I purchased several Japanese Painted Ferns at an end of year clearance from a big box store (I couldn't pass up the price of 50 cents per quart on these guys). Though after I had them home prior to planting I noticed on at least half of them were these worm/centipede type things in the centers. They're opaque, have antenna a whole lot of hair like legs, very thin, about a quarter to half inch long and have a 'crunchy' exterior (they crunched when I squished one). They curl up in a ball and are not very fast when moving around. I'm trying to figure out what they are so I can get rid of them before transplanting to my garden.
