What is the deadliest spider in the world?

The Black Widow spider is one of the deadliest spiders in the United States.

If Hollywood were a reliable source of scientific information, then flying spiders would be real, and identifying the world's most dangerous spiders would be a breeze. Furry tarantulas crawl through cinema screens in countless horror, sci-fi and adventure movies, leaving viewers dangling to grab the armrests of their chairs. Can the hero escape quickly to avoid the bite of a ferocious spider?

In fact, our aversion to tarantula phobia is wrong. The bristles of a terrible spider are more irritated than its venom. While a bite from a passive tarantula can cause localized pain, it won't kill you unless you're highly allergic.

Of the nearly 40,000 known spider species, only a fraction can cause any significant pain in humans. In fact, there is not a fully accepted consensus about the world's deadliest spiders, because in general, spiders are not much of a threat to our well-being. At the same time, the number of spider bites is often inflated to be unbelievable. In a study of 600 hospital patients who claimed to have been bitten by brown hermit spiders in Southern California, doctors were only able to confirm that 20 percent of bites came from spiders.

That said, there are a handful of arachnids in the world, and it is in our best interest to avoid them. The overall incidence of venomous spiders remains below 10%, but some of their poisons can cause tissue degeneration, cell death, nausea, and other unpleasant side effects.

Before we learn about the culprits on the list of the world's most dangerous spiders, it may be helpful to understand how these arachnids perform their terrible bites. As you read in How spiders work, poisonous spiders are equipped with a poison gland that contains dangerous chemicals. These glands are connected to a set of fangs that the spider uses to deliver poison to the victim. Fangs usually hide inside the spider's jaw until it feels threatened. When this happens, it releases its fangs, digging them into the victim's body and secreting venom. Not all spider bites can cause injury. Many spiders dry bite without venom as a warning.

Think it wouldn't be scarier than meeting a brown hermit or a black widow on a bad night? Think again.

Two deadly spiders

The Sydney funnel-web spider is often referred to as the deadliest spider in the world, with fangs strong enough to pierce toenails.

In the United States, the biggest concern is the fangs of the brown hermit and black widow. A bite by a brown hermit may leave you with visible scars due to tissue rupture, but your chances of survival are high. You can identify a brown hermit by a violin-shaped mark on the abdomen. According to statistics, Black Widows with red hourglass business cards pose a greater threat to humanity. Before doctors discovered antivenom for the widow spider family, the mortality rate for bite victims was about 5%.

While there is no definitive answer as to what the world's deadliest spider is, experts often put the Sydney funnel web spider, or Atrax robustus, at the top of the list of venomous spiders. Of all spiders, this arachnid has caused the most bites and human deaths. Since fangs are strong enough to penetrate fingers and toenails, in extreme cases, a funnel net bite can kill a person within 15 minutes.

As you can infer from its name, the Sydney funnel-web spider is native to Australia and is found within a 99-mile (160-kilometer) radius around Sydney [source: Compendium of Australian Venom]. Humans mostly encounter dark funnel-web spiders during the mating season in summer and autumn, when males leave their burrows in search of females [source: Australian Museum]. However, since the discovery of funnel reticular antivenom in 1980, no one has died from its bite. Behaviorally, funnel-web spiders are more dangerous than black widows or brown hermits because they become aggressive when threatened. If you try to drive one away, it's unlikely to slip away. Male funnel-web spiders are more potentially harmful than female and juvenile spiders – and they are most likely to attack.

The active ingredient in Funnel-web venom is δ-atracotoxin. This chain of amino acids is a neurotoxin that, once in the bloodstream, causes our nerve cells to continuously fire. This rapid shot triggers severe pain at the bite site, which will begin within 28 minutes of the actual bite. In general, spider venom affects humans by interacting with ion receptors in our cells. When this happens, it irritates cells unnaturally, leading to pain and cell dysfunction.

On the other side of the world, the Brazilian stray spider, or Phoneutria nigriven, is usually ranked second, behind the Sydney funnel web, and is the deadliest spider in the world. The 2007 Guinness Book of World Records actually named it the most poisonous spider in the world for its ability to inject 1 to 2 mg of venom into its victims [source: Richards]. You can recognize them by the red hair on their neck. Like funnel-web spiders, Brazilian stray spiders have aggressive tendencies and are known as hunting spiders. Like other spider venoms, the venom of Brazilian stray spiders affects sodium ion receptors, especially in muscle and sensory cells. These spider bites account for about half of spider-related hospitalizations in South America.

Being bitten by any of these spiders can be an unpleasant experience. But today, thanks to the presence of antivenoms, even the most venomous arachnids with the largest and sharpest fangs do not pose much of a health threat to humans. As a rule of thumb, be careful when working in the shady corners of your basement or storage room. Spiders usually do not want to attack, but they defend their territory if necessary.