When wings are present, the fore-wings are small firm elytra, beneath which the delicate hind-wings are complexly folded.
It has been shown by means of spectroscopic observations that the green colour of the elytra, &c., is due to the presence of chlorophyll; and that the variations of the spectral bands are sufficient, after the lapse of many years, to indicate with some certainty the kind of leaves on which the insects were feeding shortly before they were killed.
The elytra serve as protectors to the wings when the wings are folded upon the back of the insect, and as they are extended on either side of the body more or less horizontally when the insect is flying they contribute to flight indirectly, in virtue of their being carried forward by the body in motion.
1, A), are usually convex above, with straight hind margins (dorsa); when the elytra are closed, the two hind margins come together along the mid-dorsal line of the body, forming a suture.
In many beetles the hindwings are reduced to mere vestiges useless for flight, or are altogether absent, and in such cases the two elytra are often fused together at the suture; thus organs originally intended for flight have been transformed into an armour-like covering for the beetle's hind-body.