What species is this worm?

I was at the park lying on the grass and its the third time I have seen them, I used to think they were parasites when I was like 7. It is the very small brown worm on the green leaf. It moves by squiggling. It comes in different colors but same size.

http://postimg.org/image/ea3x2nw95/ http://postimg.org/image/zfawh9pr1/

Answer

For me it looks like an inchworms which are the larvae of geometer moth or Geometridae.

By your picture it is almost impossible to see of which type it is.

I took picture of one in Switzerland (but likely not the same as yours).

Full resolution here: https://flic.kr/p/utFsiU