For humans, traversing an open field is typically faster than navigating a cramped underground tunnel. However, the opposite holds true for microscopic worms. According to research published on July 28 in Physical Review Letters, these tiny organisms actually accelerate when squeezed into tight spaces, moving significantly faster through confined channels than across wide, open areas. This counterintuitive discovery could inspire the development of advanced, soft robotic systems capable of navigating earthquake rubble or traveling through the human body for targeted drug delivery.
In their experiments, scientists utilized California blackworms (Lumbriculus variegatus), which are slender, highly flexible aquatic creatures measuring roughly 0.05 centimeters in width and 2.5 to 5 centimeters in length. The researchers guided the worms through water-filled glass channels open at both ends. When the channel width was constrained to roughly twice the worm’s body diameter, the creatures propelled themselves rapidly, crossing the channel in about a minute. In contrast, navigating wider channels took the worms up to five times longer.
To understand this phenomenon, the research team developed computer simulations modeling the worms as active “beads-on-a-string.” These virtual models replicated the physical behavior of the real organisms under confinement. “It was much faster in the smallest confinement,” noted physicist K.R. Prathyusha at the University of Colorado Boulder.
The team’s mathematical framework revealed that a worm’s speed is a function of its flexibility and the space available to it. In wider channels, worms tend to flail and reorient themselves, wasting energy in unproductive movements. Conversely, tight confines restrict lateral movement, forcing the worms to utilize the channel walls for physical support and push forward in a streamlined, efficient manner.
Saad Bhamla, a biomolecular engineer at the University of Colorado Boulder, highlighted the potential applications of this unique locomotion. He explained that understanding how worms move through tight, narrow passages could inform the design of autonomous soft robots meant for industrial pipe inspections or medical procedures, such as delivering therapeutics inside the human body.
Computer simulations of worms moving through channels helped researchers learn or understand how fast the worms move based on their stiffness and the width of the channel. K. R. Prathyusha
To distill the physics behind this behavior, the researchers analyzed the ratio of the squared channel width to the worm’s stiffness. When this ratio is low—indicating a stiff worm in a tight space—the organism moves almost linearly, like a bullet. However, a high ratio results in constant, inefficient wriggling that drastically slows transit times.
David Hu, a bioengineer and roboticist at Georgia Tech who was not involved in the study, remarked on the rarity of this biological phenomenon. “That is very rare in nature, that if you have less navigation room, things get faster,” Hu observed, pointing out that snakes, by contrast, slow down in narrow spaces. Raghunath Chelakkot, a physicist at the Indian Institute of Technology Bombay, also commented on the study, noting that while biological systems are inherently messy and complex, the researchers’ simple model successfully captured the essential physics of worm translocation.
