What's the world's deadliest spider?

Black widows are among the deadliest spiders in the United States. See more pictures of arachnids.
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If Hollywood were a reliable source of scientific information, figuring out the most dangerous spi­der in the world would be a no-brainer. The furry tarantula has crawled across cinema screens in countless horror, sci-fi and adventure flicks, causing audiences to grip their chair arms in suspense. Will the hero escape quickly enough to avoid the poisonous bite of the ferocious spider?

In reality, our arachnophobia-induced aversion to tarantulas is misplaced. The formidable spider's bristly hairs are more likely to irritate than its venom. Although a bite from the passive tarantula will induce topical pain, it won't kill you unless you're highly allergic.

Of the nearly 40,000 known spider species, only a tiny fraction of them can inflict any significant pain in humans. In fact, there is no wholly accepted consensus on the world's deadliest spider because, by and large, spiders aren't much of a threat to our well-being. At the same time, the number of spider bites is often incredibly over-reported. In one study of 600 hospital patients claiming to have been bitten by brown recluse spiders in Southern California, doctors could confirm only 20 percent of the bite wounds as coming from the spider [source: Vetter and Visscher].

That said, there are a handful of arachnids around the world that it would be in our best interests to avoid. The overall morbidity rate of venomous spiders remains below 10 percent, but some of their poisons can induce tissue degeneration, cell death, nausea and other unpleasant side effects.

Before we get to the culprits on the list of the world's most dangerous spiders, it may be helpful to know how these arachnids deliver their fearsome bites. As you can read in How Spiders Work, venomous spiders are equipped with a poison gland that harbors the dangerous chemicals. Those glands are connected to a set of fangs that spiders use to deliver the poison into their victims. The fangs usually remain tucked inside the spider's jaws until it feels threatened. When that happens, it releases its fangs, digging them into the victim's body and secreting poison. Not all spider bites are potentially wounding. Many spiders give dry bites without venom as a warning.

Think it couldn't get scarier than running into a brown recluse or black widow on a bad night? Think again.

Two Deadly Spiders

The Sydney Funnel-web spider is often called the world's deadliest spider, with fangs strong enough to penetrate a toenail.
The Sydney Funnel-web spider is often called the world's deadliest spider, with fangs strong enough to penetrate a toenail.
Ian Waldie/Getty Images

In the United States, people worry most about the fangs of the brown recluse and black widow. A bite from a brown recluse can leave you with significant scarring from tissue breakdown, but odds are strongly in favor of your survival. You can identify brown recluses by the violin-shaped marking on their abdomens. Statistically, black widows, with their red hourglass calling card, pose more of a threat to humans. Before doctors discovered antivenin for the widow family of spiders, the mortality rate for bite victims was around 5 percent [source: Vetter and Visscher].

Although there isn't a definitive answer to what the world's deadliest spider is, experts often place the Sydney Funnel-web spider, or Atrax robustus, at the top of the list of poisonous spiders. This arachnid species bears responsibility for the highest number of bites and human fatalities among all spiders [source: Alcock]. With fangs strong enough to penetrate finger and toenails, in extreme cases, a Funnel-web bite can kill a person in 15 minutes.

As you can infer from its name, the Sydney Funnel-web spider is native to Australia, found across a 99-mile (160-kilometer) radius around Sydney [source: Australian Venom Compendium]. Humans encounter dark-colored Funnel-web spiders mostly during mating seasons in summer and fall, when the males leave their burrows in search of females [source: Australia Museum]. However, since the discovery of a Funnel-web antivenin in 1980, no one has died from its bite. Behaviorally, Funnel-web spiders are more dangerous than black widows or brown recluses because they become aggressive when threatened. If you tried to shoo one away, it's less likely to skitter off. The male Funnel-webs are more potentially harmful than females and juvenile spiders -- and they're the most likely to attack.

The active ingredient in Funnel-web venom is delta-atracotoxin. This amino acid chain is a neurotoxin that causes our nerve cells to continually fire once it enters the bloodstream. That rapid firing sparks intense pain at the bite site that will start within 28 minutes of the actual bite [source: Alcock]. In general, spider venom affects humans by interacting with ion receptors in our cells [source: Escoubas, Diochot and Corzo]. When that happens, it unnaturally excites the cells, which can lead to pain and cell dysfunction.

­On the other side of the world, the Brazilian wandering spider, or Phoneutria nigriven, often ranks second, below the Sydney Funnel-web, as the world's deadliest spider. The 2007 Guinness Book of World Records actually named it the most venomous spider in the world because it's capable of injecting 1 to 2 milligrams of venom in its victims [source: Richards]. You can spot these by the red hairs on their necks. Like the Funnel-web, the Brazilian wandering spider has aggressive tendencies and is known as a hunting spider. Like other spider venoms, the Brazilian wandering spider's affects sodium ion receptors, particularly in muscle and sensory cells [source: Meier and White]. Bites from these spiders account for around half of spider-related hospitalizations in South America [source: Meier and White].

Getting bitten by any of these spiders would probably be an unpleasant experience. But today, even the most venomous arachnids with the largest, sharpest fangs don't pose much of a health threat to humans thanks to antivenins. As a rule of thumb, be careful when you're working in a dark corner of your basement or storage shed. Spiders often don't want to attack, but they'll defend their territory when necessary.

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Sources

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