The Blue Shieldbug is a smaller species – 5-7mm only compared to around 12mm for the common green one. It has an attractive metallic blue-green with dark wings. It is widespread and favours heath and grasslands, living on low vegetation. It is omnivorous and eats the larvae of leaf beetles, and moth caterpillars, as well as plant matter. The bug overwinters as an adult and lays eggs in the spring. New adults appear from July. There is only one brood per year.
I also spotted an adult Common Green Shieldbug and have added an update photo to that post, as the original was a 4th instar.