Redback Spider (Latrodectus hasseltii)
Australia's best-known venomous spider is barely the size of a pea. The redback lives in sheds, letterboxes, garden furniture and rubbish piles across the continent, and the adult female's red dorsal stripe is one of the few spider markings almost everyone recognises. Its bite is genuinely medically significant, yet no confirmed death has been recorded in Australia since antivenom became available in 1956.
By Dr. James WatuwaPublished September 26, 2019Updated September 13, 2026✓ Reviewed by Dr Richard J. Pearce (PhD)
In this guide
Physical description and identification
Almost everything people picture when they hear the word redback belongs to the adult female: a pea-sized, lacquer-black abdomen with a broad red to orange stripe on top and a red hourglass underneath. The male is so different in size and pattern that most Australians have never knowingly seen one, and that gulf between the sexes is itself a useful clue.
Adults
- Size: a mature female is about 10 mm (0.4 in) in body length with a leg span near 30 mm — a spider that sits on a fingernail. Males are dwarfs at 3–4 mm, roughly the length of a grain of rice.
- Colour: the female has a globular, glossy black abdomen with a red, orange or faded stripe running back toward the spinnerets, and a sharply defined red hourglass below. Immature females look browner and carry extra white streaks that fade with age. Males are pale fawn with white bars, small red patches and a weak hourglass.
- Eyes and fangs: eight small eyes in two rows of four. Vision is poor and the spider reads its world through vibration, as explained in our guide to spider eyes. A female can puncture human skin; a male very rarely can.
- Distinctive features: a comb of stiff curved bristles on the hind legs lets the spider fling gluey silk over prey from a safe distance instead of grappling with it. It habitually hangs upside down beneath the tangle of its web.
Eggs and egg sacs
The female hangs round, creamy white sacs about 10 mm across in the upper part of her web and guards them closely. A sac usually holds 40 to 250 eggs, and a well-fed female may build eight to ten of them, one every one to three weeks in warm weather. She stores sperm from a single mating and can keep laying fertile sacs for up to two years — one reason a single introduced female can found a population.
Spiderlings
Eggs hatch after about eight days in summer. Hatchlings stay sealed in the sac for another week, living on yolk and moulting once before chewing their way out. They are pale grey with dark speckling, and sibling cannibalism inside a crowded sac is common. After a short spell in the mother's web they climb high, release a silk line and are carried off on the breeze — the method described on our page about spider ballooning. Females mature in three to four months, males in two to three.
The web
The redback builds a gum-footed tangle web, and its architecture explains where the spider is found. A dry funnel retreat sits in the highest sheltered corner of a cavity; from the tangle below, taut vertical lines run to the ground and carry glue only in their last few millimetres. An ant or beetle sticks to a gum foot, the line snaps free under tension, and the prey is hoisted into the air where it has no purchase. Because the design needs a dry roof and a firm floor, redbacks concentrate in exactly the man-made cavities people use for storage. Our overview of spider webs compares this with orb and sheet designs.
Where the redback spider lives
Latrodectus hasseltii is native to Australia and occurs in every state and territory, from tropical Queensland to Tasmania and across the arid interior. It has adapted to urban landscapes so completely that suburban densities far exceed those in undisturbed bushland. It also travels well in freight: established populations now exist in New Zealand, where it competes with the native katipo, and in Japan, where it was found around the port of Osaka in 1995 and has since spread through several prefectures. Records from the United Arab Emirates and from European cargo mostly represent hitchhikers rather than breeding colonies.
Habitat preference is simple: dry, dark, sheltered and undisturbed, with a solid surface below. Typical sites are the underside of garden furniture and barbecues, letterboxes and meter boxes, rubbish and timber piles, sheds, machinery, roof cavities, rock crevices, hollow logs and the rims of outdoor toilets. Redbacks rarely settle deep inside a heated house the way the common house spider does, preferring the outer edges of buildings and the clutter of a garage.
Are redback spiders venomous?
Yes, and seriously so. The redback is one of the few Australian spiders whose bite is genuinely medically significant, which is why it appears on most lists of the country's most venomous spiders. Its venom contains alpha-latrotoxin, the presynaptic neurotoxin found throughout the genus Latrodectus. It forces nerve endings to release their neurotransmitters all at once, so the resulting illness — latrodectism — produces pain, sweating and autonomic upset rather than the tissue destruction of a recluse bite.
Two qualifications matter. Only the adult female reliably has fangs long enough to pierce human skin. And the spider injects a very small volume of venom and frequently bites dry, so many encounters cause nothing worse than brief local pain. Potency and probability are different things.
Can redback spiders bite?
They can, and the redback accounts for more bites requiring assessment in Australia than any other spider. Almost all happen when a female is pressed against skin: reaching into a stored box, pulling on a glove or boot left in a shed, lifting a pot, or sitting on unused outdoor furniture. The spider does not chase or leap.
A bite feels like a sharp pinprick, and often little follows. When venom is injected, pain builds over five minutes to an hour and radiates up the limb. Characteristic features are local pain out of all proportion to the tiny puncture, sweating often confined to the bitten limb, goose bumps, nausea, vomiting, headache, abdominal or chest pain and raised blood pressure. Symptoms usually peak within hours, but untreated pain can wax and wane for days. Children, older adults and people with heart disease are more vulnerable, and no redback bite in a child should be managed at home.
What to do after a suspected redback bite: wash the area with soap and water and apply a cold pack. Do not use a pressure immobilisation bandage — that is the first aid for funnel-webs such as the Sydney funnel-web, and on a redback bite it traps venom and worsens pain. Do not cut, suck or apply heat or alcohol. Photograph the spider if you safely can, and go to hospital or call the poisons centre if pain spreads, if sweating or vomiting develop, or if the person bitten is a child. Treatment is mainly strong analgesia and observation; antivenom exists for severe cases, although the randomised RAVE-II trial published in 2014 found it barely outperformed placebo, so clinicians now use it more selectively.
Pets are at risk too. Cats are notably more susceptible than dogs, and a cat with pain, tremor, drooling or hind-limb weakness after time in a shed should see a vet promptly.
Ecological importance and behaviour of the redback spider
The redback is a sedentary ambush predator that may spend its whole adult life in one web. Prey is whatever meets the gum feet: ants, beetles, cockroaches, crickets, slaters and other spiders, including trapdoor spiders. There are verified records of small lizards and even juvenile snakes hoisted and killed in redback webs — a consequence of the web's lifting mechanism rather than unusual strength.
Mating and sexual cannibalism: during copulation the tiny male somersaults his abdomen into the female's fangs. She begins to digest him while insemination continues, which fertilises more eggs and makes it harder for rivals to displace him. Males can avoid this entirely by mating with subadult females through the not-yet-hardened exoskeleton, a tactic confirmed by researchers in 2016.
Natural predators: daddy-long-legs and other cellar spiders invade redback webs and kill the occupant, and the black house spider takes wandering juveniles. The specialist wasp Agenioideus nigricornis paralyses adult females for its larvae, while mantid lacewings and parasitoid wasps attack the egg sacs.
Seasonal behaviour: redbacks are active all year in warm regions, but numbers and bite reports peak from November to March. In cooler southern areas activity drops in winter and juveniles shelter in cavities, as covered on our page about where spiders go in the winter.
Relationship with humans: the species is both a real hazard and an effective urban pest controller. Wear gloves when moving stored items, shake out boots and gloves, check under outdoor furniture, and clear webs with a stick or vacuum rather than a bare hand.
Similar spiders and how to tell them apart
| Spider | How it differs from the redback |
|---|---|
| Black cobweb spider (Steatoda capensis) | The classic false redback. Glossy black or dark brown with at most a thin pale crescent at the front of the abdomen, never a long red stripe or a red hourglass. Its bite is mild. |
| False black widow (Steatoda grossa) | Similar shape but purplish brown with pale chevrons instead of black with red. Common in houses; the bite causes short-lived local pain only. |
| Southern black widow (Latrodectus mactans) | A true widow with the same venom chemistry, but plain glossy black above with no dorsal stripe, and North American rather than Australian. |
| Brown widow (Latrodectus geometricus) | Mottled tan to grey-brown with banded legs and an orange hourglass, and its egg sacs are covered in silk spikes rather than smooth. |
| White widow (Latrodectus pallidus) | Pale cream to sandy widow of arid North Africa and the Middle East, with no red markings at all. |
| Noble false widow (Steatoda nobilis) | Brown with cream chevrons and reddish legs, and largely European. No stripe, no hourglass and a far less severe bite. |
Quick facts
| Other names | Red-back spider, Australian black widow, jockey spider |
|---|---|
| Distribution | Native and widespread across Australia; established in New Zealand and Japan, with scattered freight records elsewhere. |
| Habitat | Dry sheltered cavities: sheds, letterboxes, meter boxes, garden furniture, machinery, rubbish and timber piles, rock crevices and hollow logs. |
| Diet | Ants, beetles, cockroaches, crickets, slaters and other spiders; occasionally small lizards caught by the gum-footed lines. |
| Lifespan | Females two to three years; males usually only months after maturing, and far less if they mate. |
| Predators | Cellar spiders, black house spiders, the wasp Agenioideus nigricornis, mantid lacewings, parasitoid wasps, birds and lizards. |
| Web | Gum-footed tangle web with a dry funnel retreat above and sticky vertical trap lines anchored to the ground. |
| Danger | Medically significant. Female bites cause latrodectism; antivenom is available and no confirmed death has occurred in Australia since 1956. |
| IUCN status | Not evaluated. Abundant and expanding in urban habitats. |
Did you know?
- The species was described in 1870 by the Swedish arachnologist Tamerlan Thorell and named after the Dutch naturalist Johan Coenraad van Hasselt.
- Redback antivenom, introduced in 1956, was the first spider antivenom produced in Australia and is still one of very few in the world.
- Slim Newton's comic song The Redback on the Toilet Seat won a Golden Guitar at the Country Music Awards of Australia in 1973, and South Australia's state cricket team plays as the Southern Redbacks.
- Because a female stores sperm for up to two years, one mated spider hidden in a shipping container is enough to found an overseas population — which is how the species reached Japan.
In summary, the redback is a small, sedentary spider with a bite that deserves respect but not panic. Learn the female's red stripe and her upside-down posture in a gum-footed web, keep gloves on when moving stored clutter, and treat spreading pain or sweating after a bite as a reason to get medical assessment rather than to wait it out.
Frequently asked questions about the redback spider
What does a female redback spider look like?
An adult female has a glossy black, pea-shaped abdomen about 10 mm long carrying a bold red or orange stripe on top and a sharply defined red hourglass underneath. Her legs are black, thin and slightly clubbed, and she normally hangs upside down beneath an untidy tangle of silk.
How can you recognise a male redback spider?
Males are tiny, only 3 to 4 millimetres long, and pale fawn to light brown rather than black. They carry white bars and small red patches on the abdomen, swollen boxing-glove pedipalps and a faint hourglass below. Their fangs rarely penetrate human skin.
How big does a redback spider get?
A female's body reaches roughly 10 mm with a leg span near 30 mm, so the whole spider sits on a fingernail. The male is about a third of her length and a tiny fraction of her weight, one of the most extreme size differences between sexes in any spider.
How many eggs does a redback spider lay?
Each round white sac holds roughly 40 to 250 eggs, and a well-fed female may build eight to ten sacs over her life, adding a new one every one to three weeks in warm weather. She stores sperm from one mating and can keep producing fertile sacs for up to two years.
How do baby redback spiders spread?
Spiderlings hatch after about eight days, stay inside the sac for another week while they use up the yolk and moult once, then leave the mother's web. Most disperse by ballooning: they climb to a high point, release a thread of silk and let the wind carry them to a new site.
What kind of web does a redback spider build?
It builds a gum-footed tangle web. A dry funnel retreat sits high in a sheltered corner, and taut vertical lines run from the tangle to the ground with glue only at their tips. A crawling insect sticks to a line, the line snaps free and the prey is hoisted into the air.
Is a redback spider bite dangerous to humans?
Yes. The female's venom contains alpha-latrotoxin and can cause latrodectism: intense spreading pain, sweating, goose bumps, nausea, vomiting, headache and raised blood pressure. Most bites are mild, but any bite with spreading pain, sweating or vomiting, and any bite in a child, needs medical assessment.
What first aid should you give for a redback bite?
Wash the area, apply a cold pack for pain and get medical advice. Never use a pressure immobilisation bandage, which is the first aid for funnel-web bites and makes redback pain worse. Do not cut, suck or apply heat. Photograph the spider if it is safe to do so and go to hospital if symptoms spread.
Where are redback spiders most often found around a home?
In dry, dark, undisturbed cavities with a firm floor: under garden furniture and barbecues, inside letterboxes and meter boxes, in sheds, garages, machinery, stacked timber, rubbish piles and rock crevices. They rarely settle deep inside a heated house the way common house spiders do.
Are redback spiders found outside Australia?
Yes. Breeding populations are established in New Zealand and in Japan, where the spider was first found near Osaka in 1995 and has spread through several prefectures. It has also been intercepted in the United Arab Emirates and in freight arriving in Europe, usually as a hitchhiker rather than a colony.
References
- World Spider Catalog (2026). Latrodectus hasselti Thorell, 1870. Natural History Museum Bern. wsc.nmbe.ch/spec-data/45672/taxon
- Isbister, G. K. et al. (2014). Randomized controlled trial of intravenous antivenom versus placebo for latrodectism: the second Redback Antivenom Evaluation (RAVE-II) study. Annals of Emergency Medicine 64(6): 620–628. doi.org/10.1016/j.annemergmed.2014.06.006
