Were Bugs Bigger When Dinosaurs Existed?

Bugs reached incredible lengths when the dinosaurs roamed Earth. However, most shrunk after oxygen levels in the air decreased at the end of the Permian period.

Sep 18, 2023By Colt Dodd
were bugs bigger when dinosaurs existed

When someone bemoans seeing a giant insect, they’re generally referring to a cockroach or a freakishly long centipede. If they lived alongside dinosaurs about 300 million years ago, they would probably have to redefine what constitutes a big bug.

Some species of bugs were bigger when dinosaurs roamed the earth, with some boasting three-foot-long wingspans. That’s the same size as a small child! Yet, a lot has changed since the land before time; many of these large insects went extinct or evolved into smaller versions of themselves.

Bugs Were Bigger When Dinosaurs Existed

Meganeuropsis Permiana model with  scientist
Image Credit: Wikimedia Commons

Today, modern dragonflies don’t get longer than five inches. This makes them a welcome sight in many gardens and outdoor spaces. Yet, its distant relative makes them seem microscopic in comparison.

Meet Meganeuropsis Permiana. According to the University of Nebraska-Lincoln, these massive insects lived during the late Permian period, which was about 275 million years ago. They had a wingspan of 2.5 feet and weighed one pound––the same as a crow.

So, what happened to Meganeuropsis Permiana? Well, at the end of the Permian period, a series of intense volcanic eruptions in Siberia caused what’s known as the “Great Dying.” This led to the mass extinction of more than half of all living creatures. It resulted in the death of 96 percent of marine life and proved more catastrophic than the extinction of the dinosaurs.

Why Were Prehistoric Bugs Bigger?

rendering of a Meganeuropsis Permiana
Image Credit: Wikimedia Commons

There are two main reasons why prehistoric bugs were so massive:

Little Competition

When large bugs roamed the earth, dinosaurs had not reached their full potential. Without pterodactyls and Archaeopteryx commanding the skies, they could easily feed on smaller insects without fear of being chow themselves. They also didn’t have to worry about predators eating their eggs.

Way More Oxygen

Take a deep breath. Pretty good, right? That’s because the Earth’s atmosphere is 21 percent oxygen. Per NASA, other gases include nitrogen, neon, carbon dioxide, and “other stuff.” It’s perfect for human life.

Back during the Permian period, however, the air was 31 to 35 percent oxygen. Now, oxygen levels are very important for insects since they don’t have lungs. So, the higher concentration of oxygen in the air, the larger they become.

After the Great Dying, the Earth’s atmosphere changed, delivering less oxygen to these mammoth moths. However, this was a gradual change that took place over thousands of years. It also coincided with the evolution of birds, and eventually, each species found its niche. Isn’t it fascinating how nature balances itself out?

What Were Some Giant Prehistoric Bugs?

dinosaurs in the permian period
Image Credit: Wikimedia Commons

As noted, the Meganeuropsis Permiana was one of the largest insects to ever grace Planet Earth. However, it wasn’t the only one. Other giant prehistoric bugs include:

  • Megarachne. Afraid of the bug that lives in the bathroom? Some species of megarachne (literally meaning “big spider”) could reach one foot in length. Imagine having a spider in the bathroom the size of a football!
  • Pulmonoscorpius. As if scorpions weren’t big enough! These critters lived more than 400 years ago and could reach more than two feet in length. Today’s biggest scorpion, commonly called the “giant forest scorpion,” usually doesn’t reach more than 10 inches long.
  • Arthropleura. This was one of the longest arthropods to ever roam the earth, with some specimens ranging more than six feet long. Its distant relative, the giant African millipede, measures just over a foot.

Very little is known about these creatures. However, scientists believe that their eating habits weren’t too far off from today’s insects. For instance, despite their size, Arthropleura likely feasted on insects and plants, just like modern millipedes do. However, how long they lived and how many eggs they laid is still a mystery.

Why Did Mega Bugs Die Out?

giant prehistoric dragonfly on tree
Image Credit: Wikimedia Commons

As noted, many insects went extinct at the end of the Permian period. Yet, other possible reasons for extinction include:

Too Much Competition After Dinosaurs Arrived

The large insects that survived the Great Dying had to deal with the dinosaurs that started appearing shortly after. One of those dinosaurs was the Archaeopteryx, the earliest known bird. It was faster and more agile than these monstrously sized bugs. Large insects were unable to compete with the new species for food and died out.

Their Habitats Changed

The Great Dying was no laughing matter. Volcanic activity from all over the globe spewed harmful gases into the air, snuffing out many life forms. When the dust settled, so to speak, food chains collapsed, and mega bugs that didn’t get suffocated starved instead.

Bugs Weren’t the Only Massive Prehistoric Creatures

fossil of a giant prehistoric dragonfly
Image Credit: Wikimedia Commons

Insects like the Meganeuropsis Permiana weren’t the only organisms to benefit from low competition and high oxygen levels. Here are some other massive ancestors of modern-day animals:

  • Woolly mammoths. Asian elephants are the closest relative to the woolly mammoth. Asian elephants weigh anywhere from four to five tons. Woolly mammoths had much stockier builds, easily weighing six to eight tons.
  • Ground sloths. Today’s two-toed sloth is generally 20 inches long––the same as a newborn baby. Ground sloths, on the other hand, were 20 feet long––the same as two sedans put end-by-end.
  • Titanoboa. Today’s green anaconda can reach 30 feet long. That’s nothing compared to the Titanoboa; these extinct serpents could measure more than 40 feet and weigh 2.5 tons!

The Great Dying didn’t take out these creatures. Instead, scientists believe that a mix of climate change coupled with human hunting took their toll. Despite the sheer size of these animals, they were no match for nature’s most vicious predator: man.

Could Bugs Get Huge Again in the Future?

prehistoric giant dragonfly on a log
Image Credit: Wikimedia Commons

Everything on Earth is cyclical. So, bugs could theoretically get bigger with the passage of time. However, many things would have to take place first. For instance, the atmosphere’s oxygen level would have to rise significantly. This in and of itself would kill off most life on Earth. Then, if some insects survive, they would have to reestablish their niches, find new prey, and even find new habitats.

So, will someone wake up with a three-foot-long dragonfly outside their bedroom window tomorrow? Probably not. Could they be millions of years from now? Who knows? Maybe.

Colt Dodd
By Colt Dodd

Colt Dodd is a sighthound enthusiast with three years of freelance writing experience. He has an Italian greyhound/Shetland sheepdog mix named Homer. In his spare time, he enjoys going to dog parks and writing fiction.