It was 3 feet long, had pincers the size of your forearm, hunted on land and in water, and baffled scientists for 150 years. Now, they finally know what it was.
Picture a scorpion. Now make it a metre long, give it pincers the size of a large ruler, and drop it into the swamps of ancient Britain — 200 million years before the first dinosaur took its first step.
That is Praearcturus gigas. And scientists have just confirmed it is the largest scorpion that ever lived on Earth.
The prehistoric creature is estimated to have grown to lengths of around 3.3 feet — roughly 1 metre — and was equipped with formidable pincers measuring about 6.2 inches, or 16 centimetres long. To put that in perspective, the largest scorpion alive today, the emperor scorpion of West Africa, barely reaches 8 inches total. Praearcturus gigas was built on an entirely different scale.
The findings were published on June 2 in the journal Palaeontology.
A Mystery 150 Years in the Making
Remains of P. gigas, recovered from sites in England and Wales, were first documented in the 1870s. But researchers have long debated what kind of animal it actually was.
For over a century, the fossils confounded everyone who looked at them. Scientists initially suspected the remains represented a large woodlouse-like crustacean. Then in the 1980s, research suggested the fossils belonged to a scorpion — but that interpretation was subsequently challenged due to the fragmentary nature of the known remains and the absence of the characteristic scorpion tail.
The animal had been sitting in museum drawers, misidentified and misunderstood, for 150 years.
“Praearcturus has puzzled us palaeontologists for more than a century,” said Russell Garwood, a palaeontologist at the University of Manchester and co-author of the study.
How They Finally Cracked It
The breakthrough came when researchers at the Natural History Museum in London pulled out the old fossils and put them through modern imaging and analytical techniques — tools that simply did not exist when the fossils were first studied.
The team re-examined key specimens held in the NHM’s collections, compared them with other fossil material, and analysed recently described prehistoric animals that had been more confidently identified as scorpions. The analysis confirmed what the 1980s researchers had suspected: this was indeed a scorpion — and not just any scorpion. The world’s biggest.
“Confirming that this animal is a scorpion fundamentally changes our understanding of how and when these creatures evolved to such extraordinary sizes,” said study first author Richard Howard, curator of fossil arthropods at the Natural History Museum, London.
It Hunted in Water Too
Here is where the story gets even stranger. This giant was not purely a land predator.
Researchers suggest the creature may have been at least partially aquatic, based on the presence of flap-like structures in some of the fossils — similar to those which provide support and protection to the hard upper shells of lobsters and crabs.
“Without complex ecosystems to support Praearcturus on land, these animals probably spent part of their lives hunting in water,” Howard said.
This matters because 415 million years ago, the land was essentially empty. The scorpion stalked floodplains during the Early Devonian Period, when life on land was still in its relatively early stages and dominated by small arthropods. There were no forests. No large animals. Just small creeping things — and then this.
Why Was It So Enormous?
A semi-aquatic lifestyle could partly explain the scorpion’s greater size compared to its modern-day relatives, since water can support large bodies. But it may also reflect the relative lack of competition from other large terrestrial predators — potentially enabling it to reach sizes that would have been far more difficult to attain had rivals been present.
In short: nothing was big enough to stop it, so it just kept growing.
“What makes Praearcturus so interesting is that it became enormous at a time when life on land was otherwise very small. But it was a world that could somehow support a giant predator,” Garwood said.
Britain’s Forgotten Monster
It is a strange thought — that beneath the fields and coastlines of England and Wales lie the fossilised remains of what was once the most terrifying predator on the planet. A creature so bizarre that scientists spent 150 years arguing about what it even was.
“By bringing together material from several collections and using cutting-edge imaging techniques, we have been able to build a clearer picture of the animal than was previously possible, which is really exciting,” Garwood said.
Praearcturus gigas — great and ancient ruler — has waited 415 million years for its proper name. It has finally got one.
