High-speed video reveals bee’s unique venom pump in action

The tiny torture device that is a honey bee’s barbed sting could be among the most sophisticated of venom-delivery systems in the natural world.

While scorpions and spiders crudely squirt their agony-juice into your flesh, bees use a complex "two-stroke\" pump to delicately inject sweet, sweet pain into their victims long after the bee has flown away to succumb to its self-inflicted trauma.

Despite knowing about this relatively unusual anatomy for more than a century, nobody had ever observed it in action.

“We’ve known since as early as 1910 that the venom sac of a honey bee stinger empties into a chamber with little pumping elements called valves, but until now we didn’t know exactly how they work,” says Fiorella Ramirez-Esquivel, an entomologist at Macquarie University in Australia.

Leading a team of researchers in an investigation of the honey bee’s sting, Ramirez-Esquivel has now captured the process in high-speed video, revealing precisely how two flexible valves work together like a pair of miniature pistons to drive venom deep into target tissue.

The findings not only provide biologists with insight into bee biology but may also help engineers develop new kinds of micropumps for medical devices.

As anybody who has ever incurred a bee’s wrath well knows, their own life comes second to a desire to make you pay. In a process known as autotomy, the assailing bee leaves its stinger operating independently, driven by its own muscles, various glands, neural ganglia, and a venom sac.

The detached apparatus continues to move without the bee’s oversight, burrowing deeper into the tissue while pumping venom through a narrow canal.

To investigate the process in detail, researchers from Macquarie University and UNSW Canberra filmed detached stingers as they penetrated a transparent gel designed to mimic human tissue. They combined the footage with high-resolution micro-computed tomography scans, which allowed them to reconstruct the stinger’s intricate internal structures in three dimensions.

The team confirmed what many had long suspected: the pumping action depends on two long, sharp structures called lancets, which slide back and forth inside a larger stinger component called the stylet. Each lancet carries a flexible valve that moves within an enlarged chamber, or bulb, where venom collects before being expelled.

The valves move in opposite directions, allowing them to alternate between forcing venom out and making room for more to enter. During a downward stroke, a valve expands against the chamber walls, forming a seal and acting like a piston to force venom towards the exit. As it moves upwards, the valve collapses, reducing resistance and allowing the chamber to refill. This change in shape also limits the amount of venom that can be drawn back from the wound.

The two valves must then pass one another midway through their strokes, briefly deforming to squeeze past each other before resuming their pumping roles.

That is an unusual feat for such a small machine. A conventional piston pump typically relies on rigid components and valves to control fluid movement. Here, the honey bee achieves the same objective with flexible structures that continually twist and change shape.

The researchers used their observations to design a 3D model of the pumping chamber. Made using flexible materials, the model reproduced important features of the natural stinger’s pumping cycle, helping confirm how the valves deform and squeeze past each other.

Exactly how the actual valves change shape as they cross remains uncertain. The researchers identified two possible mechanisms, though more work is needed to determine which best describes the process.

The arrangement appears to solve a difficult engineering problem: how to maintain a continuous flow of fluid through such a tiny chamber while simultaneously refilling it.

The system is compact, self-contained, and capable of operating without the bee’s body – something engineers could learn a thing or two from. Devices that move tiny quantities of fluid have potential applications in microfluidics and minimally invasive medical technologies, where controlling flow through narrow channels can be challenging.

The researchers suggest that deformable pistons could be particularly useful in tailor-designed pumps that need to operate within irregularly shaped chambers.

Just one more reason to give the clever little honey bee its due respect.

This research was published in PNAS.

Source: Macquarie University via EurekAlert