Animal Zeniths: Arthropods

This post is an expansion on an older post that I wrote, Animal Zeniths. Animal Zeniths are as how I define them, animals that are the largest ever known of their kind.

Almost all of these animals have gone extinct, and most of them are the predecessors of animals we know existing today. Some went extinct long before we ever came to be, and yet others of them largely because that we did come to be.

The Arthropods


 Arthropleura, which in Greek means Jointed Ribs, is an extinct genus, that contains what is by far the largest ever known myriapods, as well as largest terrestrial arthropods, and largest land invertebrates, ever to have existed.

Closely related to modern day millipedes and centipedes, Arthropleura had grown to a known maximum size of 2.6 metric meters, or 8.5 feet in total length. Arthropleura is believed as able to have attained this astonishing size in large part due to the uniquely rich, highly oxygenated atmosphere on Earth during the time of its reign, and as well due to its lack of any predators, which, may well have come to be as a result in turn due to the former reason mentioned.

Although often misconceived as ferocious predators, Arthropleura was probably actually herbivorous, meaning of course that it had fed on plant matter, as modern millipedes do today. One reason on which experts base this claim is that Arthropleura did not have any sclerotized mouth parts, as do modern centipedes, all of which are well-known as strictly carnivorous, because had Arthropleura have any such mouth parts, they’d have preserved in at least some of the fossil remains, but as of date, no such remains have ever been found.

If you’ve never see a centipede eat before, make sure that you do sometime. At least, if you have a strong stomach that is. The stronger your stomach is, the bigger the feasting centipede you might want to choose watching. It’s incredible to witness. But can as well be grotesque. In my gut’s opinion, pound-for-pound, centipedes are the most devastating predators on the planet. I really do mean that. They’re absolutely ferocious hunters and eaters.

Somebody’s nightmare probably…
A model reconstruction in a museum, of Arthropleura armata.

Pulmonoscorpius kirktonensis,


Brontoscorpio anglicus

P. kirktonensis, and B. anglicus, are both at claim for the title of largest ever arachnid. Both of them are scorpions, both have gone extinct, and both grew to about the same size, which was roughly 3.3-feet in length. The key difference between these is that P. kirktonensis had lived on land, and B. anglicus lived in water. However, although B. anglicus was indeed aquatic, it was every bit as well indeed a true scorpion with a proper stinger, and should not be confused with Eurypterids, which maybe be known as “sea scorpions” but are not true scorpions.

Some rough scale.

Spiders are as well though arachnids of course…

No spider discovered has been as large as the scorpions above mentioned, but a few spiders have been really quite big, even if not as big. So here’s the zeniths of spiders because they deserve at least to be mentioned.

Megarachne servinei

From since its discovery in 1980, and until its official debunking in 2005, the extinct Megarachne servinei was mistaken by many experts as a spider, and was purported to have a twenty-inch legspan, which had made it at least as it seemed the largest spider of all time. In 2005, all had come to an end for Megarachne servinei’s title reign however, as it was then that it was confirmed in fact as not a spider but a “sea scorpion.” Not even a terrestrial creature.

An incorrect and outdated model reconstruction of Megarachne servinei.

Mongolarachne jurassica

In terms of the proven fossil record, the largest known spider there is nothing to write large about. Mongolarachne jurassica, formerly known as Nephila jurassica, is the largest fossil spider ever found. But with its body measuring at only .97-inches, and front legs spanning only 2.2 inches, Mongolarachne jurassica was only about as large as modern females of the genus Nephila, which contains Golden silk orb-weavers, to offer some perspective. Not so big at all.

The fossil of Mongolarachne jurassica.

The largest extant spider though, can reasonably be split between two of them, the Goliath birdeater, and the Giant huntsman spider. Perhaps the most sensible way in defining this split is through recognition that the Goliath birdeater is the largest by mass, and the Giant Huntsman spider is the largest by legspan.

Goliath birdeater

The Goliath birdeater (Theraphosa blondi) belongs to the Tarantula family, and despite its name, although Goliath birdeaters may be large enough to consume say maybe a humming bird, birds rarely if ever make on the menu for these spiders. But with a legspan of eleven full inches, and weighing over six ounces, T. blondi is a quite formidable spider, and both frogs and mice do make frequent prey items.

Somebody’s pet T. blondi.

The Giant huntsman spider or, Heteropoda maxima, from maximus, which means “the largest,” is the word’s largest spider by legspan. Discovered only in 2001, not too much is yet known about H. maxima, though it’s safe to say that it’s a cave dwelling spider; and being known as it is as the largest spider by legspan, its total length amasses twelve-inches, besting T. blondi in that regard by one full significant inch.

Giant huntsman spider.

Jaekelopterus rhenaniae

Jaekelopterus rhenaniae, of the extinct order Eurypterida, which is the “sea scorpions” I keep speaking of, had rivaled in size with Arthropleura very closely, and attained a length of up to 8.2 feet. Although  known as “sea scorpion,” J. rhenaniae likely lived in freshwater rivers and lakes, not in oceans.

Model reconstruction.

Isotelus rex

Trilobites, which happens to be my personal favorite of the extinct marine arthropods (because as kid I had more than a few fossils of them) were not so terribly large. Some of these creatures did though reach sizes of a bit more than two feet in total length. Isotelus rex for example (Rex–funny name for a trilobite), of which one such fossilized specimen is the largest complete trilobite ever found, measures at twenty-eight inches in length. It’s possible though that some trilobites had grown even larger. Some fossilized fragments of trilobites found have reasoned for lengths as great as 35-inches to be considered at least possible.

The fossil of Isotelus rex.


Even smaller than trilobites, much, much smaller was Saurophthirus, an extinct genus of flea, which had perhaps sustained itself on sucking the blood of pterosaurs. Saurophthirus grew to just one inch in length, but’s pretty impressive for being a flea.

Saurophthirus CGI rendering on Walking with Dinosaurs

 Meganeura monyi

Meganeura, an extinct genus of insect that resembles much in appearance with modern-day dragonflies, and is closely related to them as well, had lived and died during carboniferous period three-hundred-million years ago.

As are modern day dragonflies, Meganeura were predators, but unlike modern-day dragonflies, which relative to us are quite very small, Meganeura was quite large. The largest known species of Meganeura, M. monyi, had a wingspan that measures an estimated twenty-six inches.

Artistic rendering of Meganeura monyi.

Meganeuropsis permiana

Meganeuropsis permiana, another enormous dragonfly-like species of the order Meganisoptera, was perhaps even larger than M. monyi. With the wingspan of one fossilized specimen measuring twenty-eight inches, Meganeuropsis permiana was perhaps the largest insect to ever live.

insect-size-chart1 SMALL
Some scale.


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