The cleanliness and fluoridation of the water supply has dramatically reduced infectious disease and cavities, and has been heralded as one of the 20th century's greatest public health achievements.

They get into the smallest cavities of a house by the time they’re taken hold, it’s gone.

Adding fluoride to community drinking water is credited with reducing the average number of teeth with cavities by 44% in adults and 58% in adolescents since the 1960s, the health service says.

The terrain appears completely untouched by man, but a closer look reveals dozens of cavities pocked across the rolling hills.

By trapping individual bacteria in micro-engineered circular cavities and coupling these cavities through narrow channels, the team observed coordinated bacterial motion.