Thousands of flies landed on an oil rig in the North Sea. Scientists finally think they know why

An oil rig in The North SEa - (Getty/iStock)

On a North Sea oil rig several years ago, an engineer noticed a strange phenomenon. A cloud of insects would descend from the sky and land on the upper reaches of the platform.

There were thousands of them, carpeting the superstructure and barely moving. They would sit there for a few hours, then suddenly they would all rise up into the sky and fly off again.