Atrax
Atrax is a small genus of glossy black Australian mygalomorphs that contains the single most notorious spider on earth, the Sydney funnel-web. Its members dig silk-lined burrows in cool, damp ground in the southeast of the continent, and the males carry a venom whose key toxin is almost uniquely lethal to primates while leaving most other mammals unharmed.
By Dr. James WatuwaPublished September 11, 2019Updated September 13, 2026✓ Reviewed by Dr Richard J. Pearce (PhD)
In this guide
Physical description and identification
Atrax is one of three genera in the family Atracidae, the Australian funnel-web spiders, alongside the much larger Hadronyche and the monotypic Illawarra. It is a compact group of ground-dwelling mygalomorphs restricted to southeastern Australia, and by far its best-known member is the Sydney funnel-web, Atrax robustus.
The genus has a tangled taxonomic past that is often reported wrongly. Atracine funnel-webs were first placed with the curtain-web spiders (Dipluridae), were moved in 1980 into Hexathelidae as the subfamily Atracinae, and were finally raised to their own family, Atracidae, by a phylogenomic study published in 2018. For most of the last century three Atrax species were recognised — A. robustus, A. sutherlandi and A. yorkmainorum; a 2025 revision of the Sydney funnel-web complex resurrected one older name and described a large new species from the Newcastle district, taking the total to five.
Adults
- Size: adults run from about 15 mm to roughly 40 mm in body length. Females are consistently heavier and bulkier; males are smaller, longer-legged and more angular. A. sutherlandi is the largest.
- Colour: uniformly dark — blue-black, jet black, dark brown or plum. There are no bands, spots or chevrons. The carapace is essentially hairless and glossy enough to catch the light; the abdomen is matt and finely haired.
- Eyes: eight small eyes grouped tightly on a raised mound at the front of the carapace, all much the same size. Useful detail is only visible with a lens; see our guide to spider eyes.
- Spinnerets and fangs: the rear spinnerets are long, soft and finger-like and project clearly beyond the abdomen. The fangs are paraxial, hinged to strike downwards rather than inwards, and they are large enough in a mature female to pierce a fingernail.
- Males: mature males carry a mating spur on the second leg and swollen pedipalp bulbs. Species identification within the genus rests almost entirely on the male palp and spur, so a female or a juvenile usually cannot be named beyond locality.
Eggs and egg sac
Females lay around 100 pale yellow to yellowish-green eggs in a flattened silk sac kept deep inside the burrow. The mother guards and tends it and does not carry it about, so a sac is essentially never found outside a tunnel.
Spiderlings
Hatchlings stay in the maternal burrow for several weeks and through their first moults before dispersing on foot — these spiders are far too heavy to balloon. Juveniles dig their own small burrows close by, so a suitable gully or garden bed can hold a dense cluster of related animals. Maturity takes years rather than months.
The burrow and trip lines
The popular description of Atrax waiting at the narrow end of a funnel-shaped snare is misleading. These spiders do not build a capture web at all. Each one digs a silk-lined tube, often 20–60 cm deep, in moist shaded ground, finishes the mouth with a collar of silk shaped like a shallow funnel, a T or a Y, and lays a few irregular trip lines across the surrounding soil. Vibration on a line brings the spider out in a fraction of a second. Contrast this with the flat horizontal sheets built by the unrelated funnel weavers, and see spider webs for the wider picture.
Where Atrax spiders live
The genus is endemic to southeastern Australia and occupies a much smaller area than its fame suggests. Atrax robustus is confined to the Sydney basin and its margins, from the Central Coast and Newcastle south to the Illawarra and Nowra and west to the lower Blue Mountains. A. sutherlandi occupies the cooler, wetter forests of the southern tablelands and the NSW–Victorian highlands, and A. yorkmainorum occurs around the Australian Capital Territory and the southern tablelands.
No Atrax species lives in Queensland, South Australia, Western Australia or Tasmania. Funnel-webs from those states belong to Hadronyche, which is spread far more widely, from southern Queensland to Tasmania and South Australia.
Habitat is consistent across the genus: cool, humid, shaded ground with something to tunnel under. Sandstone outcrops, wet and dry sclerophyll forest, rainforest margins, deep leaf litter, fallen logs, rockeries, compost heaps and mulched garden beds all qualify, and Sydney suburbs on sandstone country hold some of the highest densities recorded anywhere.
Are Atrax spiders venomous?
Yes, and the genus contains the clearest case in the spider world of a venom that can kill a healthy adult human. The active component of male Atrax robustus venom is a short peptide historically called robustoxin and now named δ-hexatoxin-Ar1a. Homologous toxins occur in the other species; A. sutherlandi produces a close equivalent.
These peptides act on voltage-gated sodium channels in nerve terminals, delaying the channels from closing so that nerves fire over and over. The result is an uncontrolled release of acetylcholine and catecholamines, producing the sweating, salivation, muscle twitching, racing heart and steeply raised blood pressure that define serious funnel-web envenomation.
Two qualifications matter. The toxin is extraordinarily selective for primates: rabbits, cats, dogs and most other mammals survive doses that would be lethal to a person because their blood carries neutralising factors that humans lack. And within each species the male venom is several times more toxic to primates than the female's, which is why the wandering male is the animal that causes serious cases. Atrax is deservedly listed among the most venomous spiders in the world.
Can Atrax spiders bite?
They can, and they are quick to do so when cornered. A disturbed Atrax rears onto its hind legs, raises its front legs and palps and holds its fangs high with venom visible on the tips. It then strikes downwards with force, often more than once, and may hold on. Bites are immediately painful and normally leave two clear puncture marks.
Symptoms. Severe local pain comes first. Systemic envenomation, when it develops, usually begins between about ten minutes and two hours after the bite: tingling around the mouth, twitching of the tongue and other muscles, drenching sweat, heavy salivation, watering eyes, nausea, vomiting, abdominal pain, a fast pulse and high blood pressure, progressing in untreated severe cases to low blood pressure, fluid on the lungs and coma. Small children deteriorate fastest.
First aid. Funnel-webs are one of the few bites where pressure immobilisation is the correct response. Keep the patient still and call emergency services (000 in Australia) immediately. Bandage firmly over the bite with a broad elastic bandage, then wrap the entire limb from the digits upwards, and splint it so it cannot bend. Do not wash the bite, cut it, suck it or apply a tourniquet. If it can be done safely, contain the spider for identification.
Antivenom. Funnel-web antivenom, produced in rabbits and released in 1981, neutralises the venom of both Atrax and Hadronyche and is given intravenously in hospital. Thirteen deaths were recorded before it existed and none has been recorded since. It works only if the patient reaches hospital, so the bandage-and-ambulance sequence is what actually saves lives.
The look-alike that matters: a mouse spider (Missulena) is glossy, black and stocky like an Atrax, but its head is broad and bulbous, its spinnerets are short rather than finger-like, and males often carry a red or bluish patch. Its bite can also be serious, and funnel-web antivenom is effective against it, so the same first aid applies to either animal.
Ecological importance and behavior of Atrax spiders
Atrax spiders are sedentary ambush predators with very small territories. A female may occupy one burrow for a decade or longer, enlarging it as she grows and leaving only to sit at the entrance after dark with her front legs resting on the trip lines. She does not hunt on the move.
Diet: beetles, cockroaches, crickets, millipedes, slaters and snails, with large females occasionally taking a skink or a small frog. Because atracids are abundant in leaf litter across their range, they remove a substantial volume of ground invertebrates every season.
Natural predators: centipedes and scorpions kill them underground, parasitic wasps paralyse and provision them for their larvae, and birds, bandicoots, antechinuses and reptiles pick off wandering males. Those males, moving in the open on humid nights, are the most exposed stage in the life cycle.
Seasonal behaviour: activity peaks in the warm, wet months. Males mature after several years, abandon the burrow permanently and survive only a few months as they search for females. Females live on for many years and produce several egg sacs, which makes Atrax one of the longer-lived spider genera — see how long spiders live for comparison.
Relationship with humans: risk and benefit sit side by side. These spiders control pest invertebrates in gardens and bushland, and live males handed in by the public supply the venom-milking programme that keeps antivenom in stock. Sensible precautions are simple: gloves and closed shoes when gardening, never reaching blindly under logs or pots, shaking out clothing and footwear left outdoors, and checking swimming pools, since a submerged funnel-web can stay alive for hours on trapped air.
Species in the genus and similar spiders
| Spider | What sets it apart |
|---|---|
| Sydney funnel-web (Atrax robustus) | The type species and the dangerous one people mean. Females 30–35 mm, males about 25 mm; confined to the Sydney basin. Responsible for all thirteen recorded funnel-web deaths. |
| Atrax sutherlandi | The largest member of the genus, dark brown to plum, from the cool wet forests of the southern tablelands and the NSW–Victorian highlands. Named for Struan Sutherland, who developed the antivenom. |
| Atrax yorkmainorum | A smaller species of the Australian Capital Territory and southern tablelands, separable from its relatives chiefly on the structure of the male palp. |
| Hadronyche funnel-webs | The sister genus, far larger and more diverse, ranging from southern Queensland to Tasmania and including tree-dwelling species such as the northern tree funnel-web. Equally dangerous. |
| Mouse spiders (Missulena) | Glossy and black, but with a very broad bulbous head, short spinnerets and often red or blue markings on males. Unrelated family; bites can be serious and respond to funnel-web antivenom. |
| Australian whistling spiders (Theraphosidae) | Much hairier, brown rather than glossy black, and far bigger. Their bite is painful but not life-threatening to people. |
Quick facts
| Rank and authority | Genus Atrax O. Pickard-Cambridge, 1877; family Atracidae, infraorder Mygalomorphae. |
|---|---|
| Species | Three recognised for most of the twentieth century; a 2025 revision of the Sydney funnel-web complex raised the total to five. |
| Distribution | Southeastern Australia only: New South Wales, the Australian Capital Territory and eastern Victoria. |
| Habitat | Cool, humid, shaded ground — sandstone crevices, forest leaf litter, under logs and rocks, rockeries, compost and mulched beds. |
| Shelter | Silk-lined burrow with a funnel-, T- or Y-shaped collar and surface trip lines. No aerial capture web. |
| Diet | Beetles, cockroaches, crickets, millipedes, slaters and snails; occasionally small skinks and frogs. |
| Lifespan | Females many years, sometimes well over a decade; males die within months of maturing. |
| Danger | High. Bites are a medical emergency requiring pressure immobilisation and hospital treatment; antivenom has been available since 1981. |
| IUCN status | Not evaluated. Locally common, but urban expansion removes the shaded, humid ground the genus depends on. |
Did you know?
- The genus was erected in 1877 by Octavius Pickard-Cambridge, the English clergyman who described more than 1,500 spider species in his lifetime.
- Atrax sutherlandi is named after Struan Sutherland, the Melbourne researcher whose team produced funnel-web antivenom and who also devised the pressure immobilisation first-aid technique now used for snake and funnel-web bites alike.
- The venom that makes the genus notorious is also a research goldmine: funnel-web peptides are being studied as candidate drugs for stroke and heart attack, and insect-selective relatives are in development as biological pesticides.
- Atracids can survive submerged for hours by trapping a film of air among their body hairs, which is why a funnel-web at the bottom of a pool is often still alive.
- Despite the shared common name, Atrax is not related to the harmless northern-hemisphere funnel weavers; the resemblance is limited to the funnel-shaped silk at the entrance.
In summary, Atrax is a tiny genus with an outsized reputation: a handful of glossy black burrowing spiders in one corner of southeastern Australia, one of which produces the most dangerous spider venom yet described for humans. Identify the hairless carapace, the long rear spinnerets and the reared posture, and treat any bite as an emergency.
Frequently asked questions about the atrax
What does an Atrax spider look like?
Atrax spiders are stocky, dark and completely unpatterned, with a hairless, high-gloss carapace in blue-black, brown or deep plum. Long finger-like spinnerets project from the rear of the abdomen and the fangs hinge downwards. Adults run from about 15 to 40 mm in body length, with females noticeably heavier than males.
How many species of Atrax are there?
Three species were recognised for most of the twentieth century: Atrax robustus, A. sutherlandi and A. yorkmainorum. A 2025 revision of the Sydney funnel-web complex resurrected an older name and described a large new species from the Newcastle area, bringing the accepted total to five.
How venomous are Atrax spiders?
Extremely. Male Atrax robustus venom contains delta-hexatoxin-Ar1a, or robustoxin, which is lethal to primates in small quantities and caused thirteen recorded human deaths before antivenom existed. Bites are medical emergencies. Antivenom released in 1981 has prevented every death since, but treatment must be rapid.
Do Atrax spiders really build funnel-shaped webs?
Not as a snare. Each spider digs a silk-lined burrow twenty to sixty centimetres deep and finishes the entrance with a silk collar that can look like a shallow funnel, a T or a Y. A few irregular trip lines run across the ground and alert the spider to passing prey, which it ambushes.
Where in Australia are Atrax spiders found?
Only in the southeast. Atrax robustus is restricted to the Sydney basin, A. sutherlandi to the cooler forests of the southern tablelands and the New South Wales–Victorian highlands, and A. yorkmainorum to the Australian Capital Territory and nearby tablelands. Funnel-webs elsewhere in Australia belong to the genus Hadronyche.
Are Atrax spiders aggressive towards people?
They are defensive rather than aggressive. A cornered funnel-web rears up, lifts its fangs and strikes hard, sometimes repeatedly, but it does not hunt or pursue people. Almost every bite happens when a wandering male is trodden on, trapped in clothing or picked up, or when someone reaches into leaf litter.
What colour are Atrax spider eggs?
The eggs are pale yellow to yellowish-green and roughly a hundred are laid in a single flattened silk sac. The female keeps the sac deep inside her burrow, tending and guarding it until the spiderlings hatch. She never carries it in her fangs the way a wolf spider carries hers.
What is the correct first aid for an Atrax bite?
Use pressure immobilisation. Keep the person still, call an ambulance, bandage firmly over the bite and then up the entire limb, and splint it so it cannot move. Do not wash, cut or suck the wound and do not use a tourniquet. Safely contain the spider if you can, for identification.
How long do Atrax spiders live?
Females are long-lived for spiders, often holding the same burrow for a decade or more, and some individuals reach around twenty years. Males take several years to mature, then leave the burrow permanently and survive only a few months, dying soon after mating or being eaten while wandering.
Is Atrax the same as a tarantula?
No, although both are mygalomorphs with downward-striking fangs. Tarantulas belong to the family Theraphosidae, are densely hairy, usually brown and far larger, and their bites are painful but not life-threatening. Atrax belongs to Atracidae, is small, glossy and hairless on the carapace, and is medically dangerous.
References
- World Spider Catalog (2026). Atrax O. Pickard-Cambridge, 1877. Natural History Museum Bern. wsc.nmbe.ch/genus-detail/1240/taxon
Other spiders in the Australian Funnel-Web family
All Australian Funnel-Web Spiders →
Australian Funnel-Web SpidersNorthern Tree Funnel-web (Hadronyche formidabilis)
Australian Funnel-Web SpidersSydney Funnel-Web (Atrax robustus)
Australian Funnel-Web SpidersHadronyche
Australian Funnel-Web SpidersHadronyche marracoonda
Actinopodidae SpidersMouse (Missulena)
Desidae SpidersBlack House (Badumna insignis)