We found this large yellow underwing moth Noctua pronuba crawling across a pavement just after it had hatched from its pupal case. At that point the wings were very small - about one third of the length of the body - but by the time I'd carried it home, after half an hour later, they had almost fully expanded.
It sat on a leaf holding its wings vertical above its back for the final stages in their development, revealing the bright yellow underwings and also ....
... this small bristle on the underwide of the lower wing, which seems to lock into a slot on the underside of the upper wing - presumably a mechanism for holding them together in flight to produce a larger, more rigid wing surface.
Here the wings are about 90% expanded and you can see the yellow 'flash coloration' that is thought to alarm and deter predators when they disturb the moth.
While it was extending its wings the moth also had a practice uncoiling of its proboscis.
Finally, here it is, fully winged and ready for flight. A dull-looking moth until you disturb it and it exposes those colourful underwings.
These moths are very vulnerable in the hours between their emergence and the final development of their wings - click here for images of one that was not so lucky....