Who are these Absailing Caterpillars?

For the last few days we've had tiny little green caterpillars (5mm or so in length) descending on wee gossamer style strands from some fir trees in our garden. There can be anything from 4 to 10+ of the little green critters per strand and at any one time there can be up to circa 15 strands blowing around in even the lightest breeze.

Pottering in the garden the last couple of days, I've been coming in from the garden with the little green chums crawling on my clothes and even in my hair!

I had a quick look online, but without a clue, looking up green caterpillars is a non-starter. So I'm asking folks out in the blogosphere if they know what these little green caterpillars on their tiny strands are.