Why Don’t Giant Bugs Exist Today?

Why Don’t Giant Bugs Exist Today?

Giants of the Past

With a wingspan of 2 feet (65cm), the Meganeura Dragonfly used to roam the skies three hundred million years ago. These prehistoric dragonflies were the size of hawks and had a predatory nature, swopping in and capturing prey to devour. It sounds straight out of a horror film, but they were, at one time, real. Today, the largest insects in existence include the Giant Weta (11cm), the Goliath Beetle (12cm), and the Titan Beetle (16.5cm), to name a few. Moreover, the average modern dragonfly has a wingspan of only 10cm – these are all a far step from their prehistoric ancestors… but why? What happened that made insects reduce in size so drastically?

Theory 1 – The Exoskeleton

While humans and animals carry their skeletons on the inside, insects are rather unique, bearing exoskeletons. This means that their shells/the outer layer of their bodies, are, in fact, their skeletons. For a long time, it’s been speculated that the larger an insect grows, the heavier their exoskeleton would be, therefore limiting the creature’s ability to grow beyond a certain size. In truth, however, there is very limited data backing up this hypothesis and, out of the data that does exist, the facts do not strongly support this theory.

Theory 2 – Oxygen

Not only do insects have very different skeletal structures than humans and animals, they also breathe in a very different way. Insects posses a series of holes along the length of their bodies that take oxygen into inner tubes called tracheoles. Tracheoles spread throughout the body, getting as small as a micron in size in order to diffuse oxygen on a cellular level throughout the insect. Dr. Jon Harrison, entomologist at Arizona State University states that this very phenomenon could be the limiting factor in the size of insects. The larger the insect, the longer the canals of tracheoles would have to be, making it substantially more difficult to properly disperse oxygen throughout the insect’s body. But then why were there large insects in the past? Clearly it wasn’t problematic at one point.

The Paleozoic Atmosphere

The percentage of oxygen in our atmosphere today is roughly 21%. This was not the case in the past, however. Geologists conducted a study in which it was discovered that in the late Paleozoic Era, the percentage of oxygen in the atmosphere rose to at least 32% oxygen. This eliminates the problems with tracheoles, allowing the larger bugs to breathe with ease due to the plethora of oxygen in the atmosphere at the time. This is just a theory, however.

Dr. Harrison states that we don’t have any definitive answers yet as to why large insects no longer exist, but that this is the most convincing theory so far. Regardless, we can probably all agree that, whatever the case is, we are glad that they don’t exist today… bugs are big enough as it is.


Nelson, B. (2013) These Are the 10 Biggest Bugs in the World, Business Insider. Mother Nature

Network. Available at: https://www.businessinsider.com/10-of-the-biggest-bugs-in-the-world-2013-12 (Accessed: May 2020).

Painter, D. (N/A) Big Big Bugs, Arizona State University. Available at:

https://askabiologist.asu.edu/explore/prehistoric-insects (Accessed: May 2020).

The Largest Complete Insect Wing Ever Found (2007) Harvard Magazine. Available at:

https://harvardmagazine.com/2007/11/dragonfly-html (Accessed: May 2020).

Titan Beetle (2011) The Smithsonian Institute. Available at:

https://www.si.edu/newsdesk/snapshot/titan-beetle (Accessed: May 2020).

Why Aren’t There Giant Insects? (2012) SciShow. Available at:

https://www.youtube.com/watch?v=179FuGuk1qE&list=PLB3FCEEAC84884760&index=50 (Accessed: May 2020).  

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