11 November 2020: Venomous statistics

Some Australians take perverse pride in the legion of venomous animals infesting the continent and its surrounding seas, from the very small members of the Irukandji group of box jellyfish[i] up to the very large mulga snake[ii].

On the face of it, Australia seems to have had the bum run when it comes to its snakes, spiders, ants, octopuses, cone shells and jellyfish, and this hardly exhausts the list of venomous creatures that call Australia home. On the face of it, if venomous wildlife is your thing then you should be calling Australia home, too.

(As an unpleasant aside, Australia’s venomous biota is not even restricted to its animals; I dare you to read this with the lights off: Australia’s venomous trees.)

If we exclude the 120 kg drop bear[iii], which is sometimes erroneously claimed to use venomous claws to subdue its prey, then the big three that dominate most conversations after a few beers at the pub are the inland taipan, the box jellyfish (particularly the sea wasp), and the Sydney funnel-web spider.

The inland taipan[iv]

For a timid and rarely seen snake, in recent years the inland taipan has garnered a fearsome reputation for itself. In fact, one of its alternative names is the fierce snake, but this is entirely due to its venom, milligram for milligram the most lethal of any of the world’s reptiles. It is often reported that the venom from a 110 mg bite, if carelessly (or maliciously) injected, could kill 100 adult men. The fact that the average dose delivered by an inland taipan is about 44 mg is rarely mentioned, although since this is still enough to kill at least 40 adult men it could be argued I’m being pedantic. Compare this to the most lethal member of the saw-scaled vipers[v], which can reportedly kill six adult males with the amount of venom it delivers with one bite. (We’ll be returning to the saw-scaled viper a little later.)

The chance of encountering the inland taipan, which inhabits that semiarid corner of hell-on-earth between Queensland and South Australia, is vanishingly small. Indeed, in Australia your chance of dying from thirst or a camel stampede is probably greater than dying from a snake bite from any species. It’s also worth noting that the inland taipan has been described as placid and reluctant to strike; of course, if cornered or mishandled it will not hesitate to bite with remarkable speed and precision, and more fool you.

The sea wasp[vi]

The sea wasp is another matter altogether, not because it is remotely vicious, but because it just doesn’t give a damn. All envenomations are accidental. The largest of the box jellyfish, it spends its life floating in the warm tropical waters off northern Australia, Papua New Guinea and Southeast Asia. Well, floating isn’t entirely correct. The sea wasp does swim, but not in the determined way that would get it a place in Australia’s Olympic swimming team; apparently at full pelt they can cover about six metres in a minute. In the right season and the right place, the chance of accidentally bumping into one of these almost transparent jellyfish is depressingly high. Beaches all along the northern, tropical shorelines of Australia have signs warning swimmers of the danger.

Sea wasp.
Photo Creative Commons

An adult sea wasp is made up of a roughly square-shaped bell about 30 centimetres in diameter; 15 tentacles trail from each of the bell’s corners, each of which can be up to three metres long and are covered in around 5,000 cells called cnidoblasts, each of which in turn houses a nematocyst, which is Latin for ‘this will hurt’.[vii]

Nematocysts are the business end of a sea wasp’s venom delivery mechanism. When its prey, usually prawns or small fish, brush against the tentacles, the cnidoblasts release the nematocysts. The nematocysts penetrate the skin of the victim like miniature harpoons and then release their venom. Despite having actual eyes, the sea wasp seems incapable of restraining the cnidoblasts from releasing their load if the tentacles accidentally brush against something which isn’t prey, such as a human. Since this means the sea wasp is missing out on a meal and must now spend what I assume is a lot of energy to rearm the cnidoblasts, this is a serious design fault. Admittedly, that’s small comfort for anyone writhing in the water in unbearable pain, but one can only imagine the cuss words going through what passes for a sea wasp brain.[viii]

According to one study[ix], a sea wasp carries enough venom to kill 60 adults, which considering its size compared to, say, the inland taipan, is some achievement. Nonetheless, most encounters with a sea wasp don’t end with a fatality. The quick application of vinegar to neutralise any nematocysts still attached to the skin, and ice to relieve the pain, is often all that’s necessary. Having said that, one study[x] shows that 8% of envenomations require hospitalisation:

‘Because of the rapidity of fatal C. fleckeri envenoming, the critical window of opportunity for potentially life-saving use of antivenom is much smaller than that for snake envenoming, possibly only minutes. Furthermore, from animal study data, it was calculated that around 12 ampoules of antivenom may be required to counter the effects of a theoretical envenoming containing twice the human lethal dose of venom.’

The lesson here is if you come across a sign at a beach that says beware of box jellyfish (or for that matter crocodiles) consider something marginally safer and decidedly less painful for your daily outing, like jumping off a cliff.

The Sydney funnel-web spider[xi]

I’m an arachnophobe, and this spider pretty well defines the content of my worst nightmares.

I readily admit I’m scared of vampires, malevolent ghosts, land sharks, Brussel sprouts and omelettes – for that matter, any food made mainly from eggs – but my fear of spiders is on a whole other level. Even if I catch a glimpse from the corner of my eye of the completely innocuous daddy longlegs a long shiver will pass down my spine. I don’t know what it is about arachnids that gets me all goosebumpy or triggers my fight or flight instinct (to be honest, my fly or fly-twice-as-fast instinct), but it might have something to do with spiders like huntsmen, wolf spiders, tarantulas and funnel-webs being so damn hairy. It just isn’t right; it’s as if they’d killed a dog or cat, skinned it and donned the fur. Then there’s the eight legs. Six legs on creatures such as ants and earwigs are hard enough to put up with, but eight seems a serious case of overengineering.

Sydney funnel-web.
Photo Creative Commons

Anyway, of all the world’s spiders, the Sydney funnel-web ticks every yuck box: wears dog fur, tick; eight legs, tick; lives in a hole in the ground, tick; likes entering human households, tick; has more than two eyes, tick; has fangs long enough to pierce your toe nail to get to the vulnerable flesh underneath, tick; can kill you with single bite, tick.

Indeed, I cowrote a short story about the Sydney funnel-web with good friend, colleague and fellow-arachnophobe Sean Williams. The story, ‘Atrax’, must have hit a nerve with quite a few people: it won the Aurealis Award for best horror short story in 1999.

The Sydney funnel-web’s lethality can be put down to an extraordinary compound in its venom called δ-atracotoxin (sometimes referred to as delta-hexatoxin[xii]), which bizarrely is brilliant at killing its normal prey of insects, but in small doses causes no harm to mammals … with the single exception of primates. And humans, regrettably in this single instance, are primates. Why the venom should be so damn selective is anyone’s guess, and there have been a few.[xiii]

The other peculiar fact about the Sydney funnel-web is that the male’s venom is up to six times more toxic than the female’s[xiv]. The best theory to explain this is that the male goes wandering during the mating season looking for females and has to defend itself against hungry predators, as hard as it is to imagine any predator being so hard up it needs to feed on such an ugly, hairy and extraordinarily venomous assassin. Admittedly, this doesn’t quite explain why the venom is so effective against primates; I assume almost every human on the continent, like myself, would go to great lengths to avoid antagonising any spider let alone one that can kill you, and as far as I know, humans are the only primates to have made their home in Australia.

Ultimately, the venom’s ability to kill humans is just an accidental byproduct of its evolutionary development.

But, and this is a big ‘but’, no human has died from the bite of a Sydney funnel-web spider since an antivenom became available in 1981.

Most venomous versus most dangerous

And this is where we return to the saw-scaled viper. One of these smallish snakes, the largest will grow no bigger than 90 cm, may only be able knock off six fully grown adults, as opposed to the inland taipan’s potential 100 victims, but nonetheless, to my mind the viper is the more dangerous of the two snakes.

Before I set out my reasons for this, we should remember the saw-scaled viper and the inland taipan only have to kill you once to ruin your day, not six or a hundred times, which would seem – and please excuse the pun – something of an overkill. As far as the average human is concerned, a bite from either of these snakes will see your life flashing before your eyes.

And why do I think the saw-scaled viper is the more dangerous of the two?

First, your chance of encountering a saw-scaled viper on its home turf – anywhere dry in Africa, the Middle East and southern Asia – is dramatically higher than your chance of encountering the inland taipan on its home turf.

Saw-scaled viper.
Photo Creative Commons

Second, the saw-scaled viper is a much testier beast than the inland taipan, and seems inclined to bite anyone passing within striking distance, something the inland taipan is not inclined to do.

Third, your chance of getting good medical care through much of the saw-scaled viper’s range, let alone the appropriate antivenom, can be very small.

Indeed, the saw-scaled viper may be responsible for more human deaths than any other snake, whether we’re talking about other vipers, adders, taipans, cobras, rattlesnakes, kraits or mambas. It’s reported to be responsible for up to 90% of all snakebites in Africa.[xv]

But rather than picking on any one snake, it’s important to understand that snakebites are a serious health problem in most developing countries. According to the World Health Organization[xvi]:

‘Worldwide, up to five million people are bitten by snakes every year. Of these, poisonous (envenoming) snakes cause considerable morbidity and mortality. There are an estimated 2.4 million envenomations (poisonings from snake bites) and 94 000–125 000 deaths annually, with an additional 400 000 amputations and other severe health consequences, such as infection, tetanus, scarring, contractures, and psychological sequelae. Poor access to health care and scarcity of antivenom increases the severity of the injuries and their outcomes.’

It seems to me these statistics, which barely reflect the pain, misery and social desolation that can be caused by a snakebite, are the ones we should obsess over, rather than how many humans can be killed by a single and remarkably shy Australian snake.

One final point. On average, more Australians die each year from the stings and bites of ants, wasps, bees and ticks than snakebite, largely thanks to anaphylactic shock (and not prophylactic shock as I once tipsily declaimed). From 2000 to 2013, 27 Australians died from snakebite; over the same period, 32 Australians died from animals that fly and crawl around us every day of our lives without us giving them a second thought. In the same period, no one died from a spider, scorpion or centipede bite, and only three people died as a result of envenomation from a marine creature[xvii].

To put these statistics into proper perspective, horses were responsible for the deaths of 77 Australians between 2000 and 2010[xviii]. To make the perspective even sharper, consider that between 2000 and 2013, more than 21,000 Australians died in car accidents[xix].

By the way, in those same thirteen years, two people were recorded to have died from an unknown animal or plant. I’m betting it was a drop-bear.


[i] Genus Carukiidae.

[ii] Pseudechis australis.

[iii] Thylarctos plummetus – in my humble opinion, the best species name ever.

[iv] Oxyuranus microlepidotus.

[v] Echis carinatus.

[vi] Chironex fleckeri.

[vii] Disappointingly, and rather mundanely, nematocyst is Latin for ‘a cell with threads’.

[viii] In fact, sea wasps don’t have a brain as such, or anything else we might recognise as a central nervous system. But it does have something: ‘The box jellyfish’s nervous system is more developed than that of many other jellyfish. They possess a nerve ring around the base of the bell that coordinates their pulsing movements … ’ See https://en.wikipedia.org/wiki/Box_jellyfish.

[ix] http://emedicine.medscape.com/article/769538-overview

[x] https://www.mja.com.au/journal/2005/183/11/prospective-study-chironex-fleckeri-and-other-box-jellyfish-stings-top-end#authors

[xi] Atrax robustus

[xii] For example, see:

https://theconversation.com/i-didnt-mean-to-hurt-you-new-research-shows-funnel-webs-dont-set-out-to-kill-humans-146406

[xiii] For an explanation that makes sense to me, see: https://biology.stackexchange.com/questions/8825/why-is-funnel-web-spider-venom-so-lethal-to-humans-and-not-so-much-for-other-mam

[xiv] https://en.wikipedia.org/wiki/Delta_atracotoxin

[xv] James Cook University toxinologist Professor Jamie Seymour carefully lays out what makes one venomous animal more dangerous than another in the National Geographic documentary World’s Worst Venom, not only comparing and ranking the inland taipan with other snakes, but also including sea stingers, spiders, scorpions and many other venomous creatures. Well worth a look if you can get your hands on it. See:

https://www.imdb.com/title/tt1132196/?ref_=rvi_tt

[xvi] https://www.who.int/en/news-room/fact-sheets/detail/animal-bites

[xvii] https://biomedicalsciences.unimelb.edu.au/news-and-events/archive-news/professor-daniel-hoyer-and-dr-ronelle-welton-featured-academics-in-pursuit-article

[xviii] https://www.australiangeographic.com.au/topics/wildlife/2016/03/here-are-the-animals-really-most-likely-to-kill-you-in-australia/

[xix] https://en.wikipedia.org/wiki/List_of_motor_vehicle_deaths_in_Australia_by_year

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