Generally, all insects have four wings, but they are not always used for flying.
Flies in particular are also among the best flyers, and yet, they use only two of their wings for flying, the other two shrank to became halteres, a sensory organ acting like a gyroscope.
Dragonflies may be the best fliers in the insect world thanks to their four independently controlled wings, but flies may be the second best, and they achieved that by losing two of their four wings. Evolution is interesting.
Another example of evolution deleting something instead of creating something. It is bizarre how many examples that people cite demonstrating evolution are actually demonstrating devolution.
insects are so different from vertebrates (e.g. multi compartment bodies thanks to how they express the HOX gene) that the flying strategies are also quite different.
At the current level of O2 in the air I don't believe that flying insects can grow as large as even a hummingbird, much less an eagle.
The insect grows up to 7 cm in length whereas the bird can stay less than 6 cm at adulthood. No information about the insect weight though (for a proper comparison).
