Researchers reveal how venomous Glycera dibranchiata bloodworms evert their proboscis in under two seconds by rapidly pumping fluid into a folded tube, inflating it like a balloon to as much as three times its resting length. Ultrasound and pressure measurements showed wrinkled, origami‑like tissues and retractor muscles that enable repeatable extension and retraction (retraction ≈ eight seconds). The team measured a maximum strain of εmax = 2.9, highlighting exceptional elasticity with potential applications for stretchier, more capable soft robots.
Bloodworms Turn Their Mouths Inside Out — Scientists Reveal the Balloon‑Like Trick
Researchers reveal how venomous Glycera dibranchiata bloodworms evert their proboscis in under two seconds by rapidly pumping fluid into a folded tube, inflating it like a balloon to as much as three times its resting length. Ultrasound and pressure measurements showed wrinkled, origami‑like tissues and retractor muscles that enable repeatable extension and retraction (retraction ≈ eight seconds). The team measured a maximum strain of εmax = 2.9, highlighting exceptional elasticity with potential applications for stretchier, more capable soft robots.
08:51 AM, 11/21/2025Science
Researchers have uncovered how ruddy, copper‑toothed bloodworms (Glycera dibranchiata) can rapidly evert — that is, turn inside out — a long, flexible feeding tube called a proboscis. The venomous worms, which can grow to more than a foot in length, deploy the proboscis when threatened or when burrowing, shooting it outward in under two seconds and retracting it in about eight seconds.
The study, reported in a preprint, shows that the proboscis behaves much like an inflatable structure. When fluid is pumped into the folded tube, it expands quickly — stretching to as much as three times its resting length without rupturing. The team measured a maximum strain of εmax = 2.9, comparable to the highly extensible body of the leech Hirudo nipponia (εmax ≈ 3.6) and far exceeding the strain tolerance of human tendons (≈ 0.098).
Key to this performance are the worm’s internal folds and retractor muscles. The mouth tube and intestine are stored in a compact, «buckled» state, while the retractor muscles show pronounced wrinkles and folds that the authors describe as a form of self‑organized origami. Those structures allow rapid, repeatable inversion and retraction without tissue failure.
To investigate the mechanics, researchers filmed the animals in air and in seawater‑infused gelatin that mimics the mudflats where the worms live. They used ultrasound imaging — the same basic technology used in medical settings — to visualize internal movement as the proboscis everted and retracted. The worms were restrained in a 3D‑printed “open‑casket worm coffin” to limit whole‑body wriggling during recordings. The team also measured internal fluid pressure to characterize the physical trigger for eversion.
Results suggest eversion is driven primarily by rapid pressurization: fluid inflates the buckled tube like a balloon in under two seconds, producing an appendage that can extend to three times its length. Retraction is slower but still rapid, typically taking around eight seconds as the fluid is withdrawn and the folded structures collapse back into the body.
“It’s like seeing the behind‑the‑scenes of a magic trick,” said David Hu, a mechanical engineer involved in the work. “We could see the deflated proboscis waiting for action.”
Beyond natural history, the findings have potential engineering implications. The worms’ combination of extreme extensibility, rapid actuation, and structural folding could inspire new designs for soft robots. Many current soft actuators rely on polyurethane films and other materials that do not match the proboscis’s elasticity or repeatable performance.
In short, these bloodworms use a compact, folded architecture plus rapid fluid pressurization to perform a dramatic, repeatable inversion of an organ — a biological solution that may point to better materials and mechanisms for next‑generation soft machines.