Sperm cells have fooled scientists for centuries: They don't 'swim', they move as their tails 'spin'

Sperm ‘drills’ into the fluid like a spinning top by rotating around itself whilst its tilted axis rotates around the centre. When Leeuwenhoek first discovered sperm, he described it as a “ living animalcule ” with a “tail, which, when swimming, lashes with a snakelike movement, like eels in water”. We needed a super-fast camera capable of recording over 55,000 pictures in one second mounted in a fast oscillating stage to move the sample up and down at an incredibly high rate – effectively scanning the sperm tail while swimming freely in 3D. The sperm’s rapid and highly synchronised spinning causes an illusion when seen from above with 2D microscopes – the tail appears to have a side-to-side movement.