Folding valves keep a detached bee stinger pumping venom

The valves have a third trick, and it is the one that makes continuous flow possible. Midway through the stroke the two valves change shape again and slide past each other. "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 Fiorella Ramirez-Esquivel, a study co-author and entomologist at Macquarie University ^[7][11]. Because the valves pump in opposite directions, she said, they can deliver a continuous flow of venom ^[1].

Ramirez-Esquivel also described the cost of that design. "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," she said ^[8]. The same design accounts for the detached stinger: the whole pump, sac to valves, travels with the barb.

The question is old. "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," Ramirez-Esquivel said in a statement ^[10]. The team's first tool was a clear gel that mimics human skin, which bees stung while a high-speed camera recorded the stinger ^[3]. The gel tests don't show how a detached stinger behaves in living tissue. The gel is a stand-in for skin, so the footage shows how the parts move, and says little about how flesh pushes back.

The second check is the stronger one. The team made microCT scans of the stinger, used them to 3D print a model of the bulb chamber and lancets, and reported that the model confirmed the key features of the pumping cycle ^[9]. A printed copy that reproduces the cycle shows the geometry is sufficient to pump; whether anything else in the living stinger contributes is still open.