These bugs are commonplace in British gardens, often basking on leaves in the sun. Being true bugs (see this post for further explanation here) they bite into the stalks of plants to drink the sap. However, they do not cause any significant damage. Their American cousins are known as stink bugs. The UK bug has a distinctive dark patch on the bottoms of the wings, unlike the recent invader from Europe, the Southern Green Shield Bug.
They hibernate through the winter as adults, then after mating, lay eggs underneath leaves. After hatching they go through a wingless nymph stage, before developing into the adult form. I found one nymph lurking in amongst my St John’s Wort.
It seems that these bugs are spreading north into Scotland due to the warming climate, this website here is tracking their movements, so if you see one you can submit your sighting to them.
They are not to be confused with Green Shield Stamps, an early shopping loyalty scheme which saw elderly ladies in the UK obsessively collecting stamps to fill their books in the 1970s, so that they could buy treats for their young charges in the Co-op. Jethro Tull allude to these stamps in their song, “Broadford Bazaar”. For those of you who are unfamiliar with their music you can have a listen here. Enjoy the song and remember there is no need to spray pesticide on your Green Shield Bugs.