They seem to spin some kind of silk everywhere they go. They seem to be no longer than about 4 mm. I noticed them crawling up things and then dropping down on a line of silk. I've started catching them by putting little sticks up in the air attached everywhere that I find them. They tend to gather at the top of the stick for easy rapture by vacuum.
It's a larva of the Laugher moth, they are spinning the silk so they can go from their caterpillar form into their moth form.