The Green Shield Bug (Palomena prasina) is a shield bug within the Pentatomidae family.
Shield bugs undergo a simple metamorphosis, where the newly hatched juveniles, or nymphs, resemble the adult insects in their shape and vary mainly in size.
As the nymphs grow from late May to August, they change color to include spots or markings, depending on the species of shield bug.
While in the nymph stage, shield bugs are flightless and spend most of their time feeding on vegetables and fruits.

1st & 2nd photo: 's Graveland, The Netherlands, 31 August 2011
3rd photo: 's Graveland, The Netherlands, 13 June 2011
4th photo: A nymph. In my yard, Hilversum, The Netherlands, 5 September 2015
5th photo: A nymph. Oostvaardersplassen, The Netherlands, 25 September 2011