The honey bee stinger: An unusual pump with collapsible double pistons

Most stinging animals deliver venom by contracting muscles around a venom reservoir, but honey bees employ a fundamentally different strategy. The stingers of worker bees have the unique ability to autotomize, separating from the body, to continue to sting independently. Despite more than a century of anatomical descriptions, the mechanics of venom pumping have remained unresolved due to the challenges of observing them in action. We recorded high-speed videos of active, autotomized stingers, combined with micro computed tomography-based three-dimensional reconstruction to characterize the biomechanics of stinging in the honey bee Apis mellifera. We reveal that the stinger functions as a unique double-piston micro-pump. Two lancets, each possessing a deformable valve, slide in antiphase within a bulb chamber. These valves dynamically deform to alternately form a seal during the downstroke and collapse during the upstroke, enabling pressure generation for pumping while potentially minimizing backflow during refilling. The inverted tear-drop shape of the bulb facilitates refill even while pumping proceeds. We explored valve deformations and flow behavior by constructing a dynamically scaled physical model of the bulb chamber confirming key features of the pumping cycle and propose mechanisms for valve deformations. The double piston design adds significant design complexity but enables continuous venom delivery in a compact, autonomous unit. These findings provide deeper understanding of venom pumping in honey bees and other Hymenoptera. This study also provides evidence of an axial piston pump within a biological system and offers inspiration for the design of microfluidic pumping devices.