Theories explain phenomena, whilst laws are generalizations which characterize them.
Answer:
It is believed that insects are so successful because they have a protective shell or exoskeleton, they are small, and they can fly. Their small size and ability to fly permits escape from enemies and dispersal to new environments. ... In addition, insects can produce large numbers of offspring relatively quickly.
I believe that it's Bilateral symmetry. Hope it's right. :)
see image hope it helps you
