With a corkscrew movement, worms wriggle themselves out of the knot at lightning speed

To get through dry periods, groups of brittle silt worms roll up into messy balls. But as soon as they spot danger, they manage to wriggle free thanks to a special spiral twisting movement.

Worms that form intricate, entangled tangles with their bodies manage to free themselves in milliseconds when they feel threatened. That fast denouement is due to special, spiral movements that each worm makes, according to research.

Brittle sludge worms (Lumbriculus variegatus) live mainly in shallow places in the ponds and lakes of North America. During dry spells, they entwine their bodies in reticulated “worm blobs” to keep moist. In the wild, such a ball can contain up to 50,000 worms. It takes a few minutes for the animals to knot themselves into such a blob. But then bioengineer Harry Tuzon of the Georgia Institute of Technology shined ultraviolet (UV) light on one of these worm balls, he was amazed to see the critters wriggle free in a matter of tenths of a millisecond.

Worms in the gelatin

Tuazon and his colleagues wanted to understand how the worms were able to detach from each other so quickly: more than a hundred times faster than it took to form a blob. Using ultrasound, they were able to ‘see’ into blobs of about 20 worms in size. For example, they could see how many times each worm was wrapped around another worm.

To study the worms properly, they encapsulated a worm ball in gelatin so that the worms would wriggle less. They then placed the gelatin worm blob in a shallow container of water and startled the animals with electric shocks or UV light. They filmed the lightning-fast worm denouement, and manually tracked each worm’s path.

Mathematicians help unravel the knot

The bioengineers also enlisted the help of mathematicians who specialize in knot theory. These mathematicians used the observational data to build a mathematical model and run computer simulations. They revealed the big difference between the slow knot and the fast denouement: the direction in which each animal made a kind of spiral wobbling movement.

A repetitive corkscrew movement in one direction, and then an abrupt switch to another, causes the animals to become entangled. But a quick alternating movement between left and right ‘corkscrews’ causes the blob to unbutton efficiently, says bioengineer Vishal Patil from Stanford University in California.

‘I had thought that untangling could not really be solved mathematically, because it is so complex. But then Harry and his colleagues showed us these videos and we thought, if worms can solve this problem, so can we,” he says.

Smart materials can learn from squirming worms

Understanding how sludge worms roll up into a firm blob and then unravel could help researchers with “the dream of creating a material that can do things on its own,” says physicist Antoine Deblais from the University of Amsterdam. In the future, materials made from entangled soft filaments could become looser and more pliable, or harder and more compact if those filaments could wiggle like worms, he says.