$4 science assignment fast simple and easy

The Earth’s largest phylum is Arthropoda, including centipedes, millipedes, crustaceans, and insects. The insects have shown to be a particularly successful class within the phylum. What biological characteristics have contributed to the success of insects? In many science fiction scenarios, post-apocalyptic Earth is mainly populated with giant insects. Why don’t we see giant insects today? 

Your assignment should be 250-500 words in length.