Giant millipedes can grow to truly impressive sizes. Some species, such as the African Giant Black Millipede can reach lengths of 15 inches long. But millions of years ago, in Earth’s ancient past, there lived an even larger prehistoric millipede. Much larger.

Arthropleura the Largest Millipede of all Time

Hundreds of millions of years ago, in mysterious, primordial forests a truly giant millipede known as Arthropleura roamed the undergrowth. This colossal creature grew to lengths of around 8 feet long (and possibly even larger) and about 1.5 feet wide. This makes it the biggest terrestrial arthropod to have ever lived on Earth, as well as the largest land invertebrate.

Like today’s modern living millipedes, Arthropleura is believed to have been a herbivore, and not predatory. Fossilized parts of ancient ferns and their spores have been found preserved in the guts of some Arthropleura fossil specimens, suggesting it fed largely on dead ferns on the forest floor.

The closest living relatives to this gigantic creature are somewhat surprisingly believed to be the smaller Flat Millipedes, rather than the various species of larger, giant millipedes more commonly kept as pets today, such as the Giant African Millipede.

The body of Arthropleura was covered by segmented plates of relatively thin armor. Each segment of its body had three plates. There was one plate on top, and another one on each side.

At the time it lived, there were few large land animals. In fact, it was likely among the largest land animal around for much of its existence. Because of this, it had no known predators and was likely able to stroll through the ancient forests as it pleased with nothing to oppose it.

The Carboniferous Period

Arthropleura lived long before the time of the dinosaurs, from about 345 to 295 million years ago during the Carboniferous and early Permian periods. It lived in what is now the Northeastern US and Canada, as well as Scotland. At this time in the planet’s ancient past, North America and Europe were joined together in a super continent called Laurasia, allowing various species of animals and plants to spread freely between them. The global climate was wetter, and massive forests covered most of the land surface.

This period of Earth’s history is also where most of the planet’s coal comes from (and is the reason it was named the Carboniferous). At the time, there wasn’t really anything that broke down or ate dead wood. When a tree died and fell over, it didn’t really decay like it would today. Instead, it basically just laid on the ground or sunk down into soft swamp soil. Over millions of years, the trees kept on pilling up and getting buried, and eventually started turning into coal, due to the intense pressure and heat they were under.

While those ancient trees and plants were alive though, they had a dramatic effect on the make-up of the Earth’s atmosphere. They released massive amounts of oxygen into the air, drastically altering the planet’s atmospheric composition. Today, the atmosphere is made up of around 20% oxygen, but during the Carboniferous period, it rose to as much as 35%.

That extra oxygen in the atmosphere is what allowed many arthropods, including Arthropleura to grow to such enormous sizes. Arthropods breathe through pores in their exoskeletons. This is one of the main limiting factors to how big they can grow, because the larger they get, the harder it is for them to take in enough oxygen. The more oxygen in the atmosphere, the easier it is for them to breath. Too much oxygen however can also be deadly to their small larvae, so it also may have been the case that they increased in size mainly to avoid dieing of oxygen toxicity while young.

These extreme oxygen conditions allowed arthropods of all types to grow to ridiculous sizes. In addition to Arthropleura there were also insects such as Meganeura, a giant dragonfly (and the largest insect to have ever lived), who was as big as a bird.

Eventually, as the continents continued to drift and global climatic conditions changed, the lush, wet, forests and swamps of the Carboniferous period gave way to the drier conditions of the Permian period. This shift in climate is likely what lead to the extinction of Arthropleura. It disappeared from the fossil record about 295 million years ago.

Arthropleura Fossils

There have been various fossils of Arthropleura found over the years in the US, Canada, and Scotland. So far though, none of the fossils have been complete specimens. Most of the fossils discovered have been of the creature’s armor plates, or a few segments of its body.

There have also been a number of “trace fossils” of Arthropleura unearthed, refereed to as trackways. These trackways are tracks of footprints made by its many feet as it walked across the ground of the ancient forests where it lived.

Since no complete Arthropleura fossil has yet to be found, paleontologists have had to make educated guesses at certain aspects of what it was like when it alive.

No fossils of the creature’s mouth have been discovered so far, which has led paleontologists to believe that that part of its body was likely made of material that was too soft to be likely to fossilize. This provides a clue supporting the idea that this animal was indeed a herbivore, since such soft jaws and mouth parts probably would not have been very effective for hunting.

Appearances in Media

Arthropleura has made a couple of different appearances in documentaries. It was featured in the BBC documentary series First Life and Walking with Monsters. It was also in the BBC series Prehistoric Park.

Arthropleura has also appeared in a few video games. It’s one of the many prehistoric creatures that appears in the action-survival game ARK: Survival Evolved, where the player is able to fight or attempt to tame them.

It also appears in a player-created mod for the building-survival game Minecraft called Fossils and Archeology, where the player can try to tame and breed them.