When we think of insects today, we typically imagine small creatures that we can easily swat away or that scurry underfoot. However, during prehistoric times, particularly in the late Paleozoic and early Mesozoic eras, Earth was home to insects of truly monstrous proportions. These creatures weren’t just slightly larger than their modern counterparts—many rivaled modern birds in size. This fascinating chapter of Earth’s history, when arthropods reached gigantic proportions, was made possible by specific environmental conditions including higher oxygen levels in the atmosphere and the absence of certain predators. Let’s explore ten remarkable prehistoric insects that would have made today’s entomologists stare in amazement, and perhaps relief that they’re no longer buzzing around our planet.
Meganeura The Griffinfly Giant
Perhaps the most famous prehistoric insect, Meganeura was an enormous dragonfly-like creature that lived approximately 300 million years ago during the Carboniferous period. With a wingspan reaching up to 2.5 feet (75 cm), these insects were about the size of a modern hawk. Fossilized remains discovered in France in the 19th century revealed a predator that would have been a terrifying sight as it patrolled the prehistoric skies. Unlike modern dragonflies that appear delicate despite their predatory nature, Meganeura had robust bodies and powerful wings that allowed them to be agile aerial hunters.
Scientists believe Meganeura was able to reach such impressive dimensions due to the oxygen-rich atmosphere of the Carboniferous period, with oxygen levels reaching up to 35% compared to today’s 21%. This higher oxygen concentration allowed for more efficient respiration through their tracheal breathing system, overcoming the limitations that keep modern insects relatively small. These magnificent predators would have fed on other insects and possibly small amphibians, using their strong mandibles to capture prey mid-flight.
Meganeuropsis North America’s Aerial Giant
While Meganeura gets much of the attention, its relative Meganeuropsis actually holds the record for the largest insect ever discovered. Living approximately 275 million years ago during the Permian period, Meganeuropsis permiana had an astonishing wingspan of up to 2.6 feet (80 cm)—comparable to the wingspan of a modern crow. Fossil specimens of this North American giant were discovered in Oklahoma and Kansas, revealing an insect that dominated the skies of prehistoric North America much as its cousin Meganeura did in Europe.
Like other giant insects of its era, Meganeuropsis benefited from the oxygen-rich atmosphere, allowing it to overcome the respiratory limitations that constrain modern insect size. Its body structure was similar to modern dragonflies but vastly more robust, with powerful flight muscles and strong mandibles for capturing prey. The ecological role of these massive aerial predators would have been significant, helping to control populations of smaller flying insects in the prehistoric ecosystem.
Titanoptera The Predatory Cricket Giants
Moving into the Triassic period approximately 250-200 million years ago, we encounter the fearsome Titanoptera. These massive insects resembled crickets or katydids but evolved as specialized predators with powerful forearms similar to those of a modern mantis. With wingspans reaching up to 14 inches (36 cm), species like Gigatitan vulgaris would have been roughly the size of a small songbird. Their fossilized remains have been found primarily in Australia and Russia, indicating a wide distribution across the ancient supercontinent Pangaea.
Titanoptera possessed distinctive features including large, spined forelegs perfectly adapted for grasping prey. Unlike modern crickets that are primarily herbivorous, these giants were active predators that likely hunted smaller insects and possibly even small vertebrates. Their extinction coincided with the rise of early pterosaurs and other flying reptiles, suggesting possible competition for the aerial predator niche. The discovery of these creatures revealed an unexpected evolutionary branch where cricket-like insects developed predatory adaptations and reached sizes that would be unimaginable for their modern relatives.
Pulmonoscorpius The Bird-Sized Scorpion
While technically an arachnid rather than an insect, Pulmonoscorpius kirktonensis deserves mention for its extraordinary size. This Carboniferous scorpion grew to lengths of approximately 28 inches (70 cm)—about the size of a large hawk or eagle. Fossil specimens discovered in Scotland show a creature that would have been a formidable predator in both terrestrial and possibly aquatic environments. With massive pincers and a venomous stinger, Pulmonoscorpius would have been one of the most dangerous arthropods of its time.
Like many prehistoric arthropods, Pulmonoscorpius benefited from the oxygen-rich atmosphere of the Carboniferous period. Its large size would have allowed it to prey on a variety of smaller animals, including other arthropods and possibly small amphibians. The existence of such giant scorpions provides important insights into the evolutionary history of arachnids and the environmental conditions that allowed arthropods to reach such impressive dimensions. While modern scorpions can be intimidating, they pale in comparison to their prehistoric ancestors that roamed ancient forests and swamps.
Arthropleura The Colossal Millipede
Another remarkable arthropod that wasn’t technically an insect but deserves recognition for its bird-exceeding size was Arthropleura. This massive millipede-like creature lived during the Carboniferous and early Permian periods, approximately 315-295 million years ago. Growing to lengths of up to 8.5 feet (2.6 meters) and widths of over 1.5 feet (45 cm), Arthropleura was not just bird-sized—it was larger than many modern predatory mammals. Fossil trackways and body fragments discovered in Europe and North America have allowed scientists to reconstruct this gentle giant.
Despite its intimidating size, Arthropleura was likely herbivorous, feeding on the abundant plant matter in Carboniferous forests. Its many legs would have allowed it to navigate through dense undergrowth, while its robust exoskeleton provided protection against early amphibian predators. The extinction of Arthropleura coincided with declining oxygen levels and changing climate conditions at the end of the Carboniferous period, highlighting how dependent these giant arthropods were on specific environmental conditions. Imagining an encounter with this creature—a millipede longer than a human is tall—provides a vivid reminder of how alien Earth’s prehistoric ecosystems would appear to modern eyes.
Mazothairos The Giant Permian Mayfly
Mayflies today are known for their ephemeral adult lives, sometimes lasting only hours. Their prehistoric relatives, however, were far more imposing. Mazothairos, a giant mayfly from the Permian period approximately 270 million years ago, had a wingspan reaching up to 19 inches (45 cm)—comparable to that of a modern crow or small hawk. Fossil evidence of these massive insects has been found in Kansas, USA, revealing creatures that retained the basic body plan of modern mayflies but at a dramatically larger scale.
Like modern mayflies, Mazothairos likely spent most of its life as an aquatic nymph before emerging as a winged adult for a brief reproductive period. However, the sheer scale of these insects would have made their emergence a much more significant ecological event than that of their modern counterparts. When thousands of these massive insects took to the air simultaneously, as mayflies often do, it would have created a spectacle unlike anything in the modern world. Their size suggests they may have played important roles as both prey for larger predators and as consumers of significant amounts of organic matter during their aquatic nymph stage.
Apthoroblattina The Giant Permian Cockroach
Cockroaches are among the most successful insect groups, having survived for over 300 million years with relatively little change to their basic body plan. Their prehistoric relatives, however, were considerably larger than modern species. Apthoroblattina, a giant cockroach from the Permian period approximately 270 million years ago, reached lengths of up to 6 inches (15 cm) with a substantial wingspan—making it comparable in size to many modern songbirds. Fossil specimens discovered in various locations worldwide show that these insects were widespread before the Permian-Triassic extinction event.
Like their modern descendants, prehistoric cockroaches such as Apthoroblattina were likely scavengers and detritivores, helping to break down dead plant and animal matter in ancient ecosystems. Their large size would have allowed them to process significant amounts of organic material, making them important components of nutrient cycling in prehistoric forests. The resilience of the cockroach lineage through multiple mass extinction events attests to their adaptability, though modern cockroaches have never approached the impressive dimensions of their ancient ancestors. If you find modern cockroaches disturbing, imagine encountering one the size of a cardinal fluttering through a prehistoric forest!
Archaeorthoptera The Primitive Giant Locusts
During the Carboniferous and Permian periods, approximately 300-250 million years ago, enormous orthopterans (the group including grasshoppers, locusts, and crickets) roamed ancient landscapes. Archaeorthoptera represents a diverse group of these primitive giant “locusts” that reached sizes far exceeding their modern relatives. With wingspans of up to 12 inches (30 cm) and body lengths reaching 7 inches (18 cm), these insects were comparable in size to medium-sized birds like doves or pigeons. Fossils of these impressive creatures have been discovered across Europe, North America, and Asia.
Unlike the predatory Titanoptera mentioned earlier, many Archaeorthoptera species were likely herbivores, feeding on the abundant plant life of Carboniferous forests and swamps. Their powerful hind legs would have enabled impressive jumping capabilities, allowing them to escape predators and navigate complex vegetation. The existence of these giant herbivorous insects suggests they played important roles in prehistoric food webs, potentially serving as key primary consumers that transferred energy from plants to predators. Modern grasshoppers can cause significant crop damage during outbreaks; imagining swarms of their bird-sized ancestors gives new perspective on their potential ecological impact.
Stephanotypus The Giant Water Bug
Water bugs today include some of the largest modern insects, with certain species exceeding 4 inches in length. Their prehistoric relatives, however, were substantially larger. Stephanotypus, a giant water bug from the Permian period approximately 260 million years ago, reached lengths of up to 8.5 inches (21 cm) with robust bodies and powerful raptorial forelegs. Fossils discovered in Russia reveal predators that would have dominated ancient freshwater ecosystems, comparable in size to small wading birds like sandpipers.
Like modern water bugs, Stephanotypus was an ambush predator that likely fed on aquatic invertebrates, small fish, and amphibians. Their powerful front legs would have allowed them to grasp prey, while their beak-like mouthparts could inject digestive enzymes and suck out liquefied tissues. As top predators in ancient ponds and streams, these giant water bugs would have had significant impacts on aquatic community structure. Modern water bugs are known for their painful bites; their prehistoric relatives would have been capable of inflicting much more serious wounds with their larger size and more powerful forelegs.
Cretophasmomima The Giant Permian Stick Insect
Stick insects today are known for their remarkable camouflage and elongated bodies. During the Permian period, approximately 250 million years ago, stick insects like Cretophasmomima reached truly impressive proportions. With body lengths exceeding 16 inches (40 cm) and substantial wingspans, these insects were comparable in size to many modern birds. Fossil evidence from China and Eastern Europe has revealed these giants that blended into the ancient forest canopy just as their smaller modern relatives do today.
The gigantic size of Cretophasmomima would have enhanced its camouflage capabilities, allowing it to effectively mimic branches of Permian trees and ferns. Like modern stick insects, they were likely herbivores that fed on foliage while relying on their camouflage to avoid predation. Their existence demonstrates that the distinctive stick insect body plan evolved early in insect evolution and has remained successful for hundreds of millions of years, albeit at a much reduced scale in the modern era. The thought of a stick insect larger than a modern falcon provides a striking image of the unique megafauna that characterized Earth’s prehistoric insect communities.
Why Prehistoric Insects Grew So Large
The phenomenon of gigantism in prehistoric insects has fascinated scientists for generations, leading to several compelling theories about the conditions that allowed for such extraordinary growth. The most widely accepted explanation involves atmospheric oxygen levels, which reached up to 35% during the Carboniferous period compared to today’s 21%. Insects breathe through a system of tubes called tracheae that deliver oxygen directly to tissues without using blood as a carrier. This system becomes less efficient as body size increases, essentially limiting how large an insect can grow. Higher oxygen concentrations would have allowed oxygen to diffuse more efficiently through the tracheal system, effectively removing this size constraint.
Additionally, the absence of certain predators likely contributed to insect gigantism. Birds, which are major insect predators today, hadn’t yet evolved during the Carboniferous and Permian periods when many giant insects thrived. The first birds appeared in the Jurassic period, long after the heyday of giant insects. The decline in insect size coincides with the evolution and diversification of birds and other flying vertebrates, suggesting that predation pressure may have selected for smaller insect body sizes. Modern research on island gigantism, where animals isolated from predators often evolve larger sizes, supports this theory. Climate factors, including higher global temperatures and humidity levels during certain prehistoric periods, may have also played supporting roles in allowing arthropods to reach such impressive dimensions.
A World of Giants Lost to Time
The prehistoric insects we’ve explored represent a fascinating chapter in Earth’s evolutionary history that has no modern parallel. These bird-sized arthropods thrived in conditions vastly different from today’s world, dominating ecosystems long before the rise of mammals and birds. Their existence challenges our perception of insects as necessarily small creatures and provides valuable insights into how environmental conditions shape evolutionary possibilities. The oxygen-rich atmosphere of the Carboniferous and Permian periods created a unique window of opportunity for arthropods to reach dimensions impossible under current atmospheric conditions.
As our planet’s atmosphere changed and new predators evolved, these giants gradually disappeared, leaving only their smaller descendants and fossilized remains as evidence of their existence. Modern insects, while impressive in their diversity and ecological importance, represent a scaled-down version of their prehistoric ancestors. Studying these ancient giants not only satisfies our curiosity about Earth’s past but also helps scientists understand the complex relationships between atmosphere, physiology, and evolutionary constraints. The next time you encounter a dragonfly or cockroach, take a moment to imagine its ancient relative—a creature that might have been large enough to look you in the eye—and appreciate how dramatically Earth’s insect fauna has changed over hundreds of millions of years.
As a little kid, I fell in love with nature, wildlife, and animals. Living in the USA, South Africa, Italy, China and Germany gave me the opportunity to discover the world's Wildlife. My favorite animals are Mountain Gorillas, Siberian Tigers, and Great White Sharks.
I'm a certified PADI Open Water Diver, went to Everest Base Camp and Trekked Gorillas in Uganda. I hold a Master of Science in Economics and Finance.
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