Largest terrestrial invertebrate ever
Who
Arthropleura armata
What
2.5 metre(s)
Where
United Kingdom ()
When

The largest land-based invertebrate (animal without a backbone) ever was a gigantic millipede called Arthropleura armata, whose total length was up to 2.6 metres (8 feet 6 inches) and with a width exceeding 0.45 metres (1 foot 5 inches). It weighed around 50 kilograms (110 pounds), its multi-segmented body was heavily plated, and possessed between 32 and 64 legs. Arthropleura lived approximately 345 to 295 million years ago, from the Lower Carboniferous Period to the Lower Permian Period, in land areas that are now the UK, Germany and north-east North America. The reason why it was able to grow so large is that, back then, the percentage of oxygen present in the atmosphere was considerably higher than it is today, thereby enhancing the creature's respiratory efficiency.


Originally, Arthropleura was thought to be an active predator, and reconstructions of its likely appearance in life depicted it as a giant centipede-like creature, as centipedes are carnivorous. More recently, however, studies have concluded that it was more likely to have been a millipede, and, like millipedes, to have been herbivorous. Supporting this proposition is that no fossilized jawparts of Arthropleura have ever been found. Yet the jaws of centipedes and other invertebrate predators are highly sclerotized and very powerful, so if those of Arthropleura had been like this, we would expect their remains to have been preserved alongside its fossilized plated body. Consequently, Arthropleura is nowadays placed within the millipedes' taxonomic order, Diplopoda.

The most recent (and largest) Arthropleura specimen was found by chance on a beach beside Howick Bay in Northumberland, UK, in 2018. It may not necessarily be the fossil of a deceased millipede but potentially an exoskeleton cast off by one of these giant insects. A comprehensive study detailing its remains was published in the Journal of the Geological Society on 21 December 2021.