There is something primally horrifying about a spider or insect attacking and eating a furry or feathered animal. But this unsettling event happens all the time

You have probably seen the viral video of an Australian huntsman spider dragging a mouse up the side of a fridge. Well, we can top that.

The huntsman footage is undoubtedly remarkable. The spider is displaying amazing strength and extraordinary gripping power: the surface of that fridge is really smooth, hardly conducive to easy climbing.

But in one key respect, it is trivial: the spider probably did not kill the mouse. The mouse's stiff tail and saggy belly are both clues that it had been dead for a while. So what the video showed was, in fact, nothing more than a rather impressive feat of heavy-duty scavenging.

However, look deeper into the animal kingdom and there are plenty of examples of "creepy-crawlies" like spiders subduing and killing animals far larger than themselves.

For instance, in a paper published in December 2016 researchers described a dramatic incident in Brazil. A tarantula (Grammostola quirogai) was found eating a snake that it had apparently subdued and killed. The snake, an Almaden ground snake, was 15in (39cm) long.

This shudder-inducing behaviour is a lot more common than you might think.

Spiders and insects are fundamentally different to us because they do not have backbones: they are "invertebrates". We, along with dogs, eagles, frogs and fish, are vertebrates – animals with backbones.

Dragonfly larvae are major aquatic predators that often eat tadpoles

Vertebrates can grow far larger than invertebrates. Outside of B movies, there are no insects that can remotely rival an elephant for size. So we tend to think of vertebrates eating invertebrates – birds catching flies, chimpanzees eating termites, and anteaters doing the obvious – but not the other way around.

The idea of an invertebrate eating a vertebrate often triggers a shiver of horror, even if you do not know the technical words to describe it. Think of the giant spider Shelob in The Return of the King, Aragog in Harry Potter, or even just the name "Goliath bird-eating spider". It all feels rather spooky, and somehow against the natural order of things.

But nature neither knows nor cares about our preconceptions. There are plenty of large, fast and (often) highly venomous predators that lack backbones. It does not matter to them if their prey is a vertebrate: maybe the spine gives a bit of extra crunch to the munch, but nothing more.

One recent report comes from the German herpetology journal Salamandra. In April 2016, biologists from Brazil recorded the first ever examples of dragonfly larvae eating adult frogs.

Dragonfly larvae are major aquatic predators that often eat tadpoles, and this has forced the tadpoles to come up with devious defense strategies. The tadpoles of leopard frogs will speed up their maturation if they are in a pond with dragonfly larvae. Other species of tadpoles hide, or develop ornamentations on their tails to trick the dragonfly larvae into striking at less vulnerable parts of their bodies.

Scolopendra centipedes are particularly ferocious. They can be over 30cm long

Dragonfly larvae might be the tigers of the water-weed jungle, but they were not thought to attack adult frogs. The new study indicates that they do, at least occasionally. The voracious larvae climbed out of their ponds onto water plants, then leapt onto the frogs and began eating them alive, while the frogs tried unsuccessfully to escape.

But dragonfly involvement in using vertebrates as victuals does not end there. Now and again, adult dragonflies also get in on the act. For instance, there is a remarkable photo of a large Canadian dragonfly called a dragonhunter that caught a ruby-throated hummingbird in mid-air and began to feed on it. However, this is clearly not a common occurrence: the only other known case happened in 1977.

Elsewhere, other invertebrates are regular hunters of vertebrates. Some of the most dedicated are the Scolopendra centipedes.

Most centipedes are predators, but Scolopendra centipedes are particularly ferocious. They can be over 30cm long, and have a set of powerful fangs: these are technically called ''forcipules'', because instead of true fangs they are actually modified front legs.

These centipedes are not native to the UK, though they do occasionally hitch a ride in on imported fruit. There are five European species, but they rarely exceed 16cm and feed on other invertebrates. But things change in the tropics, where some cave-dwelling Scolopendra species are major predators of roosting bats.

Scolopendrid venom contains between 10 and 62 proteins that can, among other things, stop an animal's heart

The centipede scuttles up onto the ceiling of the bats' cave and anchors itself with its rear half-dozen pairs of legs. These are notably thickened and muscular, with extra-large and sharp claws at the tips, to keep a firm grip. Once in position, the Scolopendra either swings the rest of its body down into the bats' fly-space and grabs one as it flits past, or pulls one off the wall as it dozes.

Apart from bats, these well-armoured beasts have been known to take rats, lizards, frogs and even snakes. We are not talking about innocuous grass snakes, either: these centipedes have been recorded overpowering species as fast and toxic as Indian coral snakes.

Of course it is worth remembering that centipedes are some of the oldest surviving venom-bearing animals. Ones much like those around today, forcipules and all, have been found in rocks 420 million years old. Mammals, on the other paw, only appeared some 208 million years ago. This means that, when the first shrew-sized mammals poked their whiskery noses into the world, there were large venom-charged centipedes waiting for them.  

Apart from their sheer size, the thing that makes scolopendrids such Hollywood-worthy predators is their venom.

Made inside the forcipules, scolopendrid venom contains between 10 and 62 proteins that can, among other things, stop an animal's heart or mess with its metabolism. Some species have venom potent enough to kill children, large dogs and, in the case of the unfortunate individual who accidentally swallowed a small one, army officers.

It also seems that scolopendrids do not know when to quit.

In a study published in 2014, Dragan Arsovski and colleagues reported that they had found a female horn-nosed viper dead, with its stomach burst open. The 20cm-long animal had rather rashly decided to swallow a live 15cm Scolopendra. This turned out to be a mistake: the centipede seems to have eaten all the snake's internal organs, then tried to chew its way to freedom through the snake's body wall. As you can see from the picture, it very nearly made it.

The scolopendrids do not always get their own way, though. On the Caribbean island of Hispaniola there is a lizard called Warren's giant galliwasp, which seems to specialise in hunting Scolopendra centipedes. It is, however, exceedingly rare – albeit for reasons unrelated to its diet.

Watery habitats are also rife with invertebrate predators.

Look at any body of water in summer and you will see long-legged insects, skittering between pond weeds, dimple-balanced on the water surface. They feed by sucking the innards out of drowning insects. But below the water surface, concealed in weeds and dead leaves, lurk waterscorpions: 2-cm-long ambush predators that eat whatever comes into reach.

In the tropics these insects are scaled up, becoming the giant water bugs. The largest species reach 12cm.

They conceal themselves in vegetation and then pounce. They have a stout, tube-like proboscis with which they can impale their prey, inject digestive juices, and then suck up the resulting "soup". Large, hook-like front legs make sure there is little chance of escape.

Giant water bugs eat a lot of fish and tadpoles, as well as adult frogs and water snakes. There is even a report of a baby terrapin falling prey.

Giant water bugs and scolopendrid centipedes are ambush predators. So while we might find their attacks creepy, at least the prey animal is dead before it is ingested.

However, crabs are not so considerate. If an animal is in the wrong place at the wrong time and cannot fight back, it faces death by a thousand claws, or mini-jaw cuts.

One such example comes from Taiwan. A study published in 2005 reported that breeding pairs of Kuhl's fanged frogs were being preyed on by Rathbun's creek crabs. Conceivably the frogs were too distracted to notice the crabs' approach.

Pterostichus niger is even less sporting. It preys on newts while they are hibernating underground

A similar case was described in 2013 from Broughton Island, north of Sydney in Australia. Graham Pyke of the University of Technology Sydney found that golden bell frogs, already endangered from habitat loss, have to cope with an annual influx of swift-footed shore crabs.

The crabs migrate up from the inter-tidal zone where they normally feed, to feast on the annual gathering of breeding adult bell frogs and, a little later, their tadpoles.

You might think that tadpoles living far away from ponds would be safe, but they are not. Panamanian green and black poison dart frogs lay their eggs in water-filled tree holes, but there are reports of these tree-top havens being found and plundered by freshwater crabs. The crabs also ascend the thin branches of water-side shrubs to feed on the eggs covering their leaves, which are placed there by female glass frogs in the hope that they might develop safely.

Similarly, on Israel's central coastal plain, Epomis beetles go looking for young frogs and salamanders. When they find one, they jump on its back and bite it at the base of the spine. Once the animal stops moving, they start to feed. Studies by Gil Wizen and Avital Gastith of Tel-Aviv University have shown that amphibians are pretty much all these dark blue and orange beetles eat.   

A Polish cave beetle called Pterostichus niger is even less sporting. It preys on newts while they are hibernating underground. While the newts are too dozy too move, the beetle, which has a special cold-start metabolism, tracks them down and feeds at leisure.

Perhaps worse still, for the sheer creeping inevitability, is death by leeches. There are records from as places as diverse as Brazil, India and the southern USA of leeches attaching themselves to adult frogs and toadskilling the luckless victims – as well as ingesting whole clutches of frog spawn and even killing water-going garter snakes. 

And then, of course, there are the spiders.

Many people fear spiders to some degree, even when all they are doing is feeding on insects like flies. The "ew" factor soars if these eight-legged hairies feed on our nearer relatives.

Most bats eaten by spiders are first caught in webs

A 2012 review found reports of 54 bird species from 23 families being trapped in spider webs in the USA alone.

Most of the webs were made by large orb-web spinners of the genus Nephila. Adult females have bodies the size of a human thumb and their webs can exceed 3m in width. The majority of the victims were hummingbirds, weighing less than 15g. When found, many were already wrapped in silk and, having been envenomated, were ready to be liquefied and sucked dry

Similarly, a 2007 study reported that a common tody-flycatcher had been found wrapped and ready in an orb-web in Brazil. The Nephilengys cruentata spider was almost as big as the 7g bird.

That weight is about the same as that of a large proboscis bat, so it should be no surprise that they too have been found in spider webs. In the case of one observed in 2005 by Kansas University tropical biologist Robert Timm, the animal was wrapped in silk and an Argiope savignyi spider was feeding on it.

Most bats eaten by spiders are first caught in webs, but not all. In India, the splendidly-named reddish parachute tarantula has been seen feeding on Kelaart's pipistrelle. At 8cm long, the animals are about the same size.

Spiders can also take amphibians. For instance, a 2010 paper described a wolf spider preying on a newly-metamorphosed toad.

Meanwhile, two exotic invertebrates were accidentally introduced to Christmas Island and may have been responsible for the extinction of the native bat, the Christmas Island pipistrelle. Giant Scolopendra centipedes did what they do best, and yellow crazy ants may have eaten the last four bats alive in their roost.

Finally, we have to mention the Goliath bird-eating spider, which is a contender for the world's largest spider. Despite its name it rarely attacks birds, but "rarely" does not mean "never". In October 2016, researchers reported that a Goliath bird-eating spider had killed a scale-backed antbird, after the bird became entangled in some netting.

These huge spiders bring us back to the importance of size. While the biggest vertebrates dwarf all invertebrates, there are plenty of invertebrates that are big enough to take on small vertebrates.

We might not use the word "vertebrate", but a dog is clearly more similar to us than a giant centipede

Being large animals, we are not used to this, but something tiny like a hummingbird would have a different perspective. Adults get snatched by praying mantises and dragonflies, and bullied away from feeders by sugar-hungry hornets. There are even records of nestling hummingbirds, which are absolutely minuscule, being picked up by wasps and taken back to the nest to feed their brood.

Most of us are happy to watch vertebrates hunting vertebrates; if lions kill a giraffe, we might feel sadness but not revulsion, and we cheer when the baby iguana escapes the racer snakes. Similarly, if a vertebrate hunts an invertebrate, that seems normal: an early bird catching the worm is simply being enterprising.

But invertebrates eating vertebrates is another matter. We find ourselves horrified by crabs preying on baby turtles, wasps targeting nestling birds, or a giant centipede munching on a bat. Somehow it seems wrong, as if the natural order has been turned on its head – but why?

Perhaps it is that we instinctively recognise an evolutionary truth: other vertebrates are more like us than invertebrates. We might not use the word "vertebrate", but a dog is clearly more similar to us than a giant centipede. Not only does the dog have hair and the same number of limbs, it also behaves in understandable ways, displaying familiar emotions like happiness and anger.

The complex venoms of the giant centipedes are now under intense scrutiny for the medical benefits the proteins in their venoms might bring

In human prehistory, being able to predict an animal's behaviour made it, in some way, safe. But we cannot understand invertebrates in the same way that we understand dogs, lions or eagles. They are just too alien, their behaviour too strange and their bodies too dissimilar. They do not have waggy tails and their eyes are never big and soulful.

Perhaps on some fundamental level we do not trust invertebrates, so we are thankful that their strangeness does not manifest as predation. That would explain why we are so disturbed when it does. If a bat eats a spider, we nod knowingly from the sofa; but if a spider eats a bat, we freak out behind the cushions.

But it would be a mistake to write off these apparently alarming invertebrates as just a source of nightmares and bad horror movies. Even these seemingly freaky creatures are proving to be valuable.

In particular, the complex venoms of the giant centipedes are now under intense scrutiny for the medical benefits the proteins in their venoms might bring. So far, compounds with exciting potential for breast cancer, heart blood flow, asthma, and thrombosis are under study. The animals have even gained a new name: "medicinal centipedes".

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