Induced flow cools hovering bumble bees

Understanding how flying insects manage heat exchange is critical for predicting their survival in dynamic thermal environments. To fly, insects propel air downwards to offset body weight, inducing airflow over their bodies. Remarkably, the potential cooling effect of this self-generated airflow is largely unstudied. We measured induced airflow and wingbeat kinematics for hovering bumble bees (Bombus impatiens) across a range of body sizes and then measured the cooling effect of flows of the same magnitude in a vertical wind tunnel. We combined these data in heat balance models to predict transient and equilibrium body temperatures of hovering bumble bees with and without self-generated wind. Measured self-induced airflow was substantial (up to 1 m s-1), and varied with body size and wingbeat kinematics, contributing significantly to thermal stability. Without this self-induced airflow, bees of all sizes rapidly overheated across a range of environmental conditions, highlighting the importance of this overlooked heat-loss mechanism in the heat budget of flying insects. Our findings suggest that shifts in wingbeat kinematics required for altered force production not only affect energetics and, therefore, heat production but also alter the induced flow and associated convective heat loss.