This Australian spider evolved to kill us — here’s why

Fear of spiders is so common it consistently ranks in lists of the most common human phobias.

A study published in October in the journal Proceedings of the National Academy of Sciences gives us yet another reason to be terrified of spiders — or at least, one deadly Sydney funnel-web spider. It seems this particular Australian funnel-web spider has evolved a deadly defense system to target vertebrates.

Specifically: humans.

The Sydney funnel-web spider's venom fascinates us just as much as it kills us. The venom's neurotoxins can cause death within 15 minutes after the spider's fangs pierce human flesh.

The spider kills using toxic chemicals known as Delta-hexatoxins, which attack the nervous system. Symptoms include muscle spasms, vomiting, profuse sweating, and, of course, death.

While the funnel-web isn't the only spider to inject humans with poisonous venom, the evolutionary adaptation to target humans specifically is quite distinct.

The spiders originally deployed this lethal defense mechanism against other insect predators, but funnel-web spiders — male funnel-web spiders, in particular — have seemingly evolved to kill humans with their venom, too, the researchers found.

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For decades, researchers just didn't understand why male funnel-web spiders had evolved to poison humans above all other vertebrates — especially since humans are not their natural predators.

"It has puzzled scientists why these toxins are so deadly to humans, when they and other primates, haven't featured as either prey or predator during the spider's evolution," Bryan Fry, associate professor at the University of Queensland, said in a statement at the time.

"And we couldn't understand why most human deaths were being caused by male funnel-web spiders, which seemingly had much deadlier venom than females."

But after conducting their experiment, the researchers have a better grasp of the method behind the deadly madness.

Through genetic sequencing, the researchers discovered that this is all "an unfortunate evolutionary coincidence."

Humans were never the primary target of the funnel-web spider's venom. The venom evolved to target other vertebrates — birds, lizards, and so on — and just happened to kill humans, too.

Male funnel-web spiders also are more likely to kill with their venom due to evolutionary adaptations, according to the researchers. They are more likely than females to wander long distances in search of mates, encountering predators along the way.

Ultimately, there may be a silver lining to this weird and awful trait: The unique susceptibility of humans to funnel-web spider venom could yield new insights in medical treatment or the development of insecticides, the researchers concluded.

For the time being, however, we are still at the mercy of this remarkably lethal Aussie creature.

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