Those who are afraid of creepy crawlies have it easy these days. Travel back 300 million years and you'll find a swarm of terrifying arthropods.
The spooky season is here! To commemorate the most wonderful scary time of the year. Will you be able to withstand the Terrifying Fossils?
If you're afraid of bugs, spiders, scorpions, or other creepy crawlies, now is the time to get away.
If you want to learn about Earth's creepy past, look no further.
Creepy Crawlers are... creepy. Although they are important components of nature's ecosystems, the mere presence of spiders and millipedes is enough to make even the most daring and fearless people's skin crawl. I, too, have had my fair share of insect encounters; earwigs seem to have a natural ability to frighten me even at the "best" of times. While modern insects are constrained by their small stature, some prehistoric insects were not. The insects of the Carboniferous period, which lasted from 359 to 299 million years ago and predated the dinosaurs, grew to truly ungodly proportions.
Life-sized replica of Arthropleura
By "ungodly," I mean frighteningly large to the point of becoming nightmare fuel. Let's begin with the enigmatic Carboniferous insect Arthropleura. I say "insect" because it's unclear whether Arthropleura was a millipede or a centipede from the fossilized remains, which consist mostly of trackways and the occasional exoskeletal plate, making it difficult to place it in either family. One thing is painfully clear: it is enormous. Arthropleura, at two metres long[iii], dwarfs even the largest of its modern ancestors by more than 1.5 metres and is the largest terrestrial arthropod of all time. Fortunately, Arthropleura was a vegetarian, but it would have been a terrifying sight.
In the Carboniferous, Arthropleura was not alone. Meganeura, or giant dragonflies, were among the first animals to learn to fly, with wingspans reaching 70 cm (over two feet). 70-centimeter scorpions stalked the land, snacking on early reptiles and smaller insects that were three times the size of their ancestors. While it was thought that giant spiders known as Megarachne lived in the Carboniferous period, spiders were only beginning their evolutionary process at the time. Megarachne, on the other hand, represents one of the last Eurypterids, or "sea-scorpions," animals that could grow to over 2.5 metres in length at their apex but were only about one metre in length by the Carboniferous and Megarachne. Their diminution in size did not prevent them from being creepy; Megarachne, in my opinion, resembles the face-huggers from the Aliens franchise.
With such a large cast of giant creepy-crawlies, one must wonder: how did they get so big? First and foremost, they had plenty of oxygen. Insects do not have lungs and instead absorb oxygen through spiracles in their skin and circulate it through trachea tubes. As a result, their size is limited by the amount of oxygen they can absorb from their surroundings. While the oxygen content of the Earth today is about 21%, it may have been as high as 35% during the Carboniferous period. The Carboniferous set the stage for exceptional growth in insects and arthropods due to its high oxygen levels.
The other factor driving their meteoric rise is much simpler: a lack of competition. Life was just starting to spread onto land during the Carboniferous period. Large carnivorous amphibians were restricted to Carboniferous swamps, reptiles were in their early stages of evolution, and mammals, birds, and dinosaurs had not yet evolved. There was no competition on the land, so insects and arachnids could grow to enormous proportions. This, combined with higher oxygen levels, aided in the growth of some truly monstrous bugs.
It's worth noting that not all insects were massive during the Carboniferous period. There were still animals that resembled millipedes, scorpions, and other animals that we see today. These smaller animals were better prepared for the dramatic climate change that occurred at the end of the Carboniferous period, reducing the amount of oxygen in the atmosphere and causing the vast swamp systems that the giant insects called home to decline. Such changes, combined with the emergence of terrestrial amphibians and reptiles, would spell the end of the giant insect. While I would love to see 2-meter millipedes and dog-sized scorpions, I am sure many people are relieved that they are no longer alive.
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