Blackworms move faster in a millimetre-wide channel than in open water
The effect turned up first in a bead-chain simulation with no muscles and no nervous system, which suggests the speed-up is physics rather than something the animal decides, and it points robot designers at body stiffness.
The Scientist · Science desk
What happened
- Blackworms crossed a water-filled glass channel about twice their own body width in roughly a minute, and took up to five times longer to get through wider channels.
- The results were reported July 28 in Physical Review Letters, using an aquatic animal about 0.05 centimetres wide and 2.5 to 5 centimetres long.
- The effect appeared first in simulation, where a self-propelled bead chain with no muscles or nervous system kept moving faster through the narrower of two equal-length channels.
Why it matters
- What's now possible capability Bhamla points the result at soft robots inspecting pipes or delivering drugs inside the body, where a machine could be built to press against walls rather than seek clearance, making the tightest stretch of the route the quickest one.
- Who has to decide decision Body stiffness becomes something you set against the narrowest gap the machine is expected to meet, since the fast regime belongs to the pair of numbers and not to the actuator on its own.
- What doesn't add up contradiction Hu's 2012 snake work found the opposite sign, slower slithering in narrow channels, so a confinement bonus cannot be assumed for any long flexible body and does not transfer across propulsion mechanisms.
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The evidence arrived in a specific order, and that order matters. A computational model with no muscles and no nervous system, keeping only a flexible chain and a small push distributed along its length [7], was sent through two channels of equal length, one about as wide as the worm's diameter and one much wider [13]. It kept crossing the narrow one faster, a finding that caught the researchers by surprise [14]. The live-animal experiments came afterwards, designed by graduate student Paulami Sarkar in Saad Bhamla's lab [17], and the simulated worms and the real ones behaved alike [4]. A model with no sensing and no decision-making produces the same effect, showing that the wall helps the animal whether or not the animal notices the wall.
The mechanism the team reports is loss of the freedom to turn. In wider channels the worms flail about while reorienting; in a tight one they cannot reorient, so they brace against the walls and squeeze forward [6]. That compresses into a single quantity: the square of the channel width divided by the worm's stiffness [9]. Small values describe an effectively stiff body travelling almost straight; large values describe a body that wriggles and takes much longer [9]. Because width enters squared, the two terms do not trade evenly, and doubling the gap takes roughly four times the stiffness to hold the same regime [21].
Hold the scale in mind. Twice the width of a body 0.05 centimetres across is a channel about a millimetre wide [20], threaded by an animal 2.5 to 5 centimetres long, which is 50 to 100 times longer than it is wide [19]. About a minute to cross the narrow channel, against up to five times that in wider ones [8][22], puts the penalty at roughly four extra minutes [23].
What was measured is traversal time in a straight, water-filled glass channel open at both ends [3]. Rubble after an earthquake is one of the stated applications [25], and it is a different problem: this experiment used a wall that holds firm when pushed against, while rubble can give way underfoot, and a passage through rubble can simply stop. The reported result also does not speak to energy per unit distance, which is usually the number that binds a soft robot running on a battery.
The physics underneath accounts for the reversal in sign. For a passive polymer such as DNA, tighter pores slow translocation down, since there is less room to bend and change shape [15]. Blackworms drive themselves forward by contracting and bending, which puts them in the class called active matter [16], and self-propulsion appears to flip the sign of the confinement term. Raghunath Chelakkot of IIT Bombay, who was not involved, put the achievement in the right place when he noted that such a simple model captured essential features of the worm's translocation [12]. On the evidence so far I would happily design a pipe-crawler around this and wait for someone to run it in shifting grains before designing a soil machine around it.
What to watch
- Whether the speed-up survives in shifting grains or deformable media, where a wall can give way under the push, rather than in smooth glass.
- Whether a built robot reproduces the width-squared-over-stiffness scaling, and what it costs in energy per unit distance to do so.
- Whether one parameter can be found that covers both the worm result and the slower snakes, or whether the two stay separate cases.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence74
- Adoption
- Not scored
- Hype gap+14
- Incentives55
- Confidence70
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
Researchers report July 28 in Physical Review Letters that California blackworms squeeze through a confined space much faster than they wriggle across a wide open one.
- [2]
California blackworms (Lumbriculus variegatus) are slender, flexible, aquatic animals about 0.05 centimetres wide and about 2.5 to 5 centimetres long.
- [3]
In the experiments the team had the worms glide through water-filled glass channels that were open on both ends.
- [4]
The researchers created computer simulations of the worms as active beads-on-a-string and squeezed them through virtual channels of varying width; the model worms behaved similarly to the real ones.
- [5]
Physicist K.R. Prathyusha of the University of Colorado Boulder said motion was much faster in the smallest confinement.
- [6]
In a wider channel the worms flail about as they reorient themselves; a confined space restricts reorienting, and with nowhere else to go they use the walls for support and squeeze forward.
- [7]
The computational model has no muscles, no nervous system and none of the complexity of a living organism; it retains only a long flexible chain and the ability to propel itself forward, each bead receiving a gentle push along the chain.
- [8]
When the channels' width was about twice the width of the worm, the animals shot themselves forward and reached the other end in about a minute.
- [9]
The team examined the square of the channel width divided by the worm's stiffness; when the ratio is small the worm is less flexible and shoots through almost straight, and when it is large the constantly wriggling worm takes much longer.
- [10]
Bioengineer and roboticist David Hu of Georgia Tech, who was not involved in the work, said it is very rare in nature that things get faster when there is less navigation room.
- [11]
Hu's 2012 paper showed that snakes, by contrast, slither more slowly through narrow channels.
- [12]
Physicist Raghunath Chelakkot of the Indian Institute of Technology Bombay, who was not involved in the work, said he found it interesting that with such a simple model they could capture essential features of the worm translocation.
- [13]
The simulations started with a single worm moving through two channels, each of length twice that of the worm, one about as wide as the worm's diameter and one much wider than its diameter.
- [14]
The simulated worm was consistently moving through the narrower channel faster than the wider one, a result the researcher noticed unexpectedly and found puzzling.
- [15]
Moving through a confined channel or pore is called translocation; because DNA has less room to bend and change shape inside narrow pores, tighter confinement generally slows its motion.
- [16]
California blackworms continuously propel themselves forward by contracting and bending their long flexible bodies, which places them in the class of systems physicists call active matter.
- [17]
The work was done in Saad Bhamla's lab, with experiments on confined worms led by Ph.D. student Paulami Sarkar and computational work joined by undergraduate Justin Xu.
- [18]
In groups, the aquatic worms weave themselves into tangled structures resembling bundles of thread, and the lab had investigated how collections of worms behave under confinement.
- [19]
A blackworm 0.05 cm wide and 2.5 to 5 cm long is 50 to 100 times longer than it is wide.
- [20]
A channel about twice the width of a worm 0.05 cm across is roughly 0.1 cm, or about one millimetre, wide.
- [21]
Because channel width enters the team's control ratio as a square, doubling the channel width requires about four times the stiffness to keep the ratio, and therefore the regime, unchanged.
- [22]
The worms took up to five times longer to get across wider channels.
- [23]
Up to five times an approximately one-minute crossing is about five minutes, a penalty of roughly four extra minutes in the wider channels.
- [24]
Biomolecular engineer Saad Bhamla of CU Boulder was intrigued by how the worms' motion through a narrow channel could apply to autonomous soft robots inspecting pipes or delivering drugs inside the body.
- [25]
The findings could help engineers design wormlike robots that could crawl through rubble after an earthquake or move through tubes inside our bodies.
Sources
2 independent publishers whose own reporting we read for this story.
- sciencenews.orgThese worms move faster when you give them less space
1 article · August 31, 2026
- theconversation.comWorms navigate narrow paths faster than wide ones – these findings could inform robot design
1 article · August 31, 2026
Topics and entities
Topics
- Minimal models of organisms
- Bio-inspired soft robotics
- Confinement and translocation
- Active Matter Physics
Entities
- Physical Review Letters
- Indian Institute of Technology Bombay
- University of Colorado Boulder
- Georgia Institute of Technology
- Raghunath Chelakkot
- California blackworm