From back in early June: a final instar nymph of the forest bug, Pentatoma rufipes (Hemiptera: Pentatomidae). The developing wings can be seen as the dark stubs on each side of the back (behind the blue 'shoulders').
This is a slightly earlier instar nymph of the same species from back in May. The wing stubs have not yet started growing.
Photos taken Whiteknights Park, Reading University grounds, Reading, UK, on 2011-06-01 and 2011-05-13, respectively.