Scientists say the Sydney funnel-web spider is one of the few whose bite can kill a person

Few spiders anywhere in the world carry venom capable of killing a healthy adult human, and one of that short list lives in backyards, gardens, and swimming pools across one of Australia’s most densely populated regions. The Sydney funnel-web spider has become a fixture of local folklore precisely because its bite is not just painful but medically dangerous, a rare distinction among the vast majority of spider species, which cannot seriously harm a person at all. Decades of research have identified exactly what makes its venom so unusual, and why the threat it poses today looks very different than it did a century ago.

A Spider Built for Ambush, Not Aggression

Atrax robustus is a shiny, dark brown to black spider that grows to a body length of roughly 2 to 4 centimeters, living in silk-lined burrows tucked under logs and rocks in cool, humid sites, according to the Australian Museum. Around each burrow entrance, the spider spins irregular silk trip-lines that radiate outward like an early-warning system; when a beetle, cockroach, small lizard, or millipede triggers one of those lines, the spider rushes out, subdues the prey with its large fangs, and drags it back into the burrow to feed. The species is concentrated in a band running from the Central Coast south to the Georges River and as far west as Baulkham Hills, with additional records from the Blue Mountains and Wollongong.

Why Only the Males Have Killed

Every recorded human death from a Sydney funnel-web bite has been attributed to a male spider, and the reason comes down to chemistry rather than behavior alone. Male venom contains a unique compound called Robustoxin, also known as delta-Atracotoxin-Ar1, which severely disrupts the nervous systems of humans and monkeys but has little effect on other mammals, according to the museum’s Australian Funnel-web Spiders factsheet. Female spiders lack this component in comparable concentrations, which likely explains why bites from females have not been linked to any deaths, though the museum stresses that any funnel-web bite should still be treated as a medical emergency. Adult males also leave the safety of their burrows during the warmer months, wandering at night from roughly November through April in search of mates, which puts them in far more frequent contact with people than females, which rarely leave their burrows at all.

That wandering habit has an unglamorous side effect: male funnel-webs regularly fall into backyard swimming pools, where they cannot swim but can trap a small bubble of air in the hairs on their abdomen, allowing them to survive submerged for up to 30 hours before finally drowning. Wandering males also turn up inside homes and garages, and sometimes hide in shoes left outdoors overnight. Despite the species’ reputation for aggression, the museum notes that funnel-webs cannot jump, though they can move quickly and will rear up on their hind legs to display their fangs when they feel threatened.

An Antivenom That Ended the Death Toll

The species is believed responsible for most of the thirteen deaths historically attributed to Sydney funnel-web bites, a toll that stopped entirely once an effective antivenom reached hospitals. Dr. Struan Sutherland and his team at the Commonwealth Serum Laboratories developed the antivenom for clinical use in 1981, and no deaths have been recorded since it became available, according to the museum. The venom used in that research, and in ongoing antivenom production, comes from a milking program run by the Australian Reptile Park near Gosford, New South Wales, where captured spiders are kept specifically to supply venom for medical use. The same antivenom has also proven effective against several other dangerous funnel-web species and against mouse spider envenomation.

A Threat Concentrated by Geography, Not Just Biology

Part of what makes Atrax robustus significant is simple population overlap. More than four million people now live in the Sydney metropolitan area, which sits at the center of the spider’s known range, making human encounters with the species far more likely than they would be in a less populated part of Australia, per the museum’s funnel-web factsheet. The first confirmed human death from the species occurred on February 5, 1927, when a toddler in Thornleigh was bitten while apparently trying to handle the spider. In January 2025, researchers determined that what had long been treated as a single, variable species is actually three separate ones: the original Sydney funnel-web, a newly distinguished southern species called Atrax montanus, and a Newcastle-area species called Atrax christenseni, according to a study published in BMC Ecology and Evolution. The reclassification does not change the medical advice for a bite, since all three species are treated as potentially dangerous, but it does mean the spider Sydneysiders have feared for a century turns out to be a small family of related, similarly venomous animals rather than one.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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