Question
Hi, Dr. DeAngelis,

I live in Hawaii and I was lifting my potted plants to check for slugs that may have been hiding during the day, but under some pots, I found what looked to be a few thin white flatworms huddled close to each other.  Both ends of the worms were tipped so the heads weren't distinguishable.  The worms looked like the worm in this photo but were white and had a single black line along the body instead: http://i.dailymail.co.uk/i/pix/2010/04/22/article-1267991-093E327A000005DC-691_4...

Any idea what they could actually be?

Answer
Sean,

This is pretty far outside my area of expertise but I think what you've found is a terrestrial planaria (flatworm, see http://en.wikipedia.org/wiki/Planarian for info). If they were long and thin they might have been a horsehair worm (nematode) instead. Google these terms and see if the images match. Both are harmless to you and your plants.

Jack DeAngelis
http://www.livingwithbugs.com