The world’s most renowned TV naturalist, Sir David Attenborough, stands in a tropical forest. It’s dark. Suddenly a pinpoint of green light flashes underneath him, in the grass. Another flash, and another until they become too numerous to count. And then a pattern emerges – instead of random light flashes, which would create a steady background, like individual drops of rain create steady rain noise, the flashing fireflies synchronise. They create a rhythm, not unlike flashing traffic lights – or a lighthouse.
The synchronising of rhythms of individual insects is not limited to the fireflies. Perhaps less surprisingly, bees, the notorious collective, do it. Not the torch-like flashing but they shimmer in response to hornet approach. So do starlings and fish that create mesmerising collective movements.
This type of movement is called metachronal rhythm or metachronal wave. It’s produced by the sequential action (as opposed to synchronized) of structures such as cilia, segments of worms or legs. These movements produce the appearance of a travelling wave.
It’s made by reacting and repeating the movement of your neighbours be it cilia in a single cell organism or a human. West Ham football supporters (and all the rest of them) succumb to a metachronal rhythm during a Mexican wave.
Restless Creatures: The Story of Life in Ten Movements by Matt Wilkinson,
- ASIN: B01B39IRJ2