About 3" long when fully extended, I think. The thickness of sewing thread and a white/off-white colour. It was clinging to the edge of a pot with what appear to be "feet". It frequently raised its head and front end and moved around as though it was looking for something. I saw it back in May and have been trying to identify it since then.
It will be one of the nematomorph worms, AKA Horsehair worms, Thunder worms, Gordian worms. They are parasites of invertebrates and are often seen in wet humid weather.
See wiki here: http://en.m.wikipedia.org/wiki/Nematomorpha
I don't know if I'm splitting hairs here but isn't it more likely to be Mermis (which is a true nematode but does the same thing)? -
Thanks, all. Definitely NOT an elastic band. Whether Nematomorpha or Mermis, I couldn't tell from the relevant websites. They both look equally uninviting, but it's good to know what it was.