This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Australian scientists have used high-speed video to uncover the unique mechanism that allows a honey bee's stinger to continue to pump venom into its target even after it has separated from the bee's body. A new study, published in the journal PNAS, reveals for the first time that the tiny 2-millimeter (0.08-inch) stinger of the honey bee (Apis mellifera) works as a sophisticated double-piston micropump.
"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," said Ramirez-Esquivel.
After a worker bee lands and thrusts its stinger into the target, it flies away, leaving the stinger behind in a process called "autotomy." The stinger then continues to penetrate the target tissue and inject venom under its own power. By having bees sting a clear gel that mimics human skin, researchers from Macquarie and the University of New South Wales were able to record video of the autonomous action of the stinger pumping venom for the first time. The stinger contains several different components, including a venom sac and pumping chamber, muscles and nerves.
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 these 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 showed that the valves inflate like a parachute on the downstroke, functioning as pistons to apply downward pumping pressure on the venom in the chamber, then deflate on the upstroke. "Finally, and perhaps most dramatically, as the valves meet in the middle of the stroke, they change shape again to push past each other," said Ramirez-Esquivel. "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 further explored the mechanics and flow of the stinger by using microCT scans to 3D-print a scaled-up working model, or small robot, of the bulb chamber and lancets, which confirmed key features of the pumping cycle. "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," said Ramirez-Esquivel. The study authors conclude that the design principles they have uncovered in the honey bee stinger could provide inspiration for engineered micropumps with potential applications in minimally invasive medical and microfluidic technologies.
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