If you don't get an answer here, you could try the "Insects" and "Name This Animal" forums on Nature.Net (maybe both, since neither one seems very busy).

At the top of this page, mouse over the heading "Forums" and select "Nature Forums."

Was the critter segmented like a worm? You said "as thin as a root" -- one millimeter? two?

Possibly a 'horse hair worm." They are parasitic to many bugs and beetles.

Sounds like a Horsehair worm to me too:

http://entoplp.okstate.edu/ddd/insects/horsehairworms.htm

http://www.ag.ndsu.nodak.edu/aginfo/entomology/entupdates/Indoor_pest/horsehair_worm.htm

Look and see if it is the cut worm that is posted on my photo bucket below is your worm. I look in the morning and night for these nasty worms.

Here is a link that might be useful: my pool container garden

You guys rock! Thats it: a horsehair worm. What a strange looking little worm.