More than a hundred million years before fish crawled out of water and evolved into walking, four-legged vertebrates, invertebrates ruled over Earth’s terrestrial environments unchallenged.
These pioneering invertebrates made their first appearance on land some 470 million years ago. Around the same time, plants also emerged and began to seed life across the previously barren continents.
This ‘land of bugs’ was home to some of the most bizarre creatures that ever lived. They include millipedes larger than a king-size duvet to giant dragonflies with wingspans as wide as a common kestrel's.
A lot of these supersized invertebrates lived during the Carboniferous (359 to 299 million years ago). It was a time when a surplus of oxygen in the Earth’s atmosphere allowed them to grow to record-breaking sizes.
Meganeuropsis
Long before pterosaurs and birds evolved powered flight and took over the skies, insects dominated this ecological space.
The largest amongst them was Meganeuropsis, a dragonfly-like insect that’s part of a now-extinct group known as griffenflies, or meganisopterans.
Meganeuropsis had a 71cm-wide wingspan, which is roughly the same as a common kestrel’s. It lived in what is now the US during the Permian (290-283 million years ago). It buzzed around ponds and slow-moving rivers as it hunted other flying insects and even some small, lizard-like vertebrates.
It’s thought Meganeuropsis used its spiny front limbs as a trap to ensnare its prey.
A close relative of Meganeuropsis, Meganeura, had a similarly wide wingspan (around 70cm). It lived a few million years earlier during the Carboniferous (305-299 million years ago).
A surplus of oxygen in the atmosphere isn’t the only factor that set these insects on the evolutionary path towards gigantism. Some researchers think they grew so large in response to their prey, plant-eating palaeodictyopterans, also increasing in size.
Arthropleura
At 2.5m in length, Arthropleura is widely considered the largest invertebrate to ever walk the Earth. This giant ancestor of today’s millipedes is not an insect but a myriapod – an adjacent yet distinct group of invertebrates (or rather arthropods) that includes millipedes and centipedes.
Arthropleura lived across Europe and North America for more than 50 million years between the Early Carboniferous and the Early Permian. Like many bugs, living and extinct, it was a detritivore that fed on pretty much any rotting biological material it came across, from dead trees to dead animals.
Some fossil trackways, discovered in Nova Scotia, Canada, suggest that Arthropleura had short and closely-packed legs, which would have made it very slow.
For a long time, it was thought Arthropleura died out at the end of the Carboniferous and during an event known as the Carboniferous Rainforest Collapse. However, recent fossil finds suggest it survived into the Permian.
It may have ultimately faced extinction as a result of competition with some early reptiles, such as pelycosaurs.
Pulmonoscorpius
The largest scorpion alive today, the aptly named giant forest scorpion, measures 23cm in length and is, quite rightly, considered one of the world’s scariest bugs.
Now imagine a scorpion that was more than twice as long (around 70cm) and roughly the same size as a housecat – terrifying, right?
Pulmonoscorpius is the largest, fully terrestrial scorpion currently known to science. It had all the terrifying features of today’s scorpions – two grasping claws, eight spindly legs, and a powerful, stinging tail – but it also had large lateral eyes, a feature not shared by today’s scorpions.
It also lacked adaptations for a burrowing lifestyle, suggesting it was a diurnal predator that spent most of its time scuttling overground.
What Pulmonoscorpius ate is unclear, but it’s likely that it hunted other arthropods and maybe even some small tetrapods, such as primitive amphibians.
It lived in what is now Scotland during the Early Carboniferous (336-326 million years ago), back when this area lay at the equator and was covered by vast, tropical swamps.
Interestingly, fossils of this giant scorpion have only ever been found at one site – East Kirkton Quarry, which lies just 20 miles west of Edinburgh.
Mazothairos
This flying insect wasn’t quite as large as Meganeuropsis, but with a wingspan that measured 56cm across they were still giants of their time.
Mazothairos belongs to a diverse group of insects known as palaeodictyopterans, some of which would have been prey for the likes of Meganeuropsis and Meganeura.
What makes Mazothairos and other palaeodictyopterans unique amongst insects are their sharp, piercing mouthparts, which they may have used to suck the liquids out of plant tissues, and their six wings.
Most other insects have four wings, or two pairs, but palaeodictyopterans had an extra pair just below their heads. These were more ‘winglets’ than ‘wings’ and weren’t actually used for flight, but they have told researchers a lot about how wings may have evolved in insects.
Mazothairos lived during the Carboniferous (around 309 million years ago) in what is now Illinois, US. This area was part of a large river delta system during the Carboniferous and was home to a diverse array of plants and animals.
A lot of these, including Mazothairos, are preserved as fossils in the world-famous Mazon Creek fossil beds. This area is renowned for its exceptionally preserved, painting-like fossils, known as lagerstätten.
Chimerarachne
While it may have eight legs, fangs, twin feelers, and silk-producing spinnerets on its back-end, Chimerarachne is no spider. Instead, this spider-like bug belongs to a long-lost group of ‘almost spiders’ that lived alongside true spiders for nearly 200 million years.
It’s also a lot smaller than most modern spiders, measuring just 2.5mm across.
Chimerarachne’s defining feature, and also what sets it apart from true spiders, is its 3mm-long, whip-like tail – a feature it shares with its ancient ancestors, known as uraraneids.
This tail is covered in short, hair-like structures, which have led researchers to interpret it as some kind of sensory organ that it may have swished from side to side as it sought out prey.
Chimerarachne was first described in 2018 from several specimens that were found encased in amber.
This kind of preservation is usually quite rare, but in Myanmar – where Chimerarachne was discovered and where amber forests were widespread during the Late Cretaceous (around 100 million years ago) – this sticky tree resin has preserved more than 2,500 species of arthropods, as well as some plants and even several small vertebrates.
Ceratomyrmex
It’s no surprise that an insect with the nickname ‘Hell Ant’ has made this particular list. This 0.5cm-long, prehistoric ant looked a lot like today’s ants, though it sported two distinct features – scythe-like mandibles and a huge horn.
Ceratomyrmex isn’t the only ‘Hell Ant’; during the Late Cretaceous (100-79 million years ago), there were as many as 17 different species that belonged to this diverse group, and they lived all over the world.
Like its relatives, Ceratomyrmex was a deadly hunter and one that used its mandibles and horn to subdue its prey. We know this thanks to an incredible find of Myanmarese amber that captures a Ceratomyrmex in the act of attacking and pinning down an extinct relative of today’s cockroaches.
Other ‘Hell Ants’ had equally impressive head décor. Linguamyrmex, which like Ceratomyrmex also lived in Asia, had a metal-tipped spear growing out of its head.
It used this reinforced spear to skewer its prey, which it would then carry away to its nest to feed its queen and the rest of its colony.
Manipulator
Another bug known from specimens preserved in Myanmarese amber is a long-extinct relative of today’s cockroaches known as Manipulator.
This early cockroach lived during the Late Cretaceous (around 99 million years ago) and looked superficially like a praying mantis, with a long neck, freely rotating head, and freakishly long legs.
Its long forelimbs were also covered in spines that allowed it to reach out and grab its prey, just like a praying mantis does.
These features have led researchers to suggest that Manipulator was a predator, but new finds in 2022 have shed further light on this particular insect and suggest that it may have been a plant-eater, and one with a particular taste for flowers.
Manipulator, like Chimerarachne and Ceratomyrmex, was found in the Hukawng Valley in northern Myanmar. This area was not only home to thousands of species of bugs, but birds and dinosaurs too.
In 2016 and 2017, a team of researchers found the tail of an undetermined theropod and the remains of a baby bird, also encased in pieces of amber.
Hibbertopterus
Arthropleura may be the largest bug to ever walk the Earth, but Hibbertopterus is the heaviest. This giant bug looks like a woodlouse, but it’s actually part of a group of aquatic arthropods known as eurypterids, or ‘sea scorpions’.
At 2m in length it’s not quite as large as the largest eurypterid, Jaekelopterus (2.5m), but its broad and compact body is widely considered to make it not only the heaviest eurypterid, but also the heaviest arthropod.
Hibbertopterus lived from the Middle Devonian to the Late Carboniferous (388-304 million years ago) and is known from fossils found in Scotland, South Africa, and the US.
Unlike a lot of other eurypterids, Hibbertopterus wasn’t an active predator. Instead, it fed by using its spine-covered forelimbs to rake through muddy substrates in search of small, tasty invertebrates.
While Hibbertopterus lived primarily underwater, some fossilised trackways found in Scotland suggest that it may have been capable of walking on land. It’s unclear exactly how it survived out of water.
Some researchers think it may have been able to breathe for short periods while its gills remained wet, while others suspect it may have had a dual respiratory system.
Titanomyrma
As ants go, Titanomyrma was a giant and perhaps the largest to ever live. While workers maxed out at sizes of ~3cm, queens reached ‘colossal’ sizes of 7cm and sported wings that measured 16cm across, making them comparable in size to today’s hummingbirds.
Titanomyrma is known from a collection of exceptional fossils that have even preserved the delicate wings of queens. From studies of these fossils, researchers have deduced that Titanomyrma, unlike 71% of modern ant species, didn’t have a stinger and instead sprayed formic acid from its digestive tract as a defence mechanism.
It may have also been carnivorous, feeding on other insects and small, already-dead animals.
Titanomyrma lived during the Eocene (around 47 million years ago) and fossils of it and its close relatives have been found in both Germany and North America, leaving researchers puzzled as to how they crossed continents.
It has been suggested that land bridges linking Eurasia to North America and warm temperatures around the Arctic during the Eocene may have enabled this migration of giant ants, though there’s currently no consensus on this particular idea.
Mosquitoes
While most are larger, heavier, and look a whole lot more menacing, none of the bugs on this list are quite as deadly as mosquitoes.
These silent assassins are responsible for killing roughly 52 billion of the 108 billion people estimated to have lived throughout human history – that’s almost half, and more than all wars combined have killed!
What makes mosquitoes so deadly is that they’re vectors, or carriers, of some of the deadliest parasitic diseases (malaria and filariasis) and viral diseases (yellow fever and dengue fever).
As they bite, their pathogen-filled saliva is transferred into the blood of their host, causing an itchy rash and infecting them with whatever disease they are carrying. On average, mosquitoes are estimated to kill 725,000 people per year by transmitting deadly diseases.
As a group, mosquitoes have been around for nearly 125 million years, meaning they once lived alongside dinosaurs. And like those that live today, early mosquitoes were also bloodsuckers.
In the 1980s, a fossil of a 46-million-year-old mosquito, full from its last bloody meal, was found in Montana, US. It’s unclear what animal this blood came from – and before you email in to ask, no, it’s impossible to extract this animal’s DNA and reconstruct it in a lab, à la Jurassic Park.