Strictly speaking, no spider is poisonous. Spiders are venomous, and the one whose venom is usually ranked most dangerous to people is the Australian funnel-web, whose bite can kill a human.1PubMed Central. Australian funnel-web spiders evolved human-lethal δ-hexatoxins for defense against vertebrate predators But being deadly in principle and being a real risk today are different things, because a reliable treatment now exists for its bite.2Medical Journal of Australia. Funnel-web spider bite: a systematic review of recorded clinical cases
Why Spiders Are Venomous, Not Poisonous
The two words describe different delivery methods. A poisonous thing harms you when you eat it, breathe it in, or touch it, like some mushrooms.3Burke Museum. Myth: Some spiders are poisonous and others are not. No known spider is harmful that way. Their toxins are proteins that only work when injected.4Burke Museum. Myth: Some spiders are poisonous and others are not. They inject venom through their fangs.5Northwest Exterminating. Venomous vs Poisonous Spiders – What’s the Difference?
Some pest-control sites claim most spiders are poisonous and only a few are venomous.6Northwest Exterminating. Venomous vs Poisonous Spiders – What’s the Difference? That reverses the definitions. Nearly all spiders have venom, and very few can harm a person. People asking about the most poisonous spider almost always mean which bite is most dangerous, so that is the question this article answers.
The bite itself works much like a hypodermic needle. Venom is made in glands connected to the fangs, and the spider pushes it through a channel in each fang into its victim. The spider controls how much it pushes out, which is why a bite can deliver a large dose or almost none.
Tarantulas come closest to harming you by touch: they don’t poison you on contact, but some flick irritating hairs.
The Sydney Funnel-Web Is the Most Dangerous to People
Australian funnel-web venom contains toxins that can cause fatal nerve poisoning in humans.7PubMed Central. Australian funnel-web spiders evolved human-lethal δ-hexatoxins for defense against vertebrate predators The main toxin stops nerve signals from switching off, so nerves keep firing.8PubMed. Characterisation of the effects of robustoxin, the lethal neurotoxin from the Sydney funnel-web spider Atrax robustus, on sodium channel activation and inactivation
People are unusually sensitive to it. Humans and other primates react strongly to funnel-web venom, while dogs, cats and rabbits mostly shrug it off.9Australian Geographic. Funnel-web spiders are Australia’s deadliest? Not for our pets In most animals the nerve gates are shaped so the toxin can’t stick well.10Australian Geographic. Funnel-web spiders are Australia’s deadliest? Not for our pets
That is why “deadliest” depends on who is bitten. Venom strength is often measured in mice, which doesn’t match people.
Funnel-webs live in eastern Australia, and the Sydney species is found around Sydney. Males wander in the warm months and can enter homes and gardens.
A serious bite hurts at once, because the fangs are large. Symptoms can develop quickly, so every suspected bite in Australia is treated as an emergency.
Can a Funnel-Web Bite Still Kill You
Antivenom, a treatment that neutralises the venom, became available for funnel-web bites.11PubMed. Funnel-web spider (Atrax robustus) antivenom in the treatment of human envenomation An illness that once caused death or two to three weeks in hospital became one lasting one to three days.12PubMed. Funnel-web spider (Atrax robustus) antivenom in the treatment of human envenomation There have been no confirmed deaths from funnel-web bites since it arrived.13Medical Journal of Australia. Funnel-web spider bite: a systematic review of recorded clinical cases It fully reversed severe symptoms in 97% of bites where the spider was expertly identified.14Medical Journal of Australia. Funnel-web spider bite: a systematic review of recorded clinical cases It also works against related funnel-web species, not just the Sydney one.15PubMed. Cross-reactivity of Sydney funnel-web spider antivenom: neutralization of the in vitro toxicity of other Australian funnel-web (Atrax and Hadronyche) spider venoms
The venom itself hasn’t become weaker; survival depends on reaching care quickly. For most readers outside Australia, the risk of ever being bitten by one is essentially nil.
After a suspected bite, call emergency services straight away, because symptoms can escalate quickly and treatment is given in hospital. Keep the person calm and still, since movement helps venom travel through the body. Australian first-aid guidance is to apply a firm bandage over the bite and limb and immobilise it, which slows venom spread until care arrives. Don’t delay care to catch or kill the spider; a photo is fine only if it costs no time.
Other Spiders That Can Seriously Hurt People
Black widows attack the nervous system. Their main toxin forces nerve endings to dump their chemical messengers uncontrollably.16PubMed Central. Black widow spider α-latrotoxin: a presynaptic neurotoxin that shares structural homology with the glucagon-like peptide-1 family of insulin secretagogic hormones Bites typically bring pain and muscle cramping rather than skin damage.17PubMed. Mechanisms of alpha-latrotoxin action
Recluse spiders damage tissue. Brown recluse venom contains an enzyme that causes skin and tissue death around the bite.18PubMed Central. A Brief Overview of the Toxic Sphingomyelinase Ds of Brown Recluse Spider Venom and Other Organisms and Simple Methods To Detect Production of Its Signature Cyclic Ceramide Phosphate The same toxins can cause swelling and, more rarely, damage to red blood cells and kidneys.19PubMed Central. Forty Years of the Description of Brown Spider Venom Phospholipases-D Venom strength differs between male and female recluses and between species.20PubMed. Variations in Loxosceles spider venom composition and toxicity contribute to the severity of envenomation
Some spiders outside North America and Australia matter too. Brazilian wandering spider venom contains toxins that can cause a painful, lasting erection in mammals.21PubMed. Erection induced by Tx2-6 toxin of Phoneutria nigriventer spider: expression profile of genes in the nitric oxide pathway of penile tissue of mice Venom of the African six-eyed sand spider caused tissue death and leaky blood vessels in animal tests.22PubMed. Venom of a six-eyed crab spider, Sicarius testaceus (Purcell, 1908), causes necrotic and haemorrhagic lesions in the rabbit Male Australian mouse spiders carry a nerve toxin similar to the funnel-web’s,23PubMed Central. Neurotoxic activity of venom from the Australian Eastern mouse spider (Missulena bradleyi) involves modulation of sodium channel gating and funnel-web antivenom has been effective for mouse spider bites.24PubMed. Spiders of medical importance in the Asia-Pacific: atracotoxin, latrotoxin and related spider neurotoxins
Recluse bites are often misdiagnosed. Many skin wounds blamed on recluses turn out to be bacterial infections or other conditions. Recluses live mainly in the southern and central United States, so a wound elsewhere is very unlikely to come from one. A worsening wound should be examined by a doctor rather than assumed to be a spider bite, since infections need different treatment.
Why Venom Strength Varies Even Within One Species
Venom isn’t fixed. Its strength changes with a spider’s sex and age, and with season and location.25PubMed. Beyond species-level differences: A comprehensive review of intraspecific venom plasticity in spiders In funnel-web and mouse spiders, the wandering males are the dangerous ones.26PubMed Central. Neurotoxic activity of venom from the Australian Eastern mouse spider (Missulena bradleyi) involves modulation of sodium channel gating
Spiders also save their venom. Black widows give a bite with no venom in more than half of defensive encounters.27Animal Behaviour. Poke but don’t pinch: risk assessment and venom metering in the western black widow spider, Latrodectus hesperus Venom is costly for a spider to make.28Animal Behaviour. Poke but don’t pinch: risk assessment and venom metering in the western black widow spider, Latrodectus hesperus They inject about 1.8 times more venom when squeezed on the body than when touched on a leg.29Animal Behaviour. Poke but don’t pinch: risk assessment and venom metering in the western black widow spider, Latrodectus hesperus Pressing a spider against your skin therefore makes a worse bite more likely.
Many people bitten by a dangerous species develop few symptoms because the spider injected little or nothing, but that doesn’t make a bite safe to ignore. If pain spreads, cramps start or other symptoms appear, it should be checked.
Since most bites come when a spider is pressed against skin, avoiding that pressure is the most practical protection. Shake out shoes, gloves and clothing left outdoors or in a garage before putting them on, since a spider hiding there is squeezed when you dress. Wear gloves when moving woodpiles, stones or garden debris, where spiders shelter. If you find a spider on you, brush it off gently instead of slapping it.
Tarantulas and Pet Spiders
Many American tarantulas shed barbed irritating hairs to defend themselves.30PubMed. Urticating hairs in arthropods: their nature and medical significance The barbs can work their way into the eye and cause lasting inflammation.31PubMed Central. On the Dangers of Tropical Spiders as a Pet: A Review of Ocular Symptoms Caused by Tarantula Hairs Hairs can also cling to skin and be rubbed into the eyes, so wash your hands after handling the spider or cleaning its enclosure. Wear eye protection when cleaning, since shed hairs build up there. If an eye becomes red or painful after handling, see a doctor, as embedded hairs can need removal.
Bites from large spiders are a separate matter. Some big Asian tarantulas have strong venom, and their bites can be very painful, though deaths aren’t known. Treat any bite from a pet spider with care, and seek advice if symptoms spread.
Why Spider Danger Is Often Overstated
Nearly half of spider news stories contain errors, and over 4 in 10 are sensationalist.32PubMed. The global spread of misinformation on spiders Exaggerated bite stories also get shared more on social media,33People and Nature. Media framing of spiders may exacerbate arachnophobic sentiments so people come to see spiders as more dangerous than they are.34People and Nature. Media framing of spiders may exacerbate arachnophobic sentiments
When you meet a scary claim, ask whether the spider was actually identified, since most bite stories involve a spider nobody saw or confirmed. Check whether the species lives in that area at all, because many viral claims name spiders that cannot be found there. And remember that the vast majority of spiders cannot hurt people, so a scary headline is rarely about a typical one.