A Meadow plant bug (Leptopterna dolabrata) nymph walks round on a meadow buttercup.
From Wikipedia (http://en.wikipedia.org/wiki/Leptopterna_dolabrata):
Leptopterna dolabrata, commonly known as the meadow plant bug, is an insect in the Miridae family. It is commonly found in grassy areas in North America and Europe. It feeds on developing grass seeds, causing seed heads to shrivel and prematurely whiten. It is regarded as a pest wherever grass is grown for seed.