Tiny caterpillars descending on silk

[lobnett]

Hello, I'm new to this. I haven't got a picture but we were invaded by some tiny caterpillars at school. The caterpillars came down from the ceiling tiles on a silk thread. They were approx 1mm long and very thin. I whacked one under a microscope and it was brownish coloured, bristled and had 6 little legs at the head end. The head end was black. It possibly had 2 feet/clasper-type things at the tail end.
If anyone has any ideas based on this rather crude description, I would be very grateful!