This Green Shieldbug, Palomena prasina, got into our conservatory a few days ago. There are two common green shieldbug species. This one is easy to identify as its wing membranes are dark. The other one, Nezara viridula, a recent invader of the U.K., has transparent wing membranes. The Green Shieldbug is a large species, bright green, with yellowish-red legs and antennae. It flies readily and this specimen flew away from the breakfast bowl after I took its photo. Shield bugs develop from nymphs in several stages that lack wings and might resemble little to the adult. The Green Shield bug has five such instars. The adult overwinters, and before doing so, it acquires a darker, purplish colour. After overwintering, they turn bright green again. Egg laying proceeds at around June and the successive instars develop during the summer, before the new generation of adults emerges in September.
An early instar of Green Shieldbug (30 July 2010)
A fifth instar (4 Oct 2010) Wing buds are visible.
For a great website to identify British bugs, including instars, see British Bugs.