If you want to survive, it helps to be flexible. Eat what's available, time your bodily cycles to local conditions and don't put all of your eggs in one ecological basket. As a class, insects are masters of flexibility, both in terms of genetic adaptation and phenotypic plasticity — the way one set of genes can produce physical traits that vary in response to diverse environments [source: Whitman and Agrawal].
Insects account for nearly 73 percent of all known animal species and for almost 85 percent of land animal species. So far, we've found and named around 900,000 species, divided into 32 orders. Experts estimate that the true number could reach much higher, in the range of 2-30 million [sources: Danforth, Smithsonian]. The larger estimate derives in part from the amazing variety of insects that dwell in South American forest canopies [source: Smithsonian].
Their wide ranges of physical and social traits, and their notable adaptability, enable insects to spread into nearly every open niche. It also partly explains why insects survive mass extinctions [source: Yeates]. But even creatures as flexible as insects require a lot of time to radiate into so many wondrous forms.