MOST VENOMOUS SPIDERS: SPECIES, BITES, VENOM, SYMPTOMS

VENOMOUS SPIDERS

spiders in Australia

Almost all of the world's 43,000 known spider species are venomous, but only a handful have venom that affects humans. Some spider venoms make hole in cell membranes causing the cells to die. Most are designed to paralyze prey rather than kill it. That way prey remains fresh until it is eaten. Almost all spider have venoms which affect their prey, but is rarely harmful to humans. The fact that some spider venom is harmful to humans is a coincidence. Among these are the venoms produced by tarantulas, black widows and brown recluses.

Steven Hill wrote in Field & Stream: Of all the creeping, crawling critters that potentially pose problems for humans, spiders occupy a special niche. Unlike the biting, stinging pests such as hornets, wasps, snakes, and ticks that people encounter mostly while outdoors, spiders are just as likely to be found indoors, in our homes and camps. And, while the popular myth that humans swallow eight spiders a year while they slumber is almost certainly false, that’s cold comfort when a spider scurries out of your sleeping bag at bedtime. [Source: Steven Hill, Field & Stream, October 25, 2023]

Joshua A. Krisch wrote in Live Science: As almost all of Earth's spider species are venomous, it is likely that most people have encountered a venomous spider at one point or another. However, only 25 species are known to have killed or caused serious harm to humans. But even these deadly spiders, with potent venom and fangs primed for piercing skin, are not particularly dangerous to humans. The America's Poison Centers (formerly known as American Association of Poison Control Centers - AAPCC) tracked only one death caused by a spider bite in the U.S. in 2021. Australia, home to some of the most venomous spiders in the world, hasn't reported a single spider bite death since the 1980s. [Source: Joshua A. Krisch, Live Science, May 16, 2023]

"It is incredibly rare to have a deadly spider encounter," said Rick Vetter, a retired research associate with the Department of Entomology at University of California, Riverside, whose research focused on medically important spiders. "Considering all the bad things that could happen to you, if spiders are your biggest concern, then you are living the good life."

Issues with Venomous Spider Bite Statistics

spider bites in Australia,From First Aid Pro firstaidpro.com

The America's Poison Centers has a section for spider bite statistics but it is difficult to access spider bite mortality or morbidity. "A number of human deaths each year are attributed to spiders," Rod Crawford, curator of arachnids at the Burke Museum at the University of Washington in Seattle, told Live Science. "However, from a scientific viewpoint, almost none of these attributions are evidence-based."

Joshua A. Krisch wrote in Live Science: It is exceedingly rare, Crawford explained, for a victim to see a spider on their skin, feel a bite, capture that same spider, and then bring the offending spider to a physician (let alone a spider specialist) for analysis. "Practically all of the 'spider bites' you hear about, including those reported to poison centers originate from the belief that if you didn't see what bit you, it was a spider," Crawford said.

Linda Rayor, a behavioral ecologist at Cornell University who focuses on spiders, echoed this sentiment. "I have spent a surprising amount of time trying to track down the human mortality rate from spiders and it is miniscule," she said. "This isn't reliably reported, but it is clear that not that many people get killed by spiders. The most venomous species don't kill or impact that many people. Black widows cause a lot of bites because they are widely-distributed.

Keeping in mind the flawed nature of spider bite statistics,The Australian Museum claims that about 2,000 people are bitten by redback spiders each year, and that the antivenom to treat funnel-web spider bites has been given to about 100 patients since 1980. American Poison Centers's annual report tracked about 3,500 spider bites in the U.S. in 2021, with about 40 "major" clinical outcomes. Nine of those serious outcomes were attributed to black widows; 29 major outcomes and the only death that year were attributed to brown recluses. There were no spider bite deaths in American Poison Center's 2020 report, which tracked seven "major" black widow bites and 23 "major" brown recluse bites.

This means that the deadliest spiders are, in fact, not very deadly. "True human spider bites of any kind — dangerous or harmless — are vanishingly rare," Crawford said. "Take me as an example: Over a long career I have handled tens of thousands of live spiders with my bare hands. Only three actual bites resulted; none of the three had any significant effect. So when people tell me spiders crawl into their beds at night and bite them while they are asleep, I just roll my eyes." Vetter agreed. "In reality, spiders are way down the list of things to be concerned about."

Venomous Spider Species

The deadliest spiders — or at least those most frequently cited as having caused death or serious injury to humans — are 1) funnel-web spiders (Atrax), 2) redback and black widow spiders (Latrodectus), 3) banana and wandering spiders (Phoneutria) and 4) recluse spiders (Loxosceles). [Source: Joshua A. Krisch, Live Science, May 16, 2023]

A black widow bite can cause severe pain and muscle spasms. Brown recluse venom degrades tissue and produces a gangrene-like wound. Funnel spider venom leads to trembling, increased blood pressure and vomiting. Tarantula venom can inhibit the movement in signal-carrying ions in cell channels, resulting in numbing, paralysis, convulsions, high blood pressure, cardiac arrhythmia. Most victims of black widow or tarantula bites are advised to wash the wound with soap, place ice on it and take aspirin or acetaminophen. Brown spider bites, which attack tissue and cause necrotic lesions, require a trip to hospital.

Joshua A. Krisch wrote in Live Science: The only arachnid genus that gives the funnel-web a real run for its money as the deadliest spider is Latrodectus, which includes the Australian redback (Latrodectus hasselti) and the more familiar black widow spider in the U.S. These spiders have a slight edge because they bite humans more frequently than funnel-web spiders, with comparably potent venom. " [Source: Joshua A. Krisch, Live Science, May 16, 2023]

Funnel Web Spiders — the World’s Deadliest Spiders

Funnel-web spiders are recognized as the deadliest spiders in the world. Native to Australia, their venom contains 40 different toxic proteins, according to Mount Sinai School of Medicine. These spiders have been responsible for several human deaths in the Sydney area, but no deaths have been reported from funnel-web spiders in Australia since 1980. [Source: Olivia Munson, USA TODAY, February 26, 2023]

Michelle Starr wrote in ScienceAlert: Almost every Australian is taught, from a very young age, to be cautious around the funnel-web spider. These large, black, aggressive arachnids can be found along the eastern coast of the continent, making their homes in web-lined burrows, to pounce on the small critters on which they feast. They also, through some quirk of evolution, secrete a venom more deadly to humans than any other spider. There are dozens of funnel-web species in Australia, but the most venomous of the bunch is the Sydney funnel-web (Atrax robustus). The bites of six of funnel-web spider species have caused severe injuries to victims. The bites of northern tree-dwelling funnel-web spiders (Hadronyche formidabilis) are also potentially deadly, [Source: Michelle Starr, ScienceAlert, January 18, 2025]

Funnel-web spiders in Australia, sometimes called atracids, belong to the Atracidae family of mygalomorph spiders (which includes trap-door spiders and tarantulas). Atracidae consists of three genera: Atrax, Hadronyche, and Illawarra, comprising 35 species. Spiders in the atrax genus have been described as being "very large, very poisonous, very aggressive." They can lunge at prey or in self defense. The bite can be very painful. Symptoms include muscle spasms (twitches) profuse sweating, high blood pressure, fluid in lungs, coma." Death when it has occurred has been caused by asphyxiation. Funnel-web spiders can be 10 centimeters (four inches long). Their fangs can penetrate leather boot. It took 20 years to developed an anti-venom.

Recluse Spiders

Loxosceles spiders, the most familiar of which is the brown recluse (L. reclusa) found in the U.S., may be one the most common causes of spider-related injuries, with painful bites that can cause body aches and fever and take months to fully resolve. But they are very rarely deadly. Recluse spiders are also known as brown spiders, fiddle-backs, violin spiders, and reapers, They are venomous spiders whose bite, which sometimes produces a characteristic set of symptoms known as loxoscelism, in which a dusky, shallow open sore forms as the skin around the bite dies (necrosis). It is the only known spider type that causes necrosis in humans.

The Chilean recluse spider is regarded as the world’s third most venomous spider. As its name suggests, it is mainly found in Chile but it also has been seen in some parts of the U.S. and in Brazil. The bite can cause tissue damage which can take months to heal and can leave behind visible scars. In very rare cases, the toxins from a bite can lead to kidney failure and, very occasionally, can result in death. Chilean recluse spider are very similar to brown recluse spiders, the world’s fourth most venomous spider. They primarily reside in North America, and quite shy and retiring as their name suggests. You aren't likely to be bitten by one unless you accidentally step on it or touch it.

Steven Hill wrote in Field & Stream: The venom of a brown recluse (Loxosceles reclusa) contains a protein that attacks the cell membranes in tissue, destroying the walls of blood vessels. A bite that starts as a small white blister can grow into a large skin ulcer that takes several months to heal. Fatalities, which are rare, are usually caused by an infection created by these slow-healing wounds, so getting medical attention is key. While commonly found throughout the Midwest and South, brown recluses are thought to be over-reported, since they can often be mistaken for other spider species. The distinctive feature of the brown recluse is the dark fiddle-shaped marking on its back that gives it the common name “violin spider.” Recluses, as the name implies, go out of their way to avoid a confrontation. In fact, they cannot bite humans, the CDC reports, “without some form of counter pressure, for example, through unintentional contact that traps the spider against the skin.” [Source: Steven Hill, Field & Stream, October 25, 2023]

Wandering Spiders

Phoneutria spiders, the most common of which are often referred to as banana spiders or wandering spiders, are native to Brazil and have the most neurologically active venom of any spider. Wandering spiders They get their name from their nighttime visits to the jungle floor to find prey. A wandering spider (family Ctenidae) usually consumes katydids on the forest floor in the rainforests of South America. Spider bites from this species are dangerous yet rarely fatal because of the small quantity of venom injected and available antivenom treatments.

The Brazilian wandering spiders is regarded as the world’s second most deadly venomous spider. It can grow up to five centimeters in body length, roughly the length of an adult's index finger, making them relatively big for a spider. During the day, they like to hide in banana plants and can find their way into banana shipments that travel to other parts of the world. They sometimes take shelter in the nooks and crannies of houses or cars and administer a nasty bite if threatened or touched. Females have more toxic venom than males, and a bite can lead to raised blood pressure, fever, vomiting, sweating and breathing difficulties. In some extreme cases, it can lead to paralysis, respiratory arrest and death, if left untreated.

Joshua A. Krisch wrote in Live Science: Phoneutria spiders, the most common of which are often referred to as banana spiders or wandering spiders, are native to Brazil and have the most neurologically active venom of any spider. But they rank a bit lower on the list of the world's deadliest spiders because their venom works relatively slowly, leaving ample time for treatment. [Source: Joshua A. Krisch, Live Science, May 16, 2023]

Australian Redback Spiders

Australian redback spiders (Latrodectus hasselti) are regarded by some reckonings as the world’s fifth most venomous spider. They are black with a red stripe on their back, and are less than five centimeters (two inches) in length and have a one centimeter (half inch) body. They produce venom equivalent to a bad bee sting that in some cases makes people sick for a couple of days. [Source: Kevin Sullivan and Mary Jordan, the Washington Post]

According to the Australian Museum about 2,000 people are bitten by redback spiders each year. No one has died from a redback bite in Australia since an antivenom was developed in 1956. Redbacks are very common and few people have ever been seriously hurt by them. They are often found in wood piles and garden sheds. A popular schoolyard goes" "There was a redback on my toilet seat when I was there last night. I didn't see it in the dark, but boy I felts its bite.”

Redback spiders are members of the global spider genus Latrodectus, the widow spiders, which also include black widow spiders. Female redback spiders live for two to three years while males only live for about six to seven months. The male’s lifespan is cut short by sexual cannibalism during mating, male-male competition, and size differential between males and females (often leading to females killing the much smaller males).[Source: Aaron Bindman, Animal Diversity Web (ADW) |=|]

Redback spiders are aposematic, meaning that their red markings warn predators that they are venomous. Few species prey on redbacks other than daddy longlegs, white-tailed spiders and parasitoid wasps. The primary ecosystem role of redback spiders is as an insect predator. They have adapted well to human-altered environments.

Black Widow Spiders

The black widow spider (Latrodectus Hesperus) can be identified by a red hourglass marking on it belly. Its venom is reportedly 15 times stronger than a rattlesnake’s. Still death is rare in part because the amounts of venom the spider injects is relatively low. Symptoms include chills, breathing difficulty and muscle cramps. An antivenin has been developed. Widow spiders get a bad rap for their bites, which can be very painful to humans but rarely cause death. The species like to weave their haphazard cobwebs in urban and suburban environments and often come into contact with humans

Black widows account for more than 2,500 visits to U.S. poison control centers annually. They are usually found in dark and undisturbed places, Most black widow bites occur when people inadvertently disturb their webs, which can be found under stones, in stumps in dark corners of barns basements, and and garages and other undisturbed cavities, such as vacant animal burrows. They like outdoor toilets because they attract flies, the spider’s favorite prey

Steven Hill wrote in Field & Stream: The A black widow bite is distinctive for the two puncture marks it leaves in the skin. The bite may feel like a pinprick, but the neurotoxin it injects can spread from the bite area to the chest, abdomen, or the rest of the body, where it can cause severe muscle pain and cramping, nausea, and breathing difficulty. Despite its reputation as a potential killer, no U.S. fatalities have been attributed to black widows for decades, and most bite victims recover without serious complications. A black widow can be identified by the distinctive red pattern on its underside. [Source: Steven Hill, Field & Stream, October 25, 2023]

Matt DiSanto wrote: Black widow bites come primarily from adult female spiders, and especially those protecting an egg sac, Penn State Extension notes. At first, bites appear painless before symptoms arrive an hour or two later, usually including any of the following: nausea, chills, slight fever, raised blood pressure, retention of urine, burning sensation of the skin, fatigue, motor disturbances, breathing difficulty, constipation and muscle aches, particularly in the abdomen. [Source: Matt DiSanto, State College Centre Daily Times, October 25, 2023]

“Small children and the elderly are more susceptible to the venom due to their smaller body mass or generally frailer condition, so are more likely to have adverse or severe effects,” Skvarla wrote. “So, a bite is certainly not a pleasant experience, but it’s usually not as bad or threatening as most people perceive them to be.” Though a rare black widow bite is frightening, it is unlikely to turn fatal, researchers say. The 2021 National Poison Data System report from America’s Poison Centers reported zero fatalities following 1,004 black widow bites. Some people may wind up facing more complications from an allergic reaction to antivenin — a treatment for black widow bites developed from horse serum — than a bite on its own, Skvarla wrote.

According to Gizmodo: Black widow spiders across the southern United States are getting eaten up by brown widows, their lesser-known cousins, according to research investigating the relationship between the two arachnids. Three species of black widow are native to the United States; brown widows are believed to be native to Africa but are now present on all continents but Antarctica. [Source: Isaac Schultz, Gizmodo, March 13, 2023]

While black widows are a shy spider species — only getting aggressive when they are pinched or pressed — brown widows seek out black widows to bite. Bit(e) by bit(e), in a pattern first noticed a decade ago, the black widow spiders are being displaced by the interlopers according to a study published in March 2023 in the Annals of the Entomological Society of America by a team led by spider biologist Louis Coticchio.

Avoiding Spider Bites and What Do If Bitten

Steven Hill wrote in Field & Stream: Most spiders you’re likely to encounter would much rather escape than attack, and your odds of running into serious trouble due to a spider bite are low. Still, an ounce of prevention, as the saying goes, beats a trip to the emergency room. [Source: Steven Hill, Field & Stream, October 25, 2023]

1) To avoid direct contact with spiders, use gloves when moving firewood or cleaning out long-undisturbed sites like storage sheds or camp cabins.

2) Inspect or shake out any clothing, shoes, towels or bedding before use, and consider storing clothing or outdoor equipment in tightly closed plastic bags.

3) Shake out your boots before slipping them on for that late-night outhouse run. A trapped spider is a dangerous spider.

4) Keep your tetanus shot up to date. According to the CDC, spider bites can become infected with tetanus spores. If you haven’t had one in the last ten years, it’s time for a booster.

5) If you do get bitten, wash the bite area with soap and water, then apply ice to reduce swelling. Consider seeking medical attention if symptoms are serious or if you know you’ve been bitten by a venomous spider.

6) According to the University of Melbourne: Most bites occur in the warmer months, and are predominantly sustained on the extremities. The pressure immobilisation method of first aid should be employed for bites by any spider.

Image Sources: Wikimedia Commons

Text Sources: Mostly National Geographic articles. Also David Attenborough books, Livescience, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, and various books and other publications.

Last updated August 2025