On hatching from eggs of the insects do not resemble their parents. To attain the maturity and to become adults, these young ones have to pass through different stages of development assuming distinctly different morphological forms. These morphological forms may not be similar to their parents. Thus, morphological forms may not be similar to their parents. Thus, the conspicuous changes inform and appearance assumed by the insects between hatching and maturity is called metamorphosis. This is a characteristic phenomenon in the life of majority of winged insects. Exceptions however, do occur in the primitive or primarily wingless and secondarily wingless insects. The group of such insects, which do not undergo metamorphosis, is called Ametabola. In this group the development of insects occurs through three stages viz., egg, young ones and adult. The young one looks like their parents in its all body characters. The only difference between young ones and adults is that the young one are smaller in size and shape while the adults possess functional reproductive organs. In this group of insects neither the young ones nor the adult’s stages show any presence of even rudiments of wings in the course of development and in their ancestral development. They are therefore; called primarily, wingless insects e.g. Silver fish, Spring tails, Compodea, Proturans etc.
The growth of an insect is a continuous process while the integument or body wall of an insect forming the exoskeleton is rigid and it is only possible of insect to put on growth by casing off the old cuticle periodically. This process of periodical shedding of old cuticle is called ecdysis or moulting and old skin cast off by insect is called exuviae. The form attained by the insect between two successive moulting is called instars. There are several such instars in the immature stage of insects. (4 to 8 moults) the total period between any two moulting is called a stadium.
Significance of Metamorphosis:
1. It helps the insects to tie over unfavorable climatic conditions by entering into hibernation, aestivation and or diapauses.
2. It helps the insects to accommodate growth by periodical shedding of their old cuticle and by formation of new cuticle.
3. It helps the insects to reduce or avoid competition for food amongst themselves by either entering into inactive stage or by acquiring different feeding habits & habitats.
4. It helps the insects as a protective adaptation by way of camouflaged/mimicry i.e. resemblance to the nature.
5. It also serves as important aspect in classification of insects.