Rafts of tiny purple insects

[mixer]

I've just found in my back yard several rafts of tiny purple insects. They were in two small puddles - about twice the size of my palm. Each raft had hundreds of these insects which when I looked more closely were wriggling. Any on drier land where the water had evaporated looked to be struggling as far as i can tell as they were very small - 1-2 mm in length. They seem to have appeared overnight as I didn't notice them yesterday. I live in rural North Yorkshire, Wensleydale at around 190m. The weather has just turned more inclement with temperatures varying widely from 5C to around 14C and wetter.

Any suggestions?

Mixer

[tristanba]

these sound like aquatic Collembola, something like Podura perhaps