Fairies at dusk

Whilst in the garden this evening we were intrigued by seeing many brightly glowing dots of light dancing above the roofs of nearby houses, wondering what they were.  First theory was that one of the neighbours' children was blowing soap bubbles and these were catching the light of the low sun and shining against the grey clouds.  A look through binoculars showed that the movement was not random and the shining dots were insects.  My best guess was it was a synchronised emergence of mayflies.  The swifts and martins seemed to be enjoying it anyway.