A new Australian study has uncovered the incredible power of a bee’s stinger, which continues to pump venom into tissue after the bee has flown away.
The study, published in the journal PNAS, revealed for the first time that the tiny 2mm stinger of the honey bee (Apis mellifera) works as an intricate double-piston micro-pump.
“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,” explained lead author Dr Fiorella Ramirez-Esquivel of Macquarie University.
“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.”
After a bee lands and stings its target, it flies away leaving the stinger behind in a process called ‘autotomy’. The stinger then continues to penetrate into the target tissue and release venom under its own power.
Researchers from Macquarie and the University of New South Wales had bees sting a clear gel that mimics human skin, but it was while filming the sting through high speed video that they were able to witness the autonomous action of the stinger pumping venom for the first time.
The vision showed 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.
Researchers found a bee’s stinger works like a miniature reciprocating saw, with two sharp lancets sliding back and forth to drive it deeper into the skin while delivering venom. The lancets also have specially shaped valves that change shape with each movement, helping pump venom into the sting while preventing it from flowing backwards.
“Finally, and perhaps most dramatically, as the valves meet in the middle of the stroke, they change shape again to push past each other,” Dr Ramirez-Esquivel said. “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.”
Researchers used micro-CT scans to create a 3D-printed working model of the stinger’s pumping chamber and lancets, confirming how the mechanism delivers venom. Dr Ramirez-Esquivel said the double-piston design allowed the stinger to pump venom continuously despite its compact size.
Researchers say the findings could inspire the development of tiny pumps for use in minimally invasive medical procedures and microfluidic technologies, which control the movement of small amounts of fluid.
