Long before birds ruled the sky, a giant dragonfly-like beast earned the title of being the largest known insect of all time. Known as Meganeuropsis permiana, this extinct bug had an estimated wingspan of 71 centimeters (28 inches), around the size of a well-fed pigeon.
Remains of Meganeuropsis permiana suggested it looked a lot like the dragonflies of today, although they aren’t categorized as true dragonflies. Instead, they belong to an extinct order of insects known as Meganisoptera, aka griffinflies.
They lived during the late Permian era around 275 million years ago when the Earth looked like very different compared to today. All of the planet’s major landmasses were collected into a single supercontinent known as Pangaea, formed after Euramerica and Gondwana collided. While the land was largely dominated by reptiles, insects underwent a dramatic increase in diversification at this time.
Meganeuropsis is a genus of insect that's split into two species. The larger Meganeuropsis permiana was first described by American entomologist and paleontologist Frank Carpenter in 1939 based on a single incomplete specimen found in Elmo, Kansas. A few years later, he described a similar yet smaller species, Meganeuropsis americana.
As you can probably tell by this scant evidence, it’s extremely difficult to discover specimens of these insects. Since insects do not have bones, they do not fossilize the same way animals like mammals, fish, birds, and reptiles.
There is a theoretical limit to how big an insect can grow – and it seems that Meganeuropsis permiana was knocking on the door of that threshold.
Firstly, they are limited by their exoskeleton. Insects molt their exoskeleton as they grow, which can be a costly process. The larger an insect becomes, the more energy and resources it needs to produce a new, larger exoskeleton.
Secondly, insects breathe in a totally different way from birds, reptiles, and mammals. They breathe air through a system of tiny tubes called tracheae that deliver oxygen directly to their cells. As an insect grows larger, the air-filled tubes become less efficient in supplying oxygen to all of its cells. Insects also have a relatively simple metabolic system, which doesn’t cope well with maintaining a larger body size.
Some similar animals can bend these rules, however. Arthropleura was the largest millipede to have ever scuttled across Earth, measuring around 2 meters (6.6 feet) long and half a meter (1.6 feet) wide. They are not classified as insects though, as they are not part of the Insecta class and belong to their own class called Diplopoda.
This taxonomic quirk leaves the record for Earth's largest-known insect firmly in the claws of Meganeuropsis permiana.