Hi
The term metamorphosis means the changes that occur in the body structure and general habits of insects from the time they are born to the time they mature. Metamorphosis can be complete or incomplete and below are their main differences:
1: In complete metamorphosis there are four stages through which the body structure of an insect goes through i.e Egg, Larva, Pupa and Adult. On the other hand, in Incomplete metamorphosis there are three stages through which the body structure of an insect goes through i.e Egg, nymph, Adult.
2: During complete metamophosis, the second stage of insect is larva which is a very active form that eats rigorously, on the other hand in incomplete metamorphosis, the second stage consists of nymph that is a almost an adult and is in more developed form as compared to the former's larva and pupa.
3: Complete metamophosis occurs in fleas, ants and wasps while incomplete metamorphosis happens in cockroaches, praying mantis and termites.
Hope it helps!