How has the small size of insects contributed to their success?

Their small size and ability to fly permits escape from enemies and dispersal to new environments. Because they are small they require only small amounts of food and can exist in very small niches or spaces. In addition, insects can produce large numbers of offspring relatively quickly.

Smallest Insects. For an animal with an exoskeleton, small size is a distinct advantage. If insects were as large as cows or elephants, their exoskeleton would have to be proportionately thicker to support the additional mass of body tissue. But a thicker exoskeleton would also be heavier and more cumbersome.