I was at the park lying on the grass and its the third time ive seen them, I used to think they were parasites when I was like 7. Its the very small worm on the green leaf. It moves by squiggling. It comes in different colors but same size.
Is this what you mean?
It's pretty hard to tell from this photo, and I'm no entemologist, but to me, it looks like it may be a wireworm, a larvae of a click beetle. This is a diverse group, so I think it would be pretty difficult to give a specific identification. (More images)