I've occasionally seen this critter in North Carolina greenhouses. My
invertebrate sources do list _Turbellaria_ as carnivorous, but only preying
upon small invertebrates. I think the size of most earthworms would
prevent attack. For folks who haven't seen these things, they are large
planaria-like flatworms (about 20 cm when I've seen them). Neat gliding
locomotion. You might try using lime on the areas they infest. Some
inverts can't take the alkaline pH. Alternatively the diatomaceous
earth may make life equally difficult for the critters. Just don't cut
the into pieces, since some of these things regenerate from body
fragments. Good Luck.
Jeff in NC