At each molt they get larger, and genitalia get more complete. Adults are obviously wingless. Newly hatched young are very similar in shape to the adults, but lack genitalia, wings and maybe adult type of cuticle. Most insects gradually acquire adult features. Later instars will have wing pads where the wings are developing.
Genitalia also develop progressively.
This type of development occurs in the Ephemeroptera, Odonata, Plecoptera, and the young of these insects are sometimes called naiads. Each will be discussed in later lectures. The larvae are very different in shape from the adults and a pupal instar is present betwen the last larval and the adult stage to allow for the complete reorganization of the body. In a few holometabolous insects the first instar is also a radically different shape than the older instars. For example, in many endoparasitic Hymenoptera first instar has a large head and jaws, though the later instars are maggot like.