While many insects today are relatively small, Earth’s ancient past was home to truly colossal arthropods. Exploring these prehistoric giants offers a glimpse into a time when conditions allowed for life forms that dwarfed their modern counterparts.
The Reigning Ancient Giant
The largest insect known to have ever lived is Meganeuropsis permiana, a prehistoric creature often referred to as a griffinfly. This formidable insect, a distant relative of modern dragonflies, soared through the skies during the Permian period, approximately 285 to 290 million years ago. Its most striking feature was an impressive wingspan that could reach up to 75 centimeters (about 2.5 feet), making it comparable in size to some modern birds.
Beyond its massive wings, Meganeuropsis permiana also had a substantial body, estimated to be up to 47 centimeters (18.5 inches) long. This predatory insect likely used its large compound eyes and powerful mandibles to hunt other insects and even small vertebrates, such as amphibians and early reptiles. Fossil evidence of this ancient giant has been discovered in various locations, including Kansas in the United States, as well as parts of China, Russia, and France.
Other Notable Prehistoric Arthropods
While Meganeuropsis permiana holds the record for insects, other ancient arthropods also reached astonishing sizes. One such example is Arthropleura, a massive myriapod, which is a group that includes modern millipedes and centipedes, rather than a true insect. This creature was the largest known land arthropod of all time, with some individuals estimated to be over 2.5 meters (8 feet) long and weighing as much as a large dog. Arthropleura lived from the Carboniferous to the early Permian periods, roughly 344 to 292 million years ago, and was a herbivore, feeding on decaying plant matter.
Another notable insect from prehistoric times is Meganeura monyi, a slightly older griffinfly from the Late Carboniferous period, around 300 million years ago. This species also boasted an immense wingspan, typically ranging from 65 to 75 centimeters. Similar to its later relative, Meganeura monyi was a predator, likely preying on other insects. Additionally, fossil records show that ancient cockroaches, known as roachoids, were significantly larger than most modern species, with some reaching lengths of up to 9 centimeters (3.5 inches) around 300 million years ago.
Why Ancient Insects Grew So Large
The immense size of many prehistoric insects is primarily attributed to higher levels of atmospheric oxygen during the Paleozoic Era, particularly the Carboniferous and Permian periods. During these times, oxygen concentrations in the air are estimated to have been as high as 30% to 35%, significantly greater than today’s approximately 21%. Insects do not possess lungs; instead, they breathe through a system of tubes called tracheae that deliver oxygen directly to their tissues via diffusion.
This tracheal respiratory system is a limiting factor for insect size, as oxygen diffusion becomes less efficient over longer distances. With a higher oxygen concentration in the ancient atmosphere, oxygen could more effectively diffuse throughout a larger body, overcoming this physiological constraint. Another contributing factor was the relative absence of large aerial vertebrate predators, such as birds and bats, which allowed flying insects to evolve to greater sizes without constant predatory pressure.
Comparing to Today’s Largest Insects
Today’s insects, while diverse, do not reach the colossal proportions of their ancient ancestors. The largest living insects are measured by different criteria, such as length, weight, or wingspan. For instance, the giant Chinese stick insect (Phryganistria chinensis) holds the record for the longest insect, with some specimens measuring over 60 centimeters (2 feet) including outstretched legs.
In terms of weight, the larval stage of the Goliath beetle (Goliathus goliatus) can exceed 100 grams, while the adult female Giant Weta (Deinacrida heteracantha) of New Zealand can weigh up to 71 grams. For wingspan, the Queen Alexandra’s birdwing butterfly (Ornithoptera alexandrae) can have a wingspan of up to 30 centimeters (12 inches).
These modern giants are considerably smaller than their prehistoric counterparts. This is largely because current atmospheric oxygen levels are lower, and the presence of numerous vertebrate predators like birds and bats exerts evolutionary pressure, favoring smaller, more agile body forms.