I live close to the sea. A half mile up the beach there is a small stream that eternally fights with the incoming waves. Some time ago, down on my knees looking carefully into this stream I saw my first hairworm. Within ten minutes I had a dozen of these worms in a large glass jar. I brought them home with the intention of putting them into a tank. The evening was late so I thought to leave the worms in the glass jar until morning before transferring them to the more spacious tank.

Hairworms, of which there are many species around the world are, as their name implies, no thicker than a hair. Some are short, no longer than a few centimetres in length. Others can grow up to a meter long. (My hairworms were about 15 centimetres in length.) Prodigious numbers of eggs are laid in strings in water. When the larva hatch out they are so small that they commonly get ingested by insects. They develop inside the host and break out through the body wall when adults and enter water once more to mate and produce more of their kind. All of this is straight forward enough and well known but what I do not understand is what I observed in the glass jar the following morning.

All of the worms were hanging vertically and close together like a loosely braided rope. Not only that but they were spinning extremely fast. I know that hairworms when mating do so in a very tight ball. But this was no ball. I wondered was this spinning an attempt to increase the oxygen level in the water? I left them in the glass jar for 12 hours to see if anything further would happen. For that full 12 hours these worms continued to spin at the same furious rate – never once slowing down. How they could sustain that energy output is a mystery to me. And of greater importance – what was the reason for this behaviour?

Can anyone offer me clarification on what these worms were doing please?