unknown larva worm

[D D]

I recently found this insect under some pots in the garden. to me it seemed like a larva or worm.

I can only describe it as truly disgusting! - when still it looked like any other worm but once it was touch (with a stick) it shot out a this thin white filament from one end in lightning speed and wrapped it around the stick! Another time it dragged itself along the ground with it. It happened so fast I couldn't get a decent photo - i did get some footage though.

The Comic book character named 'Venom' springs to mind when looking at it in action - very freaky.

ANyway - has anyone seen this, can they identify it, or if not any advice on a possible website/book to identify it?

D D
PS (I know it may not be a butterfly/moth larva but you guys and gals on this sight are such keen naturalists I thought you might know)