California blackworms move faster in tight spaces, study finds

In a finding that defies intuition, California blackworms move faster when given less space, researchers report.

For humans, running across an open field is faster than crawling through a narrow tunnel. But for the slender aquatic worm Lumbriculus variegatus, the opposite is true.

The study, published July 28 in Physical Review Letters, found that the worms squeeze through confined spaces much faster than they wriggle across wide ones.

In experiments, researchers used blackworms that are about 0.05 cm wide and 2.5 to 5 cm long. They let the worms glide through water-filled glass channels open at both ends. When the channel width was about twice the width of the worm, the creatures shot forward and reached the other end in about a minute. In wider channels, up to 8 mm wide, they took up to five times longer.

The team also created computer simulations modeling the worms as active beads-on-a-string. The virtual worms behaved similarly.”It was much faster in the smallest confinement,” said physicist K.R. Prathyusha, who led the work at the University of Colorado Boulder and Georgia Institute of Technology.

According to the mathematical model, speed comes down to how bendy the worm is and how much wiggle room it has. In wider channels, worms flail about as they reorient. A confined space restricts reorienting, so with nowhere else to go, they use the walls for support and squeeze forward.

The findings could help engineers design better worm-like soft robots that could crawl through rubble after an earthquake or move through tubes inside the human body.