Mood indigo

Pottering around the garden this afternoon, I came across a group of at least eight Green Shieldbugs resting on adjacent leaves in one of the Norway maples. This was interesting in itself because I'd never seen this behaviour before, but even better, this one was repeatedly opening and closing its wings - revealing the upper surface of the abdomen, which is concealed and protected by the wings when they're folded, to be a glorious iridescent purple colour.

I initially assumed that the shieldbug was preparing to fly away, so I rattled off a quick burst of shots without worrying about the angle, or taking too much notice of my settings, neither of which were ideal for this kind of image. In fact it turned out that the bug was simply unhappy with the way its wings were folded and was trying to rearrange them, and as this performance went on for quite a while before it was finally satisfied, I would have had plenty of time to set the shot up better - but it's easy to be wise about these things with hindsight. 

Apart from that sensational abdomen, I think the best thing about this photo is that it gives a sense of the mechanism involved in the unfurling of a shieldbug's wings. Both the pronotum (the shoulder plate, immediately behind the head) and the triangular scutellum have to move up and forwards to free the forewings, which then pivot forwards, allowing the hind wings to unfold. In flight the fore and hind wings on each side work as single units, because the rear edge of each forewing 'clips' to the front edge of the corresponding hind wing by means of a structure that somewhat resembles the ziplock top of a resealable food bag. When the wings refold, the clavus, which is the slender rear section of the hardened portion of the forewing (the long thin triangle running down the right forewing here) slides into a groove on the outer edge of the scutellum. The scutellum and pronotum then move backwards and downwards, and the shieldbug's armour plating clicks back into place.

R: C5, D21.