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Spider bite

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Title: Spider bite  
Author: World Heritage Encyclopedia
Language: English
Subject: Loxoscelism, Lizard bite, Spider fighting, Bee sting, Spider
Collection: Animal Attacks, Parasitic Infestations, Stings, and Bites of the Skin, Spiders, Toxic Effects of Venomous Animals, Venomous Animals
Publisher: World Heritage Encyclopedia

Spider bite

Venomous spiders
Classification and external resources
ICD-10 T14.1 · T63.3
W57 (nonvenomous)
X21 (venomous)
ICD-9 989.5 · E905.1 · E906.4
DiseasesDB 12299
MedlinePlus 002858
eMedicine article/772484

Spider bite, sometimes called arachnidism in technical literature, is injury resulting from the bites of spiders. It is an unusual class of injury and the effects of most confirmed spider bites are trivial, even though nearly all species of spider are venomous. For all practical purposes arachnidism is substantial envenomation by a spider bite, their bites otherwise being medically insignificant. Depending on the species of spider and the victim, arachnidism will have various effects, ranging from going practically unnoticed, through transient pain, to gangrene, or fatal neurotoxicity.[1]:455 Brazilian wandering spiders of the genus Phoneutria are considered today to be the most dangerous spider species to humans, venom-wise.

Bites from the widow spiders (genus Latrodectus) produce a special class of arachnidism, a neurotoxic condition known as Latrodectism.[2]

Similarly, bites from the recluse spiders (genus Loxosceles) cause the condition called Loxoscelism, which has become particularly notorious in recent decades as the predominant cause of "necrotic arachnidism", in which necrosis of the surrounding tissue is the major concern.[3][4]

Another medical condition that has historically been claimed to arise from spider bites is Tarantism, but there is no substantial evidence for the existence of this supposed condition.


  • General considerations 1
  • Signs and symptoms 2
  • Pathophysiology 3
    • Neurotoxic venom 3.1
    • Necrotic venom 3.2
    • Comparative analysis 3.3
      • Measurements 3.3.1
  • Diagnosis 4
  • Management 5
    • Necrosis 5.1
    • Other 5.2
  • Epidemiology 6
    • Australia 6.1
    • United States 6.2
  • Classification 7
    • Brazilian wandering spiders 7.1
    • Australian funnel-web spiders 7.2
    • Tangle-web spiders 7.3
      • Widow spiders 7.3.1
      • False black widows 7.3.2
    • Sicariidae spiders 7.4
      • Six-eyed sand spiders 7.4.1
      • Recluse spiders 7.4.2
    • Mouse spiders 7.5
    • Tarantulas 7.6
      • New-world tarantulas 7.6.1
      • Old-world tarantulas 7.6.2
    • Yellow Sac spiders 7.7
    • Others 7.8
      • Hobo spiders 7.8.1
      • Lycosa tarantula 7.8.2
      • White-tailed spiders 7.8.3
      • Harvestman 7.8.4
      • Sun spiders 7.8.5
  • Historical remedies 8
  • See also 9
  • References 10
  • External links 11

General considerations

Spiders are predators and most species rely largely on their bites to subdue and kill their prey before consuming it. With the exception of web-building spiders that may feed on almost any creature that their webs can immobilise, spiders do not generally attack animals larger than themselves. However, some species also may bite in self-defense. Some in particular — e.g., Atrax robustus — will stand their ground when approached by larger animals, and will adopt an aggressive stance. Still, nearly all spider bites occur when humans unintentionally press up against spiders and receive a defensive bite.

Only two spider families,

  • Brazilian article reporting medical research
  • Medical Journal of Australia article gives statistics on the most frequent biters and the most serious bites.
  • Pictures and descriptions of spider bites from around the world.
  • Richard S. Vetter and P. Kirk Visscher of the University of California at Riverside
  • Spider bites are an overrated menace
  • How to Tell the Difference between MRSA and a Spider Bite
  • CDC - Venomous Spiders - NIOSH Workplace Safety and Health Topic

External links

  1. ^ James, William D.; Berger, Timothy G.; et al. (2006). Andrews' Diseases of the Skin: clinical Dermatology. Saunders Elsevier.  
  2. ^ Braitberg, George (2009). "spider bites: Assessment and management". Australian Family Physician 38 (11): 862–67. 
  3. ^ Vetter, Richard S. Myth: idiopathic wounds are often due to brown recluse or other spider bites throughout the United States. West J Med. Nov 2000; 173(5): 357–358. PMCID: PMC1071166
  4. ^ Isbister, GK. Necrotic arachnidism: the mythology of a modern plague. Lancet. 2004 Aug 7-13;364(9433):549-53
  5. ^ "Spider Bite First Aid". Retrieved 2007-08-23. 
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  7. ^ Vetter, R.S. (2008). "Spiders of the genus Loxosceles (Araneae, Sicariidae): a review of biological, medical and psychological aspects regarding envenomations". The Journal of Arachnology 36: 150–163.  
  8. ^ a b c Swanson D, Vetter R (2005). "Bites of brown recluse spiders and suspected necrotic arachnidism.". N Engl J Med 352 (7): 700–7.  
  9. ^ a b c d e "Global Family Doctor - Wonca Online | Item search". 
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  11. ^ Escoubas P (November 2006). "Molecular diversification in spider venoms: a web of combinatorial peptide libraries". Molecular Diversity 10 (4): 545–54.  
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  13. ^ Marcus V. Gomez, Evanguedes Kalapothakis, Cristina Guatimosim, 2 and Marco A. M. Prado. Venom: A Cocktail of Toxins That Affect Ion Channels"Phoneutria nigriventer". Cellular and Molecular Neurobiology 22 (5–6). 
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  15. ^ Binford GJ, Bodner MR, Cordes MH, Baldwin KL, Rynerson MR, Burns SN, Zobel-Thropp PA (March 2009). "Molecular Evolution, Functional Variation, and Proposed Nomenclature of the Gene Family That Includes Sphingomyelinase D in Sicariid Spider Venoms". Molecular Biology and Evolution 26 (3): 547–66.  
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  22. ^ Bennett, R. G. and R. S. Vetter. (2004). "An approach to spider bites: erroneous attribution of dermonecrotic lesions to brown recluse and hobo spider bites in Canada". Canadian Fam Physician 50: 1098–1101. 
  23. ^ James H. Diaz, MD (April 1, 2005). "Most necrotic ulcers are not spider bites". American Journal of Tropical Medicine and Hygiene 72 (4): 364–367. 
  24. ^ a b Isbister GK, Gray MR. "White-tail spider bite: a prospective study of 130 definite bites by Lampona species". Medical Journal of Australia 179 (4): 199–202. 
  25. ^ Isbister GK, Hirst D (August 2003). "A prospective study of definite bites by spiders of the family Sparassidae (huntsmen spiders) with identification to species level".  
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  27. ^ a b c d e f g h i j k l Vetter, Richard S. and Visscher, P. Kirk, Department of Entomology, University of California, Riverside, CA 92521 USA (July 1998). "Bites and Stings of medically important venomous arthropods". International Journal of Dermatology 37 (7): 481–496.  
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  29. ^ Occupational Health Southern Africa March April 2005
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  31. ^ While, Julian and Gray, Michael (1989). "Atrax Robustus". IPCS INCHEM. International Programme on Chemical Safety. 
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  33. ^ Sheumack DD, Baldo BA, Carroll PR, Hampson F, Howden ME, Skorulis A (1984). "A comparative study of properties and toxic constituents of funnel web spider (Atrax) venoms". Comparative biochemistry and physiology 78 (1): 55–68.  
  34. ^ Manson's tropical diseases By Gordon C. Cook, Patrick Manson, Alimuddin Zumla, p. 592
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  38. ^ a b (Tung Hai University, Taiwan, article in Chinese broken link)
  39. ^ a b c Ori, Masahisa and Ikeda, Hiroyoshi (1998). "Spider Venoms and Spider Toxins". Journal of Toxicology. 
  40. ^ a b c d M. F. Manzoli-Palma; N. Gobbi; M. S. Palma (2003). "Insects as biological models to assay spider and scorpion venom toxicity". Journal of Venomous Animals and Toxins including Tropical Diseases 9 (2): 174.  
  41. ^ a b c Barbaro KC, Ferreira ML, Cardoso DF, Eickstedt VR, Mota I (November 1996). "Identification and neutralization of biological activities in the venoms of Loxosceles spiders". Brazilian Journal of Med Biol Res 29 (11): 1491–7.  
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  43. ^ Lelle Petterson. "The genus Phoneutria, Perty 1833, wandering spiders". Minax tarantulas. 
  44. ^ Liang SP, Zhang DY, Pan X, Chen Q, Zhou PA (August 1993). "Properties and amino acid sequence of huwentoxin-I, a neurotoxin purified from the venom of the Chinese bird spider Selenocosmia huwena". Toxicon 31 (8): 969–78.  
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  48. ^ Peggy Peck (November 2004). "If the patient says spider bite, think MRSA, says Assembly speaker". American Academy of Family Physicians. Retrieved 2007-10-11. 
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See also

Recorded treatment from the 1890s for spider bites in general was rubbing in tobacco juice to the bitten skin,[87] similar to some of the traditional uses of the tobacco plant for various bites and stings from Central and South America.[88]

Historical remedies

Further, Solifugae are known to not possess any venom (other than one species in India, which may possess venom according to one study[85]). However, due to the large size of their jaws, bites by Solifugae can cause significant wounds, which should be treated accordingly to avoid infection.[86]

The arachnids of the order Solifugae, also known as wind scorpions or sun spiders, are neither spiders nor scorpions. In the Middle East, it is common belief among some American soldiers stationed there that Solifugae will feed on living human flesh. The story goes that the creature will inject some anesthetizing venom into the exposed skin of its sleeping victim, then feed voraciously, leaving the victim to awaken with a gaping wound. Solifugae, however, do not produce such an anesthetic, and do not attack prey larger than themselves unless threatened.

Sun spiders

The term "daddy-long-legs" also can refer to the similar-looking cellar spider. This species (a true spider) can bite humans, but its venom is not known to have any effects beyond mild discomfort at the site of the bite.

The spider-like arachnids known as Opiliones (also known as "harvestmen" or "daddy-long-legs"), are a species often handled by humans. They are the subject of an urban legend which not only claims that Harvestmen are venomous, but are in fact more venomous than any of the spiders but are incapable of biting humans due to their lack of penetration. This is untrue on several counts. None of the known species have venom glands or fangs, instead having chelicerae.[84] In addition, incidents of opiliones biting people are rare, and no reported bites by these species have had any lasting effects.

Opiliones (harvestman)


White-tailed spiders (Lampona spp.), indigenous to Australia and present as an invasive pest in New Zealand, have been blamed for a necrotic bite, producing symptoms similar to a brown recluse. However, a scientific study published in 2003 showed that their bites produce pain equivalent to a bee sting, a red mark, local swelling and itchiness; very occasionally nausea, vomiting, malaise or headache may occur. The study of 130 white-tailed spider bites found no necrotic ulcers or confirmed infections.[24]

White-tailed spiders

Lycosa tarantula, a species of wolf spider which is found near Taranto, Italy, Serbia, Montenegro (and the origin of the name tarantula, which today refers to a completely different kind of spider), was once blamed for a condition known as tarantism. Workers in the fields would suffer bites, and observe large, conspicuous, hairy spiders in the area. That spider, L. tarantula, was blamed for the pain and suffering (and occasional death) associated with tarantism. It is known that the bite of L. tarantula, while sometimes painful, has no serious medical consequences for humans. It is also suspected that the real culprit was another spider, Latrodectus tredecimguttatus, a type of widow spider, and one which is now known to be very dangerous to people. Lycosa Raptoria of South America has been reported (although still controversial) to have caused a painful bite followed by intense tissue swelling and in some cases either mild systemic effects or a necrotic lesion. It proves that, since so many spider bites are either unreported or misidentified, many of the large "vagrant" spiders such as Dolomedes, Lycosa, Ctenid (including the dangerous Phoneutria) and the Sparassids (Huntsman spiders) can all deliver bites of potential medical importance. In many cases, depending on a human beings age, immune system and sensitivity, a normally harmless spider bite to some humans can wreak havoc with others including anaphylactic shock, bacterial infections, sepsis, extreme swelling in the joints near the site of the bite, and necrotic lesions. In one case, a roof worker in New Hampshire was bitten by a large Dolomedes spider known as Dolomedes tenebrosus and within a few hours, his hand swelled up with radiating pain spreading up his arm plus dizziness and slight nausea. Later the bite wound produced a painful necrotic lesion that took weeks to heal and this was from a spider reportedly harmless. The question is, has this spider simply not been tested for its venom toxicity or was the victim allergic or hyper sensitive?

Lycosa tarantula. Its back is covered with recently hatched spiderlings.

Lycosa tarantula

However, in Europe, where the spider originates, the species is considered a harmless outdoor relative of the common house spider (Tegenaria domestica), and no other spider in the genus Tegenaria is considered to be harmful to people. Attempts to replicate Vest's study that reported necrotic effects of the venom have failed, thus casting the "dangerous" status of this spider into doubt. In addition, Vest's methodologies have been questioned; he has been accused of incorrectly attributing symptoms to hobo spider bites when no positive identification of the spider was made. The one fatality attributed to the spider by medical authorities has also been questioned, and there are no documented cases where an otherwise-healthy person has developed a necrotic lesion from a positively identified hobo spider bite. Many scientists now question whether or not the spider is harmful at all.[82][83]

The hobo spider, Tegenaria agrestis, may wander away from its web, especially in the fall, and thus come into contact with people and potentially bite. This spider is found in the northwestern United States, western Canada and throughout much of Europe. Studies performed by arachnologist Darwin Vest reported that this spider's venom caused significant necrotic effects in laboratory animals,[80][81] and medical authorities in the Pacific Northwest who were aware of Vest's research subsequently blamed this spider for at least one fatality. Many agricultural authorities have published the advice that this species is potentially harmful, and medical personnel in the western United States and Canada have been advised to consider hobo spider bites when patients present with necrotic wounds. Many brown recluse bites have been reported in the U.S. west coast states (Washington, Oregon, and northern California) where populations of brown recluse spiders have not been found; some of these alleged bites have been attributed to hobo spiders instead.[47]

Male Hobo Spider - note the large pedipalps

Hobo spiders

There are several species of spider (and a few other arachnids which are not spiders, but are frequently confused with them), who have had unsupported reputations for being harmful to humans. In some cases, that the species is now considered harmless is a settled matter for arachnologists and other professionals; in other cases (such as the hobo spider), prior scientific belief that a spider is harmful to humans is now being questioned.


The Yellow Sac spiders, Cheiracanthium sp., take shelter in silk tubes during the daytime and generally come out to hunt at night. These pale yellow or whitish spiders are often found in houses at the top of walls, or wandering across ceilings. They are also commonly found outdoors on foliage. The draglines they leave while hunting are one of the most common "spiderwebs" that are removed with broom and vacuum cleaner. People may unintentionally make contact with them in the dark and so be bitten if the spider is irritated or provoked. However, many people will live their entire lives in close proximity to them and never suffer a bite. Nevertheless, the spider's bite is considered toxic.

Yellow Sac spider Cheiracanthium punctorium

Yellow Sac spiders

One tarantula whose venom has been studied extensively is the Chinese bird spider, a tarantula of the subfamily Ornithoctoninae. The venom has been found to contain numerous novel toxins, is effective at killing mice, and has been blamed for at least one fatality in China. However, there is little documented clinical evidence of the effects of this spiders' bite in humans, so firm conclusions about the level of danger posed by this spider cannot be drawn.

There have been reports of significant bites by Poecilotheria species, occasionally resulting in hospitalization. Symptoms include localized pain and swelling, exhaustion, moderate to severe muscle cramping, labored breathing and fever, sometimes delayed days after the initial bite.[76][77][78][79]

Old-world tarantulas, especially those indigenous to Asia, lack urticating hairs and use biting as a defensive mechanism as well for subduing prey. They are far less docile than new-world tarantulas, and are more likely to bite when provoked. Incomplete studies of old-world tarantula venoms, as well as anecdotal evidence, suggests that they are more potent than those of new-world counterparts.

Cobalt blue tarantula (Haplopelma lividum), an old-world species

Old-world tarantulas

New-world tarantulas—those indigenous to the Americas—have bites that generally pose little threat to humans (other than causing localized pain). The primary defense deployed by these spiders is by means of urticating hairs, which can cause irritant symptoms in humans.

Mexican Red Knee tarantula (Brachypelma sp.), a new-world species

New-world tarantulas

The tarantulas of the family Theraphosidae are fearsome-looking spiders with (sometimes justified) reputations for inflicting harm. As large spiders, they have very powerful fangs and are capable of delivering a sizable quantity of venom. However, many tarantula species are known to be relatively harmless to humans.


The mouse spiders of the genus Missulena are a type of primitive burrowing spider found primarily in Australia. Several species of this genus are known to possess a venom which contains compounds similar to atracotoxin, the substance in funnel-web venom which is deadly to humans, and there have been several recorded bites by this spider producing severe symptoms requiring emergency medical treatment. However, unlike the funnel-web spiders, which have resulted in at least 13 deaths in the last 100 years,[36] there are no recorded human fatalities due to mouse spider bites, and many bites by this spider result in no serious complications. It is suspected that unlike Atrax and Hadronyche, which typically deliver full envenomations when they bite, that mouse spiders often give "dry" bites. When severe envenomation does occur, funnel-web antivenom has been shown to be effective.[75]

Mouse spiders

Even more dangerous is the Chilean recluse, a species native to South America and found in many parts of the world, including in southern California and other southwestern states. Bites of this spider have been known to cause systemic reactions in 15% of reported cases, and fatalities in 3-4% of cases.[74]

Serious systemic effects may occur before this time, as the venom spreads throughout the body in minutes. Mild symptoms include nausea, vomiting, fever, rashes, and muscle and joint pain. Rarely more severe symptoms occur including hemolysis, thrombocytopenia, and disseminated intravascular coagulation.[21] Debilitated patients, the elderly, and children may be more susceptible to systemic loxoscelism. Deaths have been reported for both the brown recluse and the related South American species L. laeta and L. intermedia.

A minority of bites form a necrotizing ulcer that destroys soft tissue and may take months and, on very rare occasions, years to heal, leaving deep scars similar to MRSA. The damaged tissue will become gangrenous and eventually slough away. The initial bite frequently cannot be felt and there may be no pain, but over time the wound may grow to as large as 10 inches (25 cm) in extreme cases. Bites usually become painful and itchy within 2 to 8 hours, pain and other local effects worsen 12 to 36 hours after the bite with the necrosis developing over the next few days.[20]

Most recluse spider bites are minor with little or no necrosis. However, a small number of bites produce severe dermonecrotic lesions, and, sometimes, severe systemic symptoms, including organ damage. Rarely the bite may also produce the systemic condition with occasional fatalities.

Recluse spiders (Loxosceles spp.), such as the brown recluse spider, also known as "violin spiders," "fiddlers," or "fiddlebacks," from the dark violin-shaped marking on the cephalothorax, are slow-moving, retiring spiders which wander about in dim areas and under things, and so are more easily trapped against one's skin by clothing, bed sheets, etc. The spiders will often creep along at a very slow pace and then make a sudden dart for a couple of inches, then return to the previous languid pace. Recluses are extremely venomous. Most encounters with this spider occur from moving boxes or rooting about in closets or under beds. The range of the brown recluse, L. reclusa in the US is approximately the southern two-thirds by the eastern three-quarters of the country. A number of related recluse spiders (some non-native introductions) are found in southern California and nearby areas.[72][73]

Recluse spiders

The six-eyed sand spider, of southern Africa and others of the genus Sicarius inject a cytotoxic venom, believed to contain sphingomyelinase D,[71] for which there is currently no antivenom. Fortunately, this specimen rarely interacts with humans, and is seldom known to bite. This spider buries itself in sand in order to ambush prey that wanders nearby. Sand particles adhere to cuticles on its abdomen, thus acting as a natural camouflage if uncovered. If disturbed, it will run a short distance and bury itself again.

Six-eyed sand spiders

The family Sicariidae includes two genera which inflict necrotoxic bites. One genus, Loxosceles, comprises the recluse spiders (below). The other genus, Sicarius is found only in the southern hemisphere, an example being the Six-eyed sand spider, Sicarius hahni

Sicariidae spiders

Members of this genus are characterized by the "D" shape of the cephalothorax, and the way the relatively straight line thus formed is mirrored by the blunt forward surface of the abdomen. Other genera in this family generally have cephalothoraxes that are more oval in shape or even rather round, and that give the appearance of two body parts that are joined by a small connector.

Use of widow spider antivenom has been shown effective in treating steatodism.[70] The genera Steatoda and Latrodectus are biologically close cousins; both belong to the family Theridiidae. There are over 100 species in this genus, but only several species have been associated with medically significant bites.

The False black widow spiders (also known as false katipo, false button spider, cupboard spider, and in Australia, brown house spider) are spiders of the genus Steatoda. They resemble widow spiders in size and physical form, due to being members of the same family. While the bite of Steatoda spiders is nowhere near as serious as that of true widow spiders, several of these spiders do have medically significant bites. The bite of Steatoda grossa, commonly known as the cupboard spider, is known to cause symptoms which have been described as a very minor widow bite; the medical community now refers to the symptoms of Steatoda bites as steatodism. Other spiders in this genus known to be problem biters include two chiefly European varieties, S. paykulliana and S. nobilis, and a species found mainly in New Zealand and South Africa, S. capensis

False black widows

The venom, while seldom life-threatening, produces very painful effects including muscle spasms, 'tetanus-like' contractions and, in some cases, spinal or cerebral paralysis (which is generally temporary, but might leave permanent damage to central nervous system). A serious bite will often require a short hospital stay. Children, elderly, and ill individuals are at most risk of serious effects.

Like many spiders, widows have very poor vision, and they move with difficulty when not on their web. Widow spiders are large, strong-looking house spiders (but still have relatively spindly legs and deep, globular abdomens). The abdomen is dark and shiny, and has one or several red spots, either above or below. The spots may take the form of an hourglass, or two triangles, point-to-point. Male widows, like most spider species, are much smaller than the females and may have a variety of streaks and spots on a browner, less globular abdomen. The males are generally less dangerous than the females of the same species. Widows tend to be non-aggressive, but will bite if the web is disturbed and the spider feels threatened.

The widow spiders (genus Latrodectus), such as the black widow, redback spider, and katipo are spiders that carry a neurotoxic venom[69] which can cause a set of symptoms known as Latrodectism.

Latrodectus hasselti, the Redback spider

Widow spiders

Two genera of the tangle web spiders have venom which is known to be medically significant. One genus, the widow spiders of genus Latrodectus, has caused more human fatalities than any other. The other genus, the false widow spiders of Steatoda, has a far less serious bite.

Tangle-web spiders

One other genus in the Hexathelidae family has been reported to cause severe symptoms in humans. Severe bites have been attributed to members of the genus Macrothele in Taiwan, but no fatalities.[46]

A. robustus is one of three designated species of the genus Atrax.[66][67] The related genus Hadronyche is represented by about 40 other dangerous species in eastern Australia, including Queensland and Tasmania. The males in this case have somewhat more potent venom than females and they also wander, making them more likely to be encountered in summer. Bites by males of two large species, the Sydney funnel-web and northern tree funnel-web, have resulted in death.[68]

Range of the two genera (Hadronyche and Atrax) of venomous Australian funnel-web spiders

The Australian funnel-web spiders, such as the Sydney funnel-web spider Atrax robustus (a mygalomorph only distantly related to the araneomorph funnel-web spiders) are regarded as among the most dangerous in the world. They react vigorously to threats and, reputedly, will more often attempt to bite than run away. A. robustus, a large black spider, is found within a radius of about 100 km from Sydney. Its venom contains a compound known as atracotoxin which is highly toxic to primates. Unlike the Brazilian wandering spider, which is alleged to occasionally deliver dry bites, these spiders typically deliver a full envenomation when they bite.[64][65]

Threat display by a Sydney funnel-web spider (Atrax robustus).

Australian funnel-web spiders

Children are more sensitive to the bites of wandering spiders, as the spiders often make threat gestures (such as raising up their legs, or hopping sideways on the ground), which might amuse a child to the point of reaching towards the spider.[61] In male humans, bites of this spider may also result in priapism.[62] Scientists are attempting to create an erectile dysfunction treatment that can be combined with other medicines out of the peptide that causes this reaction.[63]

As their name suggests, Brazilian wandering spiders are active hunters and travel a lot. They tend to crawl into cozy, comfortable places for the night, and thus can easily be found in fruits and flowers that humans consume and cultivate. If the spider has a reason to be alarmed, it will bite in order to protect itself, but unless startled or provoked, most bites will be delivered dry (without venom). Venom bites will occur if the spider is pressed against something (such as fingers) and hurt. In this case, the high levels of serotonin contained in the venom, plus at minimum strong chelicera, will contribute to deliver a very painful bite that can result in muscle shock.

The Brazilian wandering spider (a ctenid spider) is a large brown spider similar to North American wolf spiders in appearance, although somewhat larger. It has a highly toxic venom (the most neurologically active of all spiders), and is regarded (along with the Australian funnel-web spiders, whose bites deliver slightly less venom, but are faster-acting) as among the most dangerous spiders in the world.[60] Based on one of the few pharmacological studies performed in the 1970s, Phoneutria's venom toxicity was more virulent than both Atrax and Latrodectus. The amount of P. nigriventer venom necessary to kill a 20 g mouse has been shown to be only 6 μg intravenously and 134 μg subcutaneously as compared to 110 μg and 200 μg respectively for Latrodectus mactans (Southern black widow). This ranks Phoneutria venom among the most deadly spider venoms to mice. Laboratory mice subjected to P. nigriventer venom experienced intense penile erections before succumbing to the toxin (from a table measuring the pharmacological toxicity of spiders Venomous Animals and their Venoms, vol. III, ed. Wolfgang Bücherl and Eleanor Buckley)

Brazilian wandering spider (Phoneutria nigriventer).

Brazilian wandering spiders

The following types of spider are known to have medically significant bites, with symptoms ranging from localized pain all the way to severe tissue destruction and potential death. Spiders whose bites have caused fatalities which are well documented in the scientific literature are so indicated in the section headers. Only four genera (Phoneutria, Atrax, Latrodectus, and Loxosceles) are known to have killed humans; three other genera (Hadronyche, Missulena, and Sicarius) possess venom which toxicology studies have shown have lethal potential (being similar to Atrax and Loxosceles venom in composition). There are suspected but unconfirmed deaths reported in the literature from species in Tegenaria and Haplopelma.

A spider is classified as "venomous" if it is able to cause significant harm to humans.[9] Spiders having medically significant venom exist in all but the coldest parts of the world. There is general agreement on which spiders give bites that may produce lasting damage or death, but not such general agreement on how one might sort spiders identified by genus and species in order of their threat to humans.


[59] Black widow spider bites may cause muscle cramps, but no one in the United States has died from a black widow spider bite in over 10 years.[58] The spiders of most concern in the United States and North America are

United States

A study of 750 definite spider bites in Australia indicated that 6% of spider bites cause significant effects, the vast majority of these being redback spider bites causing significant pain lasting more than 24 hours.[57]



  • Studies have shown surgical intervention is ineffective and may worsen outcome. Excision may delay wound healing, cause abscesses, and lead to objectionable scarring.[54]
  • Use of antivenom for severe spider bites may be indicated, especially in the case of neurotoxic venoms.[55] Effective antivenoms exist for Latrodectus, Atrax, and Phoneutria venom. Recluse bites are treatable by antivenom; an antivenom for Loxosceles bites is available in South America, and it appears antivenom may be the most promising therapy. However, the recluse antivenom is most effective if given early, and because of the relatively painless bite delivered by recluses, patients do not often present until 24 or more hours after the event, possibly limiting the effect of this intervention.[56] Due to the risk of serum sickness, use of antivenom is generally not indicated unless serious symptoms are present, and/or a person fails to respond to other forms of treatment.


Dapsone is commonly used in the USA and Brazil for the treatment of necrosis. There have been conflicting reports about its efficacy and some have suggested it should no longer be used routinely, if at all.[53]

There is no established treatment for necrosis. Recommendations include elevation and immobilization of the affected limb, application of ice, local wound care, and tetanus prophylaxis. Many other therapies have been used with varying degrees of success including hyperbaric oxygen, dapsone, antihistamines (e.g., cyproheptadine), antibiotics, dextran, glucocorticoids, vasodilators, heparin, nitroglycerin, electric shock, curettage, surgical excision, and antivenom. None of these treatments have been subjected to controlled, randomized trials to conclusively show benefit. In almost all cases, bites are self-limited and typically heal without any medical intervention.[8]


Treatment for non-poisonous spider bites include washing the bite with soap and water and ice to reduce inflammation.[9] Analgesics and antihistamines may be used, however antibiotics are not recommended unless there is also a bacterial infection present.[9]

In the case of bites by widow spiders, Australian venomous funnel-web spiders, or Brazilian wandering spiders, prompt medical attention should be sought as in some cases the bites of these spiders may develop into a medical emergency.[51][52]

Most spider bites are harmless, and require no specific treatment. Treatment of bites may depend on the type of spider; thus, capture of the spider—either alive, or in a well-preserved condition, is useful.[49][50]


Occasionally, infections of methicillin-resistant Staphylococcus aureus (MRSA) are misdiagnosed as necrotic spider bites; this can have severe consequences as a MRSA infection is frequently a medical emergency.[48]

Assumption that a reported injury was caused by a spider is the most common source of false reports, which in some cases have led to misdiagnosis and mistreatment, with potentially life-threatening consequences.[47] Many spider bites, including those by some dangerous species, are relatively painless at first and may go unnoticed if not directly observed. These bites may only be noticed later if serious symptoms appear.


* This value is based on experience with human exposures.
** Several other kinds of tarantulas in the pet trade are regarded as giving non-trivial bites. Tarantulas are typically far larger than spiders with the most toxic kinds of venom. However, the sheer volume of the venom may compensate for its lesser toxicity. The effects of a full envenomation are probably unknown for many species of tarantulas, so due caution is advisable.

Genus Species Common name Body length Venom amount LD-50 Alternate LD-50 Deaths reported
Atrax A. robustus Sydney funnel-web spider 24–32 mm.[27] 0.25 mg (F) and 0.81 mg (M) [31] 2 mg [32] 0.16 mg/kg [33] unknown 13 attributed deaths from 1927 to 1980[34]
Hadronyche H. formidabilis Northern tree funnel-web spider 23–45 mm. 1 death.[35] High rates of severe envenoming.[27][36]
Hadronyche H. cerberea Southern tree funnel-web spider High rates of severe envenoming.[36]
Latrodectus L. mactans Black widow 8–15 mm [27] 0.02–.03 mg.[37][38] 0.002 mg/kg [37]* 0.9 mg/kg 36 deaths recorded from 1965 to 1990 in the U.S.
5% of reported bites prior to antivenom availability [27]
Latrodectus L. tredecimguttatus Malmignatte (approx. same) (approx. same) 0.68 μg/kg [39] 16.25 μg/kg [39] possibility of deaths in Southern Europe first attributed to the brown recluse, suggesting larger frequency of the bites.
Loxosceles L. reclusa Brown recluse 1.2 cm (0.75 in) [27] 6–10 mm [27] .13–.27 mg.[39][40] necrosis and amputation of limbs more common, deaths rare[27]
Loxosceles L. intermedia 0.48 mg/kg [41]
Loxosceles L. laeta Chilean recluse 1.45 mg/kg [41]
Loxosceles L. gaucho 0.74 mg/kg [41]
Phoneutria P. bahiensis Brazilian wandering spider 30 mm 1.079 mg [42] .00061–.00157 mg/kg [42] cardiac failure reported in 5 out of 12 bitten
Phoneutria P. boliviensis Brazilian wandering spider 30 mm 1.079 mg.[42] .00061–.00157 mg/kg [42]
Phoneutria P. fera Brazilian wandering spider 30 mm [27] 1.079 mg [42] .00061–.00157 mg/kg [42] disputed effectiveness of the antivenin - 4 deaths out of 7 administered [27]
Phoneutria P. nigriventer Brazilian wandering spider 3–5 cm (1.25–2 in) [43] 2.15 mg [40] 1.079 mg.[42] 15.20 ng/mg.[40] 00061–.00157 mg/kg [42] 200 µg/kg (0.2 ng/mg) [40] severe cardiac failure, signs of priapism and irreversible damage to the central nervous system recorded.
18 deaths in Brazil alone from 2007 to 2010 [27]
Phoneutria P. reidyi Brazilian wandering spider 30 mm .00061–.00157 mg/kg [42] 0.3 mg/kg
Sicarius spp. Six-eyed sand spider 17 mm large necrotic lesions
Haplopelma H. huwenum (previously Selenocosmia huwena) Chinese bird spider 0.70 mg/kg [44] 1 death reported of a 5-year-old child suffocated, possibly caused by allergens to the venom.
Poecilotheria P. ornata Fringed ornamental tarantula Instances of coma reported.[45]
Poecilotheria P. fasciata ** Sri Lankan ornamental tarantula Instances of cardiac failure reported [45]
Cheiracanthium spp. Yellow Sac spider 6–10 mm one case of irreversible damage to the skin reported [27]
Cheiracanthium C. japonicum Japanese sac spider 6–10 mm
Macrothele M. holsti, M. gigas, M. taiwanensis [38] Primitive burrowing spiders No deaths reported in Taiwan.[46]
Steatoda S. grossa Cupboard spider Mild widow-like symptoms reported, no severe consequences
Study suggests its venom can be effective in treating widow bites because of their similarity.

Most LD-50 figures are based on experiments with laboratory mice. There are great differences in the sensitivities of various kinds of organisms to various kinds of venom. The relative sensitivities of mice to various venoms may not allow prediction of the exact degree of human sensitivity. So most of these figures can only give a rough approximation of the medical consequences of various spider bites to humans. A case in point are the Sicarius spp. The venom of these spiders is extremely active in laboratory animals, but there are few if any documented reports of Sicarius bites in humans, so data on which to base valid conclusions is lacking.

The LD-50 (median lethal dose) figures have limited utility since the effects of venoms differ widely from species to species. Before an antivenom was developed, deaths from Atrax and Hadronyche did occur, but the frequency of non-lethal bites is unknown. Some deaths from Phoneutria bites are reported, but much of their range is in the Amazon so reporting of bites may not be very complete.


The genus Latrodectus (of which the black widow spider is the most notorious) have been credited with killing more people per year, worldwide, than any other spider. Because they are not very large, they are much harder to detect than a large Brazilian wandering spider or a tarantula. Their venom is extremely potent. Compared to many other species of spiders, their chelicerae are not very large. In the case of a mature female, the hollow, needle shaped part of each chelicera, the part that penetrates the skin, is approximately 1 mm (0.04 in) long, sufficiently long to inject the venom to a dangerous depth. The males, being much smaller, can inject far less venom and inject it far less deeply. The actual amount injected, even by a mature female, is very small in physical volume (.02–.03 mg). On the other hand, the geographical range of the widow spiders is very great. As a result, far more people are exposed, worldwide, to widow bites than are exposed to bites of more dangerous spiders. Widow spiders venom may rarely cause serious complications in people. Fatalities had been reported as high as 5% of bites and as low as 0.2% of bites.[30]

The spider-bites documented as the most dangerous to humans are those of the Sydney funnel-web spider and the Brazilian wandering spider. These spiders are potentially more dangerous than widow spiders because they have longer fangs and can inject greater quantities of venom to greater depths. Phoneutria nigriventer has approximately 2 mg of venom, but frequently gives dry bites or at least does not deliver all of its available venom. Only 1 out of 200 bites is serious [28]Atrax robustus has approximately 1.7 mg of venom. Bites of Six-eyed sand spiders have been described as dangerous to humans, but there is a lack of proof for this.[29]:p.25

It should also be noted that serious bites develop symptoms quickly, within the hour. While a serious medical condition may result (see latrodectims and loxocelism) fatalities are exceedingly rare. Appropriate medical treatment can improve speed of recovery . The scenario given in movies such as Arachnophobia, where bite victims die within minutes, does not occur. Small children are considered an exception because the amount of venom dispersed throughout the body is many times the concentration in an adult. There is at least one recorded case of a small child dying within 15 minutes of a bite from a Sydney funnel-web spider; that death occurred before the development of an antivenom. Since the antivenom was developed there have been no fatalities due to this species.

  • Firstly, it is often the case that a spider bite is "dry" – the skin may be pierced, but little or no venom is injected into the victim. In such an instance, little or none of the spider's dangerous potential for harm is manifested.
  • Secondly, there have been reports of allergic reactions to spider contact but only one of anaphylactic shock,[26] a life-threatening condition (much the same as a sting from an ant, bee, or wasp may produce a harmful effect apart from the toxic quality of its venom).[27]
  • Thirdly, many spiders listed as dangerous are seldom encountered, or have dispositions that make them unlikely to bite despite the high toxicity of their venom.
  • Finally, little is known about the toxicity of many spiders, due to their infrequent encounters with humans; the list of venomous spiders is limited to those that are linked to medical events in humans or who otherwise have been extensively studied.

It is often asked which type of spider is the most "dangerous" in the world. There isn't a simple answer to this question, as there are many things which must be taken into account when considering the amount of danger posed by spider bites:

Comparative analysis

Numerous other spiders have been associated with necrotic bites. Examples include the Hobo spider, a member of the usually inoffensive family Agelenidae and various Sac spiders, members of the family Miturgidae. However, the bites from these spiders do not conclusively cause skin necrosis and none are known to produce the severe symptoms that rarely follow from a recluse spider bite.[22][23] So far, no known necrotoxins have been isolated from the venom of any of these spiders, and some arachnologists have disputed the accuracy of many spider identifications carried out by bite victims, family members, medical responders, and other non-experts in arachnology. There have been several studies questioning whether danger is posed by some of these spiders. In these studies, scientists examined case studies of bites in which the spider in question was positively identified by an expert, and found that the incidence of necrotic injury diminished significantly when "questionable" identifications were excluded from the sample set.[24][25]

Systemic effects are unusual but include Mild symptoms such nausea, vomiting, fever, rashes, and muscle and joint pain. Rarely, more severe symptoms occur including red blood cell destruction (hemolysis), low platelets (thrombocytopenia), and loss of clotting factors (disseminated intravascular coagulation).[21] Children may be more susceptible to systemic loxoscelism effects. Deaths have been reported for both the brown recluse and the related South American species Loxosceles laeta and Loxosceles intermedia related to hemolysis and the injury that results to the kidney. However, some deaths have occurred where no brown recluse live leading to perception of misdiagnosis.

Spiders known to have necrotic venom occur most notoriously in the family Sicariidae, which includes both the recluse spiders and the six-eyed sand spiders. Spiders in this family possess a known dermonecrotic agent sphingomyelinase D,[14][15] which is otherwise found only in a few pathogenic bacteria.[16][17] Some species in this family are more venomous than others; according to one study, the venom of the Chilean recluse and several species of six-eyed sand spider indigenous to southern Africa, contains an order of magnitude more of this substance than do other sicariid spiders such as the brown recluse.[18] Bites by spiders in this family can produce symptoms ranging from minor localized effects, to severe dermonecrotic lesions, up to and including severe systemic reactions including renal failure, and in some cases, death.[19] Even in the absence of systemic effects, serious bites from sicariid spiders may form a necrotising ulcer that destroys soft tissue and may take months and very rarely years to heal, leaving deep scars. The damaged tissue may become gangrenous and eventually slough away. Initially there may be no pain from a bite, but over time the wound may grow to 10 inches (25 cm) in extreme cases. Bites usually become painful and itchy within two to eight hours, pain and other local effects worsen 12 to 36 hours after the bite, and then necrosis will develop over the next few days.[20]

Necrotic venom

The majority of spiders with serious bites possess a neurotoxic venom of some sort, though the specific manner in which the nervous system is attacked varies from spider to spider.[10][11][12]

Neurotoxic venom

Spider venoms work on one of two fundamental principles; they are either neurotoxic (attacking the nervous system) or necrotic (attacking tissues surrounding the bite, and, in some cases, attacking vital organs and systems).

All spiders are capable of producing venom, with the exception of the hackled orb-weavers, the Holarchaeidae, and the primitive Mesothelae. (Other arachnids often confused with spiders, such as the harvestman and sun spiders, also do not produce venom). Nonetheless, only a small percentage of species have bites that pose a danger to people. Many spiders do not have mouthparts capable of penetrating human skin. While venoms are by definition toxic substances, most spiders do not have venom that is sufficiently toxic (in the quantities delivered) to require medical attention and, of those that do, fatalities are exceedingly rare. (For details that substantiate these claims, see the remainder of this article.)

A primary concern of the bite of a spider is the effect of its venom. A spider envenomation occurs whenever a spider injects venom into the skin. Not all spider bites involve injection of venom into the skin, and the amount of venom injected can vary based on the type of spider and the circumstances of the encounter. The mechanical injury from a spider bite is not a serious concern for humans. Some spider bites do leave a large enough wound that infection may be a concern. However, it is generally the toxicity of spider venom that poses the most risk to human beings; several spiders are known to have venom that can cause injury to humans in the amounts that a spider will typically inject when biting.


Pain from non-venomous spider bites typically lasts for 5 to 60 minutes while pain from venomous spider bites frequently lasts for longer than 24 hours.[9] The rate of a bacterial infection due to a spider bite is low (0.9%).[9]

4 months after a brown recluse spider bite with scar remaining
A Brazilian man 31 hours after having been bitten on his face by a Loxosceles spider.

Signs and symptoms

Spider bites commonly are misdiagnosed by both the general public and medical practitioners. Many other conditions, both infectious and non-infectious can be confused with spider bites.[7] Many of these conditions are far more common and more likely to be the source of necrotic wounds.[8]

In various combinations and concentrations, medically significant spider venoms include necrotic agents, neurotoxins, and pharmacologically active compounds such as serotonin. Out of over 40,000 known species of spider only some two hundred species in twenty genera are known to have medically significant bites, a few of them potentially lethal.[6] In most cases of bites, the chief concern is the spider's venom, although in some cases medically non-significant spiders can transmit infectious diseases or serious non-contagious infections.


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