The Earth’s largest phylum is Arthropoda, including centipedes, millipedes, crustaceans, and insects. Insects are the largest and most successful class of animals on Earth. This success, zoologists believe, is attributed from certain biological traits such as their small size or ability to fly for some (Postlethwait & Hopson, 2010). The exoskeleton of most insects supports them inside but also protects them from outside. John Meyer, professor at NCSU, explains as a “suit of armor”, the exoskeleton can resist both physical and chemical attack (2007). He also covers how their small size allows them to hide, flight allows them to escape, high fertility and high fecundity allows for a large reproductive potential, metamorphosis promotes survival, and their ability to adapt easily (2007). All these characteristics listed above amongst several others are the reason why insects are the most successful animals on earth. In many science fiction scenarios, post-apocalyptic Earth is mainly populated with giant insects.
There are many theories as to why giant ants and moths don’t rule the world. Janet Fang’s research found that it was a chemical balance in hormones that prevent growth. She stated “Two mechanisms determine how big an animal gets: One controls growth rate, the other controls growth duration. The first commands how fast an animal grows and depends on insulin and similar hormones that prompt cells to divide and multiply. The latter regulates the timing of maturation using developmental hormones (like androgens and estrogens in people).” (Fang, 2014) There is also the common sense characteristics that would prevent growth such as their limiting exoskeleton or the lack of lungs to breathe enough oxygen because their trachea would not be able to process enough for a larger body to survive.
Postlethwait, J., & Hopson, J. (2010). Life (Student ed., pp. 244-245). Belmont, CA: Cengage Learning. Meyer, J. (2007, January 21). Reasons for Success. Retrieved February 2, 2015, from http://www.cals.ncsu.edu/course/ent425/text01/success.html Fang, J. (2014, May 15). Why Monstrously Large Insects And Spiders Don’t Exist. Retrieved February 2, 2015, from