Scientists find California blackworms have an unexpected advantage in tight spaces: The worms escape narrow channels faster than wider ones, a finding that could influence the design of soft robots

A narrow passage would seem like the last place an animal should move quickly. With less room to turn, bend or change direction, it should be harder to get through. But California blackworms appear to have a different strategy.

New research has found that these flexible, self-propelled worms can move faster through narrow channels than wider ones. The reason is surprisingly simple: when space becomes tight, the walls help keep the worms pointed in the direction they need to go.

The July 2026 study, published in Physical Review Letters, combined experiments on California blackworms (Lumbriculus variegatus) with computer simulations of self-propelled flexible filaments. Researchers led by K. R. Prathyusha and colleagues at the Georgia Institute of Technology found that stronger confinement suppressed the worms' tendency to turn and explore, effectively making the walls of a narrow passage a guide.


The finding could also help engineers design soft, worm-like robots capable of navigating pipes, tunnels and other confined environments.

More space made the worms slower

The researchers tested blackworms roughly 0.5 millimetres in diameter and 50 millimetres long in channels of different widths. These worms typically live in shallow-water marshes, ponds and swamps, where they feed on microorganisms and organic material. In the narrowest channels, they tended to align their bodies with the channel and move directly toward the exit.

However, when the researchers increased the available space, the worms became less efficient. They bent, changed direction, explored sideways and frequently paused before continuing forward.

The difference was substantial. In channels with a scaled width of about 2 times the worm's diameter or less, the worms escaped in an average of 56 seconds. In wider channels, their average escape time rose to roughly 299 seconds, more than five times longer. The computer simulations showed the same broad pattern.

Why does a narrow passage help?

The researchers say the key is reorientation. A worm does not simply propel itself in one perfectly straight direction. Its flexible body bends and changes shape as it moves. When there is plenty of room around it, those movements can send the worm in different directions.

That extra freedom turns out to have a cost. In wider channels, the worms frequently stopped, bent their bodies, and reoriented themselves before moving forward again. The researchers observed what they describe as “stop-go” motion, where periods of forward movement were interrupted by pauses during which the worm's head explored its surroundings.

A narrow channel takes away much of that freedom. The walls restrict sideways movement and encourage the worm to align its body with the channel. Once aligned, its self-propulsion is directed mainly toward the exit.

In effect, the narrower passage acts like a physical guide rail. The researchers found that this effect was strongest when the channel was close to the worm's own diameter. As the channel widened, the opportunity for sideways exploration and reorientation increased, slowing the overall journey.

The result goes against what happens with DNA

The finding is particularly interesting because confinement usually makes the movement of passive polymers more difficult.

DNA, for example, is a long, flexible molecule that can move through tiny biological pores. When such passive polymers are squeezed into narrow spaces, confinement can create an entropic barrier that makes translocation harder.

“California blackworms, however, are very different from DNA,” Prathyusha explains in a column in The Conversation.

The blackworms are different because they follow a system called ‘active matter’. Unlike DNA, they continuously generate their own movement. Their muscles and flexible bodies allow them to propel themselves forward, meaning the walls of a channel can actually help organize that movement rather than simply obstruct it.

The researchers also created a simplified computer model to understand whether the effect depended on the complex biology of a real worm.

The simulated filament had no muscles or nervous system. Instead, it consisted of a flexible chain of tiny connected units that continuously propelled themselves forward.

Yet the model reproduced the central result: stronger confinement encouraged alignment and faster escape, while wider channels allowed more reorientation and slowed the filament down.

Flexibility matters too

The study found that the outcome also depends on how flexible the filament is. Stiffer filaments tend to remain aligned with the channel, allowing them to move more directly. More flexible filaments can bend and form irregular shapes, making them more likely to reorient when given additional space.

This affected the likelihood of successfully navigating the channel. Under strong confinement, the success rate was close to 100% regardless of filament stiffness. In wider channels, however, flexible filaments were more likely to become caught in repeated changes of direction, back-and-forth movement or other behaviors that prevented them from reaching the exit within the observation period.

The researchers developed a single dimensionless measure that combined channel width and filament stiffness and captured the transition between these two movement regimes.

Could worms teach robots how to move?

The researchers say the finding could have implications beyond understanding worms. Soft robots are being designed to bend, squeeze and move through environments that conventional machines struggle to navigate. Such machines could eventually be used for applications including pipe inspection, medical procedures, drug delivery and exploration of difficult-to-reach environments.

The usual engineering instinct might be to give a robot as much space as possible. The blackworms suggest that this may not always be the best strategy.

The author concluded that their discovery might help in science’s quest to build soft robots. ‘Our results suggest an unexpected perspective: Confinement does not always hinder movement. For soft robots, narrower paths could sometimes be an advantage, helping future robots navigate tight spaces, whether delivering drugs or performing minimally invasive procedures inside the human body, or inspecting hard-to-reach sections of industrial pipelines.’