Still stinging? Bee’s stinger pumps venom after bee long gone

By Stephen Beech

A honeybee’s “remarkable” stinger is a tiny double-piston venom pump, reveals new research.

High-speed video uncovered the “unique” mechanism that allows the 2-millimeter stinger to continue to pump poison into its target — even after it has separated from the bee’s body.

The groundbreaking study, published in the journal Proceedings of the National Academy of Sciences (PNAS), was conducted by scientists in Australia.

Lead author Fiorella Ramirez-Esquivel said: “We’ve known since as early as 1910 that the venom sac of a honeybee stinger empties into a chamber with little pumping elements called valves, but until now we didn’t know exactly how they work.

“If you’ve ever been stung by a bee, you’ll know it’s a very painful process, but now we’ve been able to identify all the working parts packed into the tiny stinger.”

She explained that after a worker bee lands and thrusts its stinger into the target, it flies away leaving the stinger behind in a process known as “autotomy.”

The stinger then continues to penetrate into the target tissue and inject venom under its own power.

By having bees sting a clear gel that mimics human skin, researchers from Macquarie University and the University of New South Wales, both in Sydney, were able to video the autonomous action of the stinger pumping venom for the first time.

Ramirez-Esquivel, of Macquarie University, said: “The stinger contains several different components, including a venom sac and pumping chamber, muscles and nerves.

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Still stinging? Bee’s stinger pumps venom after bee long gone

“It also has two sharp, pointed lancets that slide backward and forward on a system of rails — called the olistheter — in a motion similar to that of a reciprocating saw; the lancets are responsible for working the stinger deeper into the skin and also pumping the venom.

“Each of the long lancets has a valve attached that sits inside the pumping chamber.”

The researchers found the valves dynamically change shape to form a seal during the downstroke and collapse during the upstroke, generating pressure for pumping while minimizing backflow during refilling.

High-speed video revealed that the valves inflate like a parachute on the downstroke, functioning as a piston to apply downward pumping pressure on the venom in the chamber, then deflating on the upstroke.

Ramirez-Esquivel said: “Finally, and perhaps most dramatically, as the valves meet in the middle of the stroke, they change shape again to push past each other.

“This is a remarkable strategy to pump fluid since maintaining a seal is vital to effectively transmit pressure.

“The unique geometry of the valves is the key; they act as collapsible pistons and — by pumping in opposite directions — they’re able to deliver a continuous flow of venom.”

The researchers also explored the mechanics and flow of the stinger by using microCT scans to 3D print an up-scaled working model, or small robot, of the bulb chamber and lancets, which confirmed key features of the pumping cycle.

Ramirez-Esquivel added: “The double-piston design adds complexity, but it’s the key to the stinger being able to deliver venom continuously in a compact, autonomous unit.”

The research team concluded that the design principles uncovered inside the stinger could inspire engineered micropumps with potential applications in minimally invasive medical and microfluidic technologies.