Carboniferous The Frightening Fossils

Halloween Special: How the Carboniferous Was Bugging Out

For those afraid of creepy-crawlies, you have it easy living today. Travel back 300 million years, and you’d find a whole host of terrifying arthropods awaiting you.

Spooky season is upon us! To celebrate the most delightfully horrifying time of the year, Halloween themed articles will be released every Sunday on Max’s Blogosaurus for the rest of October. Will you be able to endure the Frightening Fossils?

If you are afraid of bugs, spiders, scorpions, or any other creepy-crawlies, this is probably the point where you should fly away.

If you’re in the mood to learn about earth’s creepy past, then look no further.

Creepy Crawlers are… well, creepy. Key components of nature’s ecosystems for sure, but the mere presence of things like spiders and millipedes is enough to make even the most daring, fearless people’s skin crawl. I too have had my fair share of encounters with insects; earwigs seem to have a natural ability to spook me at the “best” of times. While present-day insects are limited by their relatively small stature, some prehistoric insects had no such limits. In particular, the insects of the Carboniferous – a period before the dinosaurs that lasted from 359 to 299 million years ago[i] – grew to truly ungodly proportions.

Life-sized replica of Arthropleura

By “ungodly”, I of course mean terrifyingly large to the point of become nightmare fuel. Let’s start with the mysterious Carboniferous insect Arthropleura. I say “insect” because it is not clear whether Arthropleura was a millipede or a centipede, as fossilized remains consist only of trackways and the occasional exoskeletal plate[ii], making it hard to determine its relation to either family. One thing is painfully obvious: its enormous size. At two meters long[iii], Arthropleura dwarfs even the largest of its modern ancestors by over 1.5 meters and stands as the largest terrestrial arthropod of all time. Fortunately, Arthropleura was a vegetarian, though it still would have made for a frightening sight.

Arthropleura wasn’t alone in the Carboniferous either. Giant Dragonflies named Meganeura were among the first animals that learned to fly and had wingspans that reached 70 cm (over two feet) in length[iv][v]. 70-centimeter scorpions, animals that were over three times bigger than even their largest ancestors[vi], stalked the land and would have snacked on early reptiles and smaller insects. While it was believed that giant spiders named Megarachne also called the Carboniferous home, spiders were only beginning their evolutionary process at this time[vii]. Megarachne instead represents one of the last Eurypterids, or “sea-scorpions,” animals that at their apex could grow to over 2.5 meters in length, though by the Carboniferous and Megarachne, were only about one meter in length[viii]. Their reduction in size in didn’t stop them from being creepy, however; in my opinion, Megarachne looks like the face-huggers from the Aliens franchise.

With such a large cast of giant creepy-crawlies, the question must be asked: how on earth did they get so large? First, they had plenty of oxygen. Insects do not have lungs, and instead absorb oxygen through holes in their skin called spiracles and circulate oxygen in tubes known as trachea[ix]. Because of this, their size is somewhat limited by the amount of oxygen they can absorb from their environment. While Earth’s oxygen content today is about 21%, it may have been as high as 35% during the Carboniferous[x]. With such high oxygen levels, the Carboniferous set the stage for excelled growth in insects and arthropods.

KiaBugBoy on Twitter: "My first entry for a paleoart contest, thought I'd  depict the Carboniferous rainforest collapse #paleoart #digitalart  #paleontology #carboniferous #arthropleura #paleodictyoptera #insect  #treefern #lepidodendrales #art ...

The other factor for their giant growth is much simpler: a lack of competition. During the Carboniferous, life was only beginning to spread onto land. Large, carnivorous amphibians were restricted to the swamps of the Carboniferous, reptiles were in their earliest stages of evolution, and mammals, birds and dinosaurs hadn’t evolved yet. With no competition on the land, there was nothing preventing insects and arachnids from growing to massive sizes. This, in combination with increased oxygen levels, fostered the growth of some truly monstrous bugs.

I should note that not all insects were massive during the Carboniferous. There were still animals similar in size and appearance to the millipedes, scorpions, and others we live with today. These smaller animals were better equipped for the dramatic climate change that occurred at the end of the Carboniferous, reducing the amount of oxygen in the atmosphere, and causing a reduction to the vast swamp systems that the giant insects called home. Such changes, paired with the emergence of terrestrial amphibians and reptiles, would result in the giant insect’s downfall. While I would love to see 2-meter millipedes and dog sized scorpions, I am sure that many people take comfort in the fact that they are extinct.

…Or are they?

Just kidding.

…Or am I?

Happy Halloween!

Megarachne…and its movie contemporary


I do not take credit for any images found within this article.

Dragonfly header courtesy of Lucas Lima, found here

Carboniferous size chart courtesy of Emily Stepp, found here

Arthropleura found here

Carboniferous fire courtesy of Aldrich Kia on twitter, found here

Megarachne courtesy of unknown, found here

Facehugger found here

[i] “Carboniferous Period and Prehistoric Facts.” Science, National Geographic, 3 May 2021,  

[ii] Cochran, Ford. “Largest Land-Dwelling ‘Bug’ of All Time.” National Geographic Society Newsroom, 15 Dec. 2017,

[iii] Witton, Mark P., and Charles Robert Knight. Life through the Ages II: Twenty-First Century Visions of Prehistory. Indiana University Press, 2020.

[iv] Zielinski, Sarah. “14 Fun Facts about Dragonflies.”, Smithsonian Institution, 5 Oct. 2011,  

[v] Witton, Mark P., and Charles Robert Knight. Life through the Ages II: Twenty-First Century Visions of Prehistory. Indiana University Press, 2020.

[vi] Polis, Gary A. “Scorpion.” Encyclopædia Britannica, Encyclopædia Britannica, Inc.,  

[vii] Pappas, Stephanie. “305-Million-Year-Old ‘Almost Spider’ Unlocks Arachnid History.” Scientific American, Scientific American, 31 Mar. 2016,  

[viii] Black, Riley. “Megarachne, the Giant Spider That Wasn’t.” Science, National Geographic, 3 May 2021,

[ix] SLÁMA, KAREL. “A New Look at Insect Respiration.” The Biological Bulletin, vol. 175, no. 2, 1988, pp. 289–300.,

[x] Cochran, Ford. “Largest Land-Dwelling ‘Bug’ of All Time.” National Geographic Society Newsroom, 15 Dec. 2017,

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