Abstract – Landing on a moving target is challenging for flying animals, particularly under dynamic outdoor conditions. For pollinators such as bumblebees, wind-induced flower motion adds substantial complexity to landing manoeuvres. Here, we investigate how bumblebees (Bombus terrestris) land on laterally oscillating flowers. Using high-speed stereoscopic videography, we quantified three-dimensional flight kinematics of 48 bumblebees approaching a sinusoidally moving flower-mimic and analysed their control strategies using system-identification and control-theoretic modelling. Landing dynamics were consistent with combined visual (optic-flow) and angular yaw-rate feedback, enabling precise sideways tracking and gaze stabilization. Sideways motion was captured by a proportional controller, whereas gaze control required a proportional–derivative structure. Both controllers yielded similar case-specific effective delays (approximately 54 and 52 ms). Surprisingly, optic-target-angle contributed negligibly to gaze control, indicating reliance on velocity-based rather than position-based cues. Lateral acceleration correlated strongly with body roll, consistent with the helicopter model of force redirection. These results reveal a modular visual–inertial control strategy enabling robust landings on moving targets and suggest principles for agile bio-inspired flight.

To generate aerodynamic forces required for flight, two-winged insects (Diptera) move their wings back and forth at high wing-beat frequencies. This results in exceptionally high wing-stroke accelerations, and consequently relatively high acceleration-dependent fluid forces. Quasi-steady fluid force models have reasonable success in relating the generated aerodynamic forces to the instantaneous wing motion kinematics. However, existing approaches model the stroke-rate and stroke-acceleration effects independently from each other, which might be too simplified for capturing the complex unsteady aerodynamics of accelerating wings. Here, we use computational-fluid-dynamics simulations to systematically explore how aerodynamic forces and flow dynamics depend on wing-stroke rate, wing-stroke acceleration and wing-planform geometry. Based on this, we developed and calibrated a novel unsteady aerodynamic force model for insect wings with stroke accelerations. This includes improved versions of the translational-force model and the added-mass force model, and we identify a third novel component generated by the interaction of the two. This term reflects the delay in bound-circulation build-up as the wing accelerates. The physical interpretation of this effect is analogous to the Wagner effect experienced by a wing starting from rest. Here, we show that this effect can be modelled in the context of flapping wings as a stroke-acceleration-dependent correction on the translational-force model. Our revised added-mass model includes a viscous force component, which is relatively small but not negligible. We subsequently applied our new model to realistic wing-beat kinematics of hovering Dipteran insects, in a quasi-steady approach. This revealed that stroke-acceleration-related aerodynamic forces contribute substantially to lift and drag production, particularly for high-frequency flapping mosquito wings.

When approaching a landing surface, many flying animals use visual feedback to control their landing. Here, we studied how foraging bumblebees (Bombus terrestris) use radial optic expansion cues to control in-flight decelerations during landing. By analyzing the flight dynamics of 4,672 landing maneuvers, we showed that landing bumblebees exhibit a series of deceleration bouts, unlike landing honeybees that continuously decelerate. During each bout, the bumblebee keeps its relative rate of optical expansion constant, and from one bout to the next, the bumblebee tends to shift to a higher, constant relative rate of expansion. This modular landing strategy is relatively fast compared to the strategy described for honeybees and results in approach dynamics that is strikingly similar to that of pigeons and hummingbirds. The here discovered modular landing strategy of bumblebees helps explaining why these important pollinators in nature and horticulture can forage effectively in challenging conditions; moreover, it has potential for bio-inspired landing strategies in flying robots.

Insects are among the most agile natural flyers.Hypotheses on their flight control cannot always be validated by experiments with animals or tethered robots.To this end, we developed a programmable and agile autonomous free-flying robot controlled through bio-inspired motion changes of its flapping wings.Despite being 55 times the size of a fruit fly,the robot can accurately mimic the rapid escape maneuvers of flies,including a correcting yaw rotation toward the escape heading.Because the robot's yaw control was turned off,we showed that these yaw rotations result from passive,translation-induced aerodynamic coupling between the yaw torque and the roll and pitch torques produced throughout the maneuver.The robot enables new methods for studying animal flight,and its flight characteristics allow for real-world flight missions.2017