Are All Spiders Venomous?

Plenty of people are freaked out by spiders but will take consolation in the fact that most species are harmless to humans. They may be fearsome predators in the insect world, but arachnids generally aren’t a threat to people.

However, this doesn’t mean they can’t bite, or envenomate you.

It may surprise you to learn that almost all spiders are venomous. Only one group of small spiders in the family Uloboridae lack venom glands. Every other spider is capable of injecting venom when they bite you.

But don’t take a flamethrower to your house just yet! Just because most spiders have venom doesn’t mean they can or will use it against you. In fact, only a few species represent a significant threat to people. Among these are the black widow spider, the brown recluse, armadeira spiders and the male Sydney funnel-web.

What are the most venomous spider species?

Nearly every species of spider has venom, but the vast majority are harmless to humans. Most spider bites look just like a regular insect bite, causing raised bumps that may be red, itchy, swollen or painful. Some species, however, are incredibly dangerous and their bites can lead to severe reactions that require medical attention and, in some cases, the administration of antivenom.

The male Sydney funnel-web spider

According to the Guinness World Records, the planet’s most venomous arachnid is the male Sydney funnel-web spider. Native to the state of New South Wales in Australia, this spider has sharp fangs and can deliver a powerful bite. This bite is laced with a highly potent and potentially lethal toxin, which can lead to death in 15 minutes to three days. Fortunately, an antivenom is available and, with modern medical intervention, people rarely die from the bite of funnel webs.

The black widow spider


The black widow is the most venomous spider found in North America and is also native to Australia. Black widow spiders can be recognized by the distinctive, red hourglass-shaped marking on their abdomen.

Though generally not aggressive, they will bite if threatened or disturbed. The bite of the black widow is no more painful than a pinprick, but its venom is highly potent. Within a few minutes of being bitten, pain spreads throughout the entire body of the victim. Further symptoms, including respiratory failure, delirium, vomiting and muscle spasms, develop within a few hours. Fortunately, the bite of the black widow is only fatal in 1% of cases thanks to the existence of an antivenom.

Armadeiras (armed spiders)

Armadeiras (aka armed spiders) are highly venomous spiders native to South America. They are also often referred to as banana spiders, due to their tendency to hide away in banana boxes.

The bite of an armadeira is excruciatingly painful and the neurotoxic venom they inject can cause dizziness, visual disturbances, respiratory failure and, in extreme cases, death. An antivenom does exists but is rarely used; instead, treatment for armadeira bites usually focuses on pain management.

Brown recluse spiders

The brown recluse is another important venomous spider species native to North America and is easily recognizable by the violin-shaped marking on its back. They often hide during the day and, like the black widow, are generally non-aggressive but will attack if disturbed.

People are most often bitten by brown recluse spiders when they don clothes or shoes with the spiders hiding inside them. The bite of the brown recluse is usually painless, but their necrotic venom quickly causes pain and inflammation. Necrosis (death of bodily tissues) starts to spread within a few days of receiving the bite but can be controlled with antivenom.



The tarantula is a popular pet, with all that fuzz, they’re almost cute. These nocturnal, hunting spiders are often tame and can even be handled, but are easily spooked and may still bite. Fortunately, their venom is not considered harmful to humans and a tarantula bite will usually result in nothing more serious than lesions to the skin.

Are all spiders poisonous?

Almost all spiders are venomous, however, very few spiders are poisonous.

Although the two words are often used interchangeably, venomous and poisonous actually mean two different things.

The words “venom” and “poison” both refer to toxic substances created by living organisms. The difference between them is in the way they are delivered. Venom is delivered actively (usually by bite or sting) whereas poison is delivered passively, meaning it is only harmful when eaten or touched.

A venomous spider is one that injects toxins into its victims via a bite, however, a poisonous spider won’t unload its toxins unless you eat it.

Can you tell if a spider is venomous by its coloring?

Unless you’re a (spider expert), determining whether or not a spider is dangerous can be tricky just by looking at it and, unfortunately, the color of the spider is not a reliable indication. A brown spider may be entirely harmless; however, it may also be a venomous brown recluse. Most spiders only bite if they are disturbed or threatened, so the best way to avoid spider bites is to:

  • Check clothes and shoes carefully for spiders before putting them on.
  • If you have to remove a spider from your home, avoid handling it directly. Instead, trap it inside a container before throwing it out of the door/window.
  • If you see an egg sac, approach with caution – some venomous species of spider may attack if they feel their eggs are in danger.
  • Learn to identify any dangerous, venomous spiders in your area so you can recognize them on sight.


Most spider species are venomous, however, only a few of them are dangerous to humans.

The brown recluse, the black widow, the male Sydney funnel-web and Armadeira spiders are among the most dangerous arachnids on the planet. Their bites can cause severe symptoms and even death if left untreated. Fortunately, thanks to modern medicine and the discovery of antivenom, spider bites are rarely fatal to humans.

Frequlently asked questions about venomous spiders

Although all tarantulas are venomous, the toxicity of most tarantula venom is low and therefore generally tarantulas aren't considered to be dangerous to humans.

All widow spiders are highly-venomous therefore should be considered dangerous. But there are also false widow spiders who are much less dangerous. Since false widows look similar to real widow spiders many people fear them. However, although the bite of false widows are also venomous, the venom of these spiders isn't very potent and therefore doesn't pose a threat to human health.

All funnel-web spiders aren't venomous. However, all funnel-web spiders should be regarded with caution since the bite of the venomous funnel-web spiders is highly dangerous to humans.

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