About 300 million years ago, insects were scales larger than they are today: a shudder-inducing thought for anyone with entomophobia. Griffinflies, for instance, were massive dragonflies with wingspans reaching 28 inches. Insects were able to reach gargantuan sizes largely because the earth's atmosphere was rich in oxygen in prehistoric times. Since then, as oxygen levels have decreased, insects' air pipes have shrunk to adapt, and their bodies along with them.

However, there are still many species around the world that have maintained impressive sizes. They are mostly found in oxygen-rich and scarcely populated areas, such as rainforests, that have allowed them to evolve without intrusion.

"Biggest" Can be Complicated

Stacker compiled a list of 20 of the biggest insects in the world using various news, scientific, and other sources. However, defining "biggest" can be more complicated than it seems. For instance, the insect with the largest wingspan is Queen Alexandra's birdwing, which can stretch to an entire foot in width. The longest or tallest insect would be Phyrganistria chinensis Zhao, a stick insect that can grow to 24.6 inches. The heaviest insect is the Giant wētā, weighing up to 70 grams.

Tanawat Palee // Shutterstock
Tanawat Palee // Shutterstock

By all units of measurement, beetles and moths tend to be found in larger sizes more often than other insects. Read on to find out just how big these impressive creatures can get and what that means for their diets, habitats, and defenses.

LOOK: 20 of the biggest insects in the world

Stacker compiled a list of 20 of the biggest insects in the world using a variety of news, scientific, and other sources.

More From 99.1 WFMK