Scientists rarely get straight to the point. An ode to unexpected discoveries. Today: How chemists Sander Waterson and colleagues discovered that worms move differently than standard physics predicts.
What happens if you use live worms to study polymer molecules?
It was a Friday afternoon and I was cycling the Javastraat in Amsterdam. I had two small bags of worms in my basket. It was very sunny and the stands were full, but I was on my way to the lab.
My colleagues Daniel Bonne and Antoine Deblis and I have been talking about this experience for some time. They’re physicists, I’m a chemist and we wanted to look together at polymer molecules, the important building blocks of DNA and plastics, among other things. They are chain-shaped and their shape shows many similarities to those of worms, which is why we wanted to check them out.
My research was not expensive. As a teenager, I actually bought Tubefix worms as food for my aquarium. You can get a lot for very little money. On Friday afternoon, I biked to the pet store to buy some bags.
We wanted to look at the worms, because they may resemble polymer particles in shape, but they move in a completely different way. Worms are an example of “active matter,” a substance made up of particles that can generate kinetic energy on their own. Ordinary polymers can’t do that, their movements are random. Worms can “steer” more which is why we found it interesting.
Daniel had a machine that measured the viscosity of a substance. When looking for polymer molecules, this is one of the first things you measure. You can then find out the size and entanglement of the particles. After we put the worms into the machine, a control measurement followed. After all, it was clear that the worms behaved differently than “normal” polymers, but we had to prove that this was because the worms were actively moving around.
“It’s up to us to make the worms inactive. I couldn’t bring myself to kill them. Sure, I fed them my fish as a teenager, but I still felt sad.”
I came across a german study on the internet about amazing snails. The scientists had put the snails in a mixture of water and 5% alcohol, which rendered them ineffective. They even tried different types of beer.
We made sure that the worms were so drunk that they were no longer moving and then were able to perform a control measurement. After this measurement, they quickly got up again, which only took half an hour.
After we measured the worms’ viscosity, something strange happened. We had put the worms in a bowl of water, because they live in water. Then we suddenly saw that they slowly formed a ball full of swarming worms. This in itself is not strange, the polymer molecules do too. What surprised us was the way the ball grew.
Normally, the polymer molecules jump a little and accidentally reach the largest ball. This did not happen in the case of worms. They formed smaller balls that moved as a whole towards the larger ball. This is very different from how droplets usually grow: large droplets grow at the expense of small droplets, because molecules escape from small droplets more easily than from large ones.
It may sound complicated, but this has a fundamental impact on active matter research, for which theory is still incomplete.
What did we do with worms after research? We release them into the trench behind the laboratory.
Sander Wattersen is Professor of Physical Chemistry at the University of Amsterdam.
