While mandibles are primitive and chewing, insects may have highly modified mouthparts, e.g., sponge-like mouth of housefly. As with other arthropods, these limbs may become highly modified by evolutionary selective pressure, e.g., the gripping forelimbs of a praying mantis vs. the jumping hind limbs of a grasshopper. Wings are modified cuticle, so are analogous to bird wings, but not homologous . Veins in the wings represent where blood supply, etc., once existed. Internally, an insect will have many general similarities to other arthropods.
Flight offers major benefits to insects.
Indirect flight muscles contracting on the exoskeleton account for the upstroke. In either case, the wing angle keeps changing to account for change in directions. These stages live in different areas and eat different foods. The front pair of the beetles' two sets of wings are thickened into hard covers. These fold back into an effective shield, protecting the soft body underneath, hence the order name.