as a hamulus. Previous investigations of bumblebee flight modeled wings as smooth surfaces or neglected their accurate morphological representation of corrugation or used a simplified body. To address these shortcomings, this work explores the significance of vein corrugation and body on lift and thrust, and morphological importance of hindwing and forewing in flapping flight. Computational fluid dynamics simulations were used to analyze an anatomically accurate bee wing and body for hovering and forward speeds. Flow analysis of corrugated and smooth wing models revealed that corrugation significantly enhanced lift by 14%. With increasing speed, the hindwing increased lift from 14% to 38% due to the combined camber created by the forewing and hindwing. A notable feature was that the leading edge vortex did not change in size when the hindwing was removed, therefore forewing pressure remained the same as when coupled with hindwing during downstroke. When the bee body was included in the model, the pressure decreased locally between the wing root to 25% of the wingspan on the dorsal side, causing lift for the corrugated model to increase by 11%. The study demonstrates the importance of accurately modeling wing corrugation and bee body in flapping flight aerodynamics to unravel the true load-lifting capacity of bumblebees.