Blackworms Move Faster Through Tight Tunnels Than Open Water, Study Finds

For humans, crossing an open field is faster than crawling through a tunnel. For a tiny worm, it's the opposite. In a study published July 28 in the journal Physical Review Letters, researchers found that California blackworms move much faster through a tight, confined channel than through a wide-open one.

The team studied Lumbriculus variegatus, slender aquatic worms about 0.05 centimetres wide and 2.5 to 5 centimetres long, by letting them glide through water-filled glass channels open at both ends. When a channel was only about twice the worm's width, the worm shot across to the other end in about a minute. In wider channels, the same journey took up to five times longer.

To understand why, the researchers built computer simulations that modelled each worm as a string of active beads, then squeezed the virtual worms through channels of different widths. The simulated worms behaved much like the real ones. "It was much faster in the smallest confinement," said physicist K.R. Prathyusha of the University of Colorado Boulder. The team's mathematical model showed that speed depends on how bendy the worm is and how much room it has to move: in a wide channel the worm flails as it tries to reorient itself, but a narrow channel blocks that flailing, so the worm braces against the walls and squeezes straight ahead.

Biomolecular engineer Saad Bhamla, also at CU Boulder, said the finding could guide the design of soft, autonomous robots that crawl through pipes or navigate inside the human body. "It seemed like a very relevant problem, that some physics would help engineers design things," he said. Bioengineer David Hu of Georgia Tech, who was not involved in the study, called the result unusual: his own 2012 study had found that snakes, unlike the worms, slither more slowly through narrow channels. "That is very rare in nature, that if you have less navigation room, things get faster," Hu said.

Physicist Raghunath Chelakkot of the Indian Institute of Technology Bombay, who also was not involved in the research, said the study's value lies in how a simple model captured a real biological behaviour. "Biological systems are messy and complex," he said. "What I find interesting is that with such a simple model, they could capture some essential features of this worm translocation."