What's the Most Venomous Spider in the World?

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. 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. That's one dangerous spider! However, since the discovery of a funnel-web antivenin in 1980, no one has died from its bite.

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].

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.

Toxins in Spider Venom

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.

You can spot these arachnids (sometimes called banana spiders) 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.

Statistically, black widow spiders (Latrodectus mactans), with their red hourglass calling card, pose more of a threat than brown recluses to humans. These are the most venomous spiders you are likely to encounter in the United States, with a potent venom that is believed to be 15 times more powerful than that of a common rattlesnake.

Still, the dose makes the poison, and most black widow spider bites won't inject enough venom to kill a person.

A useful statistic bears this out: Before doctors discovered antivenin for the widow family of spiders, the mortality rate for bite victims was around only 5 percent. Now, with the antivenin, the rate is even lower [source: Vetter and Visscher].

That doesn't mean you should go around harassing black widows, but you can view them with a little less fear.

The brown widow spider (Latrodectus geometricus) is somewhat similar in appearance to the black widow, as mature specimens of both have an hourglass-shaped marking on their abdomen. However, the brown widow's coloration can range from a dark brown to tan, and the hourglass is orange, not red.

Brown widows are considered some of the most venomous spiders, due to their venom being twice as poisonous as that of black widows, but they don't inject very much when they bite, and serious complications are even rarer than bites.

In the United States, many people worry unnecessarily about the fangs of the brown recluse (Loxosceles reclusa). You can identify brown recluses by the violin-shaped marking on their abdomens. Brown recluse spiders like their privacy, and will gladly avoid human contact, sticking to small, dark places out of the sunlight.

That said, a brown recluse spider can provide a painful bite, and in extreme cases the toxins in their venom can leave you with significant scarring from tissue breakdown. It's possible that the resulting wound could become infected, and that could result in death, but odds are strongly in favor of your survival.

In reality, our arachnophobia-induced aversion to tarantulas is misplaced. The formidable critter'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 small amount will actually bite humans, and only some of those can inflict any significant harm. 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.

This occurs at every level: People often misidentify a wound or bite they think was caused by a spider, and even when there's a spider in the vicinity, they often fail to correctly identify the species.

A case in point is the brown recluse spider. In one study of 600 hospital patients claiming to have suffered from a brown recluse spider bite in Southern California, doctors could confirm only 20 percent of the bite wounds as coming from the spider [source: UC Riverside].

That said, we've covered a handful of the most dangerous spiders in the world that would be best 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.

Venomous spiders are equipped with a 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 toxins. Not all spider bites are toxic; many spiders give dry bites (without venom) as a warning.

A Respectful Distance Is Wise

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.