Spider bite
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Aesopos
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<nowiki></nowiki>{{Infobox_Disease |
Name = Spider bite |
Image = |
Caption = |
DiseasesDB = 12299 |
ICD10 = {{ICD10|T|63|3|t|51}} |
ICD9 = {{ICD9|989.5}} |
ICDO = |
OMIM = |
MedlinePlus = |
eMedicineSubj = |
eMedicineTopic = |
}}
[[Image:Black Wishbone.jpg|right|thumb|[[Chelicerae]] of a [[Aname atra|black wishbone]] (Nemesiidae) spider, a [[mygalomorphae|mygalomorph]]]]
[[spider|'''Spiders''']] occasionally bite humans. Although 98-99% of spider bites are harmless,<ref>{{cite web | last = | first = | title =Spider Bite First Aid | publisher = firstaidkits.org | date = | url =http://www.firstaidkits.org/spider-bites.asp | accessdate = 2007-08-23}}</ref> more rarely, the symptoms of their bites can include [[Necrosis|necrotic]] wounds, systemic toxicity, and in some cases, death. Four [[genus|genera]] are known to have potentially lethal bites.<ref name="Global">
{{cite journal|
author=Diaz, James H|
title=The global epidemiology, syndromic classification, management, and prevention of spider bites|
journal=American Journal of Tropical Medicine and Hygiene|
volume=71|
issue=2|
date=2004|
url=http://www.ajtmh.org/cgi/content/full/71/2/239|
pages=239–250|
pmid=15306718}}</ref>
In almost all cases of spider bite, the chief concern is the spider's [[venom]]. Spiders regarded as dangerous possess venom which is toxic to humans in the quantities which can be delivered by a single bite of a single spider at one time.
Experts on spider bites have noted that misdiagnoses of bites by both the general public and the medical community are quite common; many other conditions and diseases are confused with spider bites, sometimes preventing or delaying proper remedy, which can lead to deleterious outcome<ref>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</ref>. For example, there are numerous documented infectious and noninfectious conditions (including [[pyoderma gangrenosum]], bacterial infections by ''[[Staphylococcus]]'' (including [[MRSA]]) and ''[[Streptococcus]]'', [[herpes]], diabetic ulcer, fungal infections, chemical burns, [[toxicodendron]] dermatitis, [[squamous cell carcinoma]], localized [[vasculitis]], [[syphilis]], [[toxic epidermal necrolysis]], [[sporotrichosis]], and [[Lyme disease]]) that produce wounds that have been initially misdiagnosed as [[brown recluse]] spider bites by medical professionals; many of these conditions are far more common and more likely to be the source of mysterious necrotic wounds, even in areas where recluses actually occur<ref name="NEJM2005-Vetter">{{cite journal | author = Swanson D, Vetter R | title = Bites of brown recluse spiders and suspected necrotic arachnidism. | journal = N Engl J Med | volume = 352 | issue = 7 | pages = 700-7 | year = 2005 | id = PMID 15716564 | doi = 10.1056/NEJMra041184 | doi = 10.1056/NEJMra041184}}</ref>.
The use of the terms "poison" or "poisonous" in the context of spider bites is discouraged, as [[poison]] generally refers to substances which are harmful if absorbed through epithelial linings (e.g., eaten, or absorbed through the skin). The effect of eating spiders is, in general, unknown, but some spiders (such as [[tarantula]]s) are sometimes consumed as food.<ref>{{cite news|author=Rigby, Rhymer|title=Tuck in to a tarantula|publisher=Sunday Telegraph|date=2003-09-23|url=http://www.rhymer.net/cutsE.htm}}</ref>
== Biology and ecology of spider bites ==
[[Image:Phidippus audax3.JPG|thumb|right|Exposed chelicerae of ''[[Phidippus audax]]'']]
Spiders are [[predator]]y animals that consume other animals (including other spiders) for food. For the vast majority of spider species, biting (and injection of venom) is the way the spiders subdue their prey; the spiders will use their venom to [[paralysis|paralyze]] or kill their victims, often consuming them later. Spiders also use biting as a defensive mechanism, though the primary purpose of spider venom is to capture food.
===Spider mouthparts===
[[Image:Cheiracanthium punctorium frei 1 17 Forst Jungfernhdeide Jg 46 070920.jpg|Threatening ''[[Cheiracanthium punctorium]]''|thumb|250px|left]]
[[Image:Spider chelicerae.png|thumb|left|250px|
This overhead drawing shows the chelicerae in black, the surface of the cephalothorax in brown, the legs in reddish brown, and the venom glands and surrounding muscle tissue in green. The fang portion of the right chelicera can be seen projecting into the space between the two chelicerae.]]
[[Image:Psalmopoeus cambridgei Fang 60x.jpg|thumb|right|The fang of this immature ''Psalmopoeus cambridgei'' spider is about 2mm long. The spider herself is about 25mm long]]
Spiders do not have teeth. Instead, they have two [[chelicerae]], each with two segments, the ''fang'' and the basal portion. The fang, the organic functional equivalent to a [[hypodermic needle]], is what penetrates the skin, fur, or exoskeleton of the spider's target — spider mouthparts are primarily intended for envenoming a spider's prey in most species, typically [[insect]]s and other small [[arthropod]]s; not for biting humans. The basal portion includes all or part of the spider's venom glands, which can be squeezed under voluntary control by the spider to force venom out of the glands and into the wound.<ref name="Foelix">
{{cite book|
author=Foelix, Rainer F.|
title=Biology of Spiders (2nd edition)|
publisher=Oxford University Press|
isbn= ISBN 0-19-509594-4|
date=1996}}</ref>
The images in this section show the fang of an immature ''[[Psalmopoeus cambridgei]]'' at various levels of magnification, with various commercially available needles shown for comparison.
When a spider bites, the two parts of each ''chelicera'' come together like a folding knife, and when making a threat display or actually preparing to bite, the spider will also open the angle of the fangs with the basal portion of ''chelicerae'' and also open the angle of the basal portion with the cephalothorax. In the tarantulas and other [[Mygalomorphae]], the horizontal separation of the tips of the fangs does not change much, but in the other spiders the tips of the fangs move apart from each other as well as elevating. In more precise, scientific terms, the bite mechanism is called either "co-axial" or "bi-axial". The Mygalomorphea (Tarantulas, Trapdoor spiders etc.) offer a co-axial bite while the Labidognatha sub order, comprising all other spiders such as Lycosids, Ctenids and most web spiders, etc. deliver the more common bi-axial bite.
Even the tips of the fangs of the rather large spider shown above are quite sharp, and the spider's body is well adapted to driving the fangs into flesh. Some spider bites, such as those of the [[Sydney funnel-web spider]], are reported to have penetrated toe nails and soft leather shoes.
[[Image:Psalmopoeus cambridgei Fang & sewing needle.jpg|thumb|left|10x microphotograph of the ''chelicera'' and the tip of the smallest sewing needle available in ordinary commerce]]
===Types of bites===
Spiders have the capability to control how much venom (if any) is injected into a target, and adjust the dosage given according to circumstances. As venom costs the spider energy to produce, it is advantageous to the spider not to waste it. Spider bites are characterized as either '''attacking''' or '''defensive''', depending on whether the spider is attempting to subdue prey, or to repel a perceived threat. When capturing prey, spiders will typically adjust the amount of venom delivered based on the size of the meal; when defending itself, a spider's only goal is to secure relief from being squeezed or otherwise injured. A bite in which little or no venom is injected is frequently referred to as a '''dry bite'''.
As spiders do not [[predator|prey]] on humans (or other large mammals), spiders do not "attack" people. It is rare for spiders to mistake humans for prey.
Almost all bites that humans receive are defensive bites, and frequently the spider drives the human off just by the mechanical pain of its bite, thus it is not unusual for humans to receive dry bites or partial envenomations. Thus, most spiders are unlikely to otherwise bite humans because they do not identify humans as prey. Some spiders (including highly venomous species like the [[Brazilian wandering spider]]) ''will'' behave aggressively towards large animals (including people) that the spider perceives as a threat. Even in those cases, however, they will first make a determined threat display and will bite only if they have no other choice. Spiders of the genus ''[[Phoneutria]]'' have extremely toxic venom and approximately ten times as much venom as other spiders that are known to produce fatalities in adult humans<ref>Simó, Miguel & Brescovit, D. Antonio,
"Revision and cladistic analysis of the Neotropical spider genus ''Phoneutria'' Perty, 1833 (Araneae, Ctenidae), with notes on related Cteninae" - ''Bulletin British Arachnology Society'' (2001) 12 (2) 67-82</ref> , but serious consequences from their bites are not common, as many bites received by humans are believed to be dry or of low volume.<ref>[http://www.scielo.br/scielo.php?pid=S0036-46652000000100003&script=sci_arttext&tlng= Revista do Instituto de Medicina Tropical de São Paulo - A clinico-epidemiological study of bites by spiders of the genus Phoneutria<!-- Bot generated title -->]</ref>
Many bites occur when a person steps on a spider, or inserts a limb into an article of clothing that the spider occupies. Even small spiders may deliver painful bites to people when pinched. For instance, ''[[Phidippus audax]]'' – a common [[jumping spider]], which may grow to be approximately 3/8 inch (1 cm) long – is capable of inflicting a bite that is about as painful as a bee sting when pinched between the folds of a human's palm or otherwise seriously annoyed.
==Spider venom==
The chief concern with the bite of medically significant spiders is the effect of the spider's [[venom]]. A '''spider envenomation''' occurs whenever a [[spider]] bites someone and chooses to inject [[venom]] into the wound. Not all spider bites involve injection of venom into the wound, and the amount of venom injected can vary based on the type of spider and the circumstances of the encounter. With very few exceptions, such as the so-called [[camel spider]] (which is not a true spider), 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, and other species are known to consume prey which is already dead, which also may pose a risk for transmission of infectious [[bacteria]] from a bite. <ref name="CamelSpider">
{{cite book|
author=Punzo, Fred|
title=The Biology of Camel-Spiders|
publisher=Kluwer Academic Publishers|
date=1998}}</ref> However, it is generally the toxicity of spider venom which poses the most risk to human beings; several spiders are known to have venom which can be fatal to humans in the amounts that a spider will typically inject when biting.
All spiders are capable of producing venom, with the exception of the [[hackled orb-weaver]]s, the ''[[Holarchaeidae]]'', and the primitive ''[[Mesothelae]]''. (Other arachnids often confused with spiders, such as the [[harvestman]] and [[sun spider]]s, also do not produce venom). Nonetheless, only a small percentage of species have bites which 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 which is sufficiently toxic (in the quantities delivered) to require medical attention, and of those only a few are known to produce fatalities.
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).
===Neurotoxicvenom ===
The majority of spiders with serious bites possess a [[neurotoxin|neurotoxic]] venom of some sort, though the specific manner in which the [[nervous system]] is attacked varies from spider to spider.
*[[Widow spider]] venom contains components known as [[latrotoxin]]s, which cause the release of the [[neurotransmitter]] [[acetylcholine]], stimulating muscle contractions. This can affect the body in several ways, including causing painful abdominal cramps, as well as interfering with [[Respiratory system|respiration]], and causing other systemic effects. <ref name="Global"/>
*The venom of [[Australasian funnel-web spider]]s and [[mouse spider]]s works by opening [[sodium channel]]s, causing excessive neural activity which interferes with normal bodily function.
*The venom of [[Brazilian wandering spider]]s is also a potent neurotoxin, which attacks multiple types of [[ion channel]]s <ref>{{cite journal|
author=Marcus V. Gomez, Evanguedes Kalapothakis, Cristina Guatimosim, 2 and Marco A. M. Prado|
title=''Phoneutria nigriventer'' Venom: A Cocktail of Toxins That Affect Ion Channels|
journal=Cellular and Molecular Neurobiology|
volume=22|
issue=5-6|
url=http://www.springerlink.com/(eacd0z55ulayxd55peepg445)/app/home/contribution.asp?referrer=parent&backto=issue,11,32;journal,23,131;linkingpublicationresults,1:102583,1
}}</ref> In addition, the venom contains high levels of [[serotonin]], making an envenomation by this species particularly painful.
===Necrotic venom===
Spiders known to have [[necrotoxin|necrotic]] venom are found in the family ''[[Sicariidae]]'', a family which includes both the [[recluse spider]]s and the [[six-eyed sand spider]]s. Spiders in this family possess a known dermonecrotic agent [[sphingomyelinase D]], which is otherwise found only in a few pathogenic bacteria. 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 ''Sicariidae'' spiders such as the [[brown recluse]]<ref>{{cite journal|
author=Greta J. Binford and Michael A. Wells|
title=The phylogenetic distribution of sphingomyelinase D activity in venoms of Haplogyne spiders|
journal=Comparative Biochemistry and Physiology Part B|
volume=135|
date=2003|
pages=25–33|
url=http://www.lclark.edu/~binford/SMDDistribution%20copy.pdf|
format=pdf
}}</ref>. 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.<ref>{{cite journal|
author=Schenone H, Saavedra T, Rojas A, Villarroel F.|
title=Loxoscelism in Chile. Epidemiologic, clinical and experimental studies|
journal=Revista do Instituto de Medicina Tropical de São Paulo|
volume=31|
date=1989|
pages=403–415|
url=http://bases.bireme.br/cgi-bin/wxislind.exe/iah/online/?IsisScript=iah/iah.xis&nextAction=lnk&base=MEDLINE_1966-1995&exprSearch=2577020&indexSearch=UI&lang=i }}</ref> Even in the absence of systemic effects, serious bites from ''Sicariidae'' spiders may form a necrotising [[ulcer]] that destroys soft tissue and may take months and very rarely years to heal, leaving deep [[scar]]s. The damaged tissue may become [[gangrene|gangrenous]] and eventually slough away. Initially there may be no pain from a bite, 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.<ref name="ClinTox-Wasserman">{{cite journal | author = Wasserman G, Anderson P | title = Loxoscelism and necrotic arachnidism | journal = J Toxicol Clin Toxicol | volume = 21 | issue = 4-5 | pages = 451–72 | year =1983–1984 | pmid = 6381752}}</ref>
Serious systemic effects may occur before this time, as the venom spreads throughout the body in minutes. Mild symptoms include [[nausea]], [[vomiting]], [[fever]], [[rash]]es, and muscle and joint pain. Rarely more severe symptoms occur including [[hemolysis]], [[thrombocytopenia]], and [[disseminated intravascular coagulation]].<ref name="NEJM2005-Wasserman">{{cite journal | author = Wasserman G | title = Bites of the brown recluse spider. | journal = N Engl J Med | volume = 352 | issue = 19 | pages = 2029–30; author reply 2029–30 | year = 2005 | pmid = 15892198 | doi = 10.1056/NEJM200505123521922}}</ref> 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.''
Numerous other spiders have been associated with necrotic bites in the medical literature. Examples include the [[hobo spider]] and the [[yellow sac spider]]. However, the bites from these spiders are not known to produce the severe symptoms that often follow from a recluse spider bite, and the level of danger posed by each has been called into question.<ref>
{{cite journal|
author=Bennett, R. G. and R. S. Vetter.|
title=An approach to spider bites: erroneous attribution of dermonecrotic lesions to brown recluse and hobo spider bites in Canada|
journal=Canadian Fam Physician|
date=2004|
volume=50|
pages=1098–1101
}}</ref><ref>{{cite journal|
author=James H. Diaz, MD|
title=Most necrotic ulcers are not spider bites|
url=http://www.ajtmh.org/cgi/content/full/72/4/364|
journal=American Journal of Tropical Medicine and Hygiene|
volume=72|
issue=4|
date=2005|
pages=364–367
}}</ref> 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 danger 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. <ref name="WhiteTail">{{cite journal|
author=Isbister GK, Gray MR|
title=White-tail spider bite: a prospective study of 130 definite bites by Lampona species|
journal=Medical Journal of Australia|
volume=179|
issue=4|
pages=199–202|
url=http://www.mja.com.au/public/issues/179_04_180803/isb10785_fm.html
}}</ref><ref>{{cite journal|
author=Isbister GK, Hirst D|
title=A prospective study of definite bites by spiders of the family Sparassidae (huntsmen spiders) with identification to species level|
journal=[[Toxicon]]|
volume=42|
issue=2|
date=2003-08|
pages=163–71|
url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12906887&dopt=Abstract|
type=abstract|
doi=10.1016/S0041-0101(03)00129-6
}}</ref>
==Treatment==
Treatment for bites depends on the type of spider in question. Most spider bites are harmless, and will require no first aid. If you experience major discomfort and require medical treatment, and a spider was observed in the act of biting, then a spider expert may be needed to determine the species of spider that has bitten you--identification of the spider's species might determine the proper course of treatment. For this reason it is preferable to capture the spider--either alive, or in a well-preserved condition. Spiders which have been flattened, or which are allowed to desiccate or decay, may not be useful in achieving a positive identification. Most medical responders are not trained to identify spiders, and few hospitals have spider experts on staff. Contrary to media reports, it is not (in general) possible to identify the type of spider responsible for a bite solely from observed symptoms.
Unless a spider is observed in the act of biting, it should not be assumed that a spider bite has occurred (or that a wound, injury, or illness was caused by a spider). Assumption that a reported injury was caused by a spider is the most common source of false reports, which in some cases have often led to misdiagnosis and mistreatment, with potentially life-threatening consequences<ref>Vetter, R. S. (2000). Myth: Idiopathic wounds are often due to brown recluse or other spider bites throughout the United States. ''[[Western Journal of Medicine]]'' 173:357-358</ref>. 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, in such cases the spider is usually no longer present.
Treatments for more minor bites should be as for any puncture wound. The wound should first be encouraged to bleed to wash out any foreign material and debris. (Many wounds will not bleed because they are so small in diameter that they seal immediately.) Topical antiseptics such as Isodine should be applied on the off chance that the bite introduced some virus or microbe beneath the skin level and that the antiseptic can penetrate to that depth. The bite should be observed for a couple of days so that medical attention can be sought if signs of infection appear. (It is obviously difficult to get antiseptic to penetrate to the bottom of such a puncture.)<ref>Wilkerson, James A., M.D. (1967). ''Medicine for Mountaineering'', Seattle. p. 50</ref> First aid may also involve the application of an ice pack to control [[inflammation]], the application of aloe vera to soothe and help control the pain, and if serious symptoms appear, prompt medical care.
In the case of bites by [[widow spider]]s, [[Australian venomous funnel-web spider]]s, or [[Brazilian wandering spider]]s, prompt medical attention should be sought; in some cases the bites of these spiders may develop into a [[medical emergency]]. Medical attention should also be sought if a severe [[allergic reaction]] occurs.{{Fact|date=February 2007}}
===Necrotic bites===
There is no established treatment for [[necrosis]]. Routine treatment should 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]], [[surgery|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.<ref name="NEJM2005-Vetter">{{cite journal | author = Swanson D, Vetter R | title = Bites of brown recluse spiders and suspected necrotic arachnidism. | journal = N Engl J Med | volume = 352 | issue = 7 | pages = 700–7 | year = 2005 | pmid = 15716564 | doi = 10.1056/NEJMra041184}}</ref>
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.<ref>{{cite web|url=http://www.aafp.org/fpr/20041100/10.html|title=If the patient says spider bite, think [[MRSA]], says Assembly speaker|author=Peggy Peck|date=November 2004|accessdate=[[October 11]], [[2007]]|publisher=American Academy of Family Physicians}}</ref>
===Specific treatments===
Some specific courses of treatment may be indicated to deal with severe symptoms:
*[[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.<ref name="AmJEmergMed2003-Bryant">{{cite journal | author = Bryant S, Pittman L | title = Dapsone use in Loxosceles reclusa envenomation: is there an indication? | journal = Am J Emerg Med | volume = 21 | issue = 1 | pages = 89–90 | year = 2003 | pmid = 12563594 | doi = 10.1053/ajem.2003.50021}}</ref>
*Wound infection is rare. [[Antibiotics]] are not recommended unless there is a credible diagnosis of infection.<ref name="MoMed1998-Anderson">{{cite journal | author = Anderson P | title = Missouri brown recluse spider: a review and update | journal = Mo Med | volume = 95 | issue = 7 | pages = 318–22 | year = 1998 | pmid = 9666677}}</ref>
*Studies have shown surgical intervention is ineffective and may worsen outcome. Excision may delay wound healing, cause [[abscesses]], and lead to objectional scarring.<ref name="AnnSurg1985-Rees">{{cite journal | author = Rees R, Altenbern D, Lynch J, King L | title = Brown recluse spider bites. A comparison of early surgical excision versus dapsone and delayed surgical excision | journal = Ann Surg | volume = 202 | issue = 5 | pages = 659–63 | year = 1985 | pmid = 4051613}}</ref>
*[[Anecdotal evidence]] suggests that application of [[Glyceryl trinitrate#Uses|nitroglycerin]] patches may be effective in treating recluse bites.<ref>{{cite web | author=Burton K |title=The Brown Recluse Spider: Finally stopped in its tracks | url=http://www.geocities.com/Yosemite/Forest/2021/recluse/intro.html | accessdate=2006-09-02}}</ref> Recluse venom is a vasoconstrictor, and nitroglycerin causes [[vasodilation]], allowing the venom to be diluted into the bloodstream, and fresh blood to flow to the wound. Theoretically this prevents necrosis, as vasoconstriction may contribute to necrosis. However, one scientific animal study found no benefit in preventing necrosis, with results showing it increased inflammation and it caused symptoms of systemic envenoming. The authors concluded the results of the study did not support the use of topical nitroglycerin in brown recluse envenoming.<ref name="AnnEmergMed2001-Lowry">{{cite journal | author = Lowry B, Bradfield J, Carroll R, Brewer K, Meggs W | title = A controlled trial of topical nitroglycerin in a New Zealand white rabbit model of brown recluse spider envenomation | journal = Ann Emerg Med | volume = 37 | issue = 2 | pages = 161–5 | year = 2001 | pmid = 11174233 | doi = 10.1067/mem.2001.113031}}</ref>
*Use of [[antivenom]] for severe spider bites is frequently indicated, especially in the case of neurotoxic venoms. Effective antivenoms exist for ''Latrodectus'', ''Atrax'', and ''Phoneutria'' venom. Recluse bites are now treatable by antivenom; an antivenom for ''Loxosceles'' bites is now 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.<ref name="ClinTox2003-Isbister">{{cite journal | author = Isbister G, Graudins A, White J, Warrell D | title = Antivenom treatment in arachnidism | journal = J Toxicol Clin Toxicol | volume = 41 | issue = 3 | pages = 291–300 | year = 2003 | pmid = 12807312 | doi = 10.1081/CLT-120021114}}</ref> Due to the risk of [[serum sickness]], use of antivenom is generally not indicated unless serious symptoms are present, and/or the patient fails to respond to other forms of treatment.
==Types of spiders with medically significant venom==
Spiders having medically significant venom exist in almost all parts of the world except those that are coldest. 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.
The following types of spiders are known to have medically significant bites, with symptoms ranging from localized [[Pain and nociception|pain]] all the way to severe [[biological tissue|tissue]] destruction and potential [[death]]. Spiders whose bite has 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]]''.
===Brazilian wandering spiders (''Phoneutria''--confirmed deaths)===
{{main|Brazilian wandering spider}}
The [[Brazilian wandering spider]] (a ctenid spider) is a large, brown spider rather like a North American [[Wolf spider]] in appearance. However, it has a highly toxic venom (one of the most neurologically active), and is regarded (along with the [[Australian venomous funnel-web spiders]] below) as among the most dangerous spiders in the world.<ref>[http://www.nature.com/bjp/journal/v139/n1/full/0705240a.html British Journal of Pharmacology - Phoneutria nigriventer spider venom activates 5-HT4 receptors in rat-isolated vagus nerve<!-- Bot generated title -->]</ref> It, like several other more harmless spiders, may hitch a ride in clusters of [[banana]]s. As a result, any large spider appearing in a bunch of bananas should be treated with due care. Oddly, many of the bites of this species are alleged to be dry bites (in which no venom is released), but because of the margin of error when identifying the precise subspecies involved (assuming the spider body is saved or captured), this claim is not definitive. In either case, the bite is at minimum mechanically painful due to the large size of the chelicerae (fangs), and the high levels of [[serotonin]] contained in the venom. The bite can be one of the most excruciating of all spider envenomations. The spiders are as large as some small tarantulas and, as already mentioned, have fairly long fangs. While venom from either spider can be deadly to children and the infirm, since the development of [[antivenom]] to the venoms of both were developed (the funnel web spider in the mid-1980s and the wandering spider in 1996{{Fact|date=February 2008}}<!--This contradicts the information in the Brazilian wandering spider wiki article-->), no human deaths from their bites have been recorded. Nevertheless, any large spider which makes a threat display (raising front legs, rearing back to display fangs) when encountered should be treated with caution - especially in areas where this type of spiders may be present.
This spider's venom has also been found to cause increased levels of Nitric Oxide, which, in male human victims, will result in an involuntary erection that can be very painful and last hours. Scientists are attempting to create an erectile dysfunction treatment that can be combined with other medicines out of the peptide that causes this reaction.
===Australian venomous funnel-web spiders (''Atrax'', ''Hadronyche''--confirmed deaths)===
{{main|Australian venomous funnel-web spiders}}
[[Image:Victorian funnelweb.jpg|thumb|left|''Atrax robustus'' <br>Sydney Funnel-web Spider]]
The '''Australian venomous funnel-web spiders''', such as the '''Sydney funnel-web spider''' (a [[mygalomorph]] only distantly related to the [[araneomorph]] funnel-web spiders) frequently bite people and are regarded as among the most dangerous in the world. They are quite aggressive spiders, and are prone to biting when confronted, rather than running away. The Sydney funnel-web spider, a large, bulky, black spider, is restricted to a relatively small area around [[Sydney]], [[Australia]]. Its venom contains a compound known as ''robustotoxin'' 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.
[[Image:Sketch Funnel-Web range.gif|thumb|right|Range of the two genera (Hadronyche and Atrax) of venomous Australian funnel-web spiders]]
There are other dangerous species of ''Atrax'' and ''Hadronyche'' related to this spider in surrounding parts of Australia, including 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.
One other genus in the ''[[Hexathelidae]]'' family has been reported to cause severe symptoms in humans. The genus ''[[Macrothele]]'' in [[Taiwan]] has been attributed to severe bites, but no fatalities.<ref name="Taiwan">
{{cite journal|
author=Hung, Shin-Wen and Wong, Tzong-Leun|
title=Arachnid Envenomation in Taiwan|
journal=Ann. Disaster Med|
volume=3 Suppl. 1|
pages=S12–S17|
url=http://www.disaster.org.tw/chinese/annmed/Vol3supp1/3.pdf
}}</ref> There are no known deaths attributed in the literature to any funnel-web species other than ''A. robustus''
===Tangle-web spiders (''Theridiidae'')===
Two genera of the [[tangle web spider]]s have venom which is known to be medically significant. One genus, the '''[[widow spider]]s''' 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.
====Widow spiders (''Latrodectus''--confirmed deaths)====
{{main|Widow spider}}
<!-- Image with unknown copyright status removed: [[Image:2 4bla.jpg|thumb|left|''Latrodectus mactans'', the black widow]] -->
The '''widow spiders''' (genus ''[[Latrodectus]]''), such as the [[Black widow spider|black widow]] and [[redback spider]], are spiders that carry a [[neurotoxic]] [[Venom (poison)|venom]] [http://ohioline.osu.edu/hyg-Fact/2000/2061A.html] which can cause a set of symptoms known as '''[[Latrodectism]]'''. 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 spiders, 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 considered to be much less dangerous (if at all) than the females. Widows tend to be quite non-aggressive, but will bite if the web is disturbed and the spider feels threatened. The venom, although rarely life-threatening, produces very painful effects including muscle spasms and 'tetanus-like' contractions. A serious bite will often require a short hospital stay. Children, elderly, and ill individuals are at most risk of serious effects.
====False black widows (''Steatoda'')====
{{main|Steatoda}}
[[Image:Steatoda bipunctata female (aka).jpg|thumb|right|Steatoda bipunctata]]
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 spider]]s in size and physical form, which is not surprising since they are members of the same Family. While the bite of ''Steatoda'' spiders are 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 ''[[Steatoda nobilis|S. nobilis]]'', and a species found mainly in New Zealand and South Africa, ''S. capensis''
Use of widow spider [[antivenom]] has been shown effective in treating steatodism.<ref>{{cite journal | author = Graudins A, Gunja N, Broady K, Nicholson G | title = Clinical and in vitro evidence for the efficacy of Australian redback spider (Latrodectus hasselti) antivenom in the treatment of envenomation by a Cupboard spider (Steatoda grossa) | journal = Toxicon | volume = 40 | issue = 6 | pages = 767–75 | year = 2002 | pmid = 12175614 | doi = 10.1016/S0041-0101(01)00280-X}}</ref> 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.
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.They look something like this: <big>'''Ə'''</big> 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.
===Sicariidae spiders===
The family ''[[Sicariidae]]'' includes two genera, both of which have highly dangerous and [[necrotoxic]] bites. One genus, ''Loxosceles'', are the well-known recluse spiders, a genus which is distributed worldwide (but is most commonly found in the Americas). The other genus, ''Sicarius'', is far less known; being found only in the Southern Hemisphere. Spiders in both genera have venom containing the dermonecrotic compound [[sphingomyelinase D]].
====Recluse spiders (''Loxosceles''--confirmed deaths)====
<!-- Commented out because image was deleted: [[Image:brown recluse.jpg|thumb|right|180px|Brown recluse (photo courtesy of the [[University of Nebraska-Lincoln]])]] -->
{{main|Recluse spider}}
'''Recluse spiders''' (''Loxosceles spp.''), such as the [[brown recluse spider]], also known as "violin spiders" or "fiddlers" 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 2/3 of the country by the eastern 3/4 of the country. A number of related recluse spiders (some non-native introductions) are found in southern California and nearby areas, as well.
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.
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 [[scar]]s. The damaged tissue will become [[gangrene|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.<ref name="ClinTox-Wasserman">{{cite journal | author = Wasserman G, Anderson P | title = Loxoscelism and necrotic arachnidism | journal = J Toxicol Clin Toxicol | volume = 21 | issue = 4-5 | pages = 451–72 | year =1983–1984 | pmid = 6381752}}</ref>
Serious systemic effects may occur before this time, as the venom spreads throughout the body in minutes. Mild symptoms include [[nausea]], [[vomiting]], [[fever]], [[rash]]es, and muscle and joint pain. Rarely more severe symptoms occur including [[hemolysis]], [[thrombocytopenia]], and [[disseminated intravascular coagulation]].<ref name="NEJM2005-Wasserman">{{cite journal | author = Wasserman G | title = Bites of the brown recluse spider. | journal = N Engl J Med | volume = 352 | issue = 19 | pages = 2029–30; author reply 2029–30 | year = 2005 | pmid = 15892198 | doi = 10.1056/NEJM200505123521922}}</ref> 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.''
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. <ref>{{cite journal|
author=Schenone H, Saavedra T, Rojas A, Villarroel F.|
title=Loxoscelism in Chile. Epidemiologic, clinical and experimental studies|
journal=Revista do Instituto de Medicina Tropical de São Paulo|
volume=31|
pages=403–415|
date=1989|
url=http://bases.bireme.br/cgi-bin/wxislind.exe/iah/online/?IsisScript=iah/iah.xis&nextAction=lnk&base=MEDLINE_1966-1995&exprSearch=2577020&indexSearch=UI&lang=i
}}</ref>
====Six eyed sand spiders (''Sicarius'')====
{{main|Six-eyed sand spider}}
[[Image:Six-eyed sand spider 4.jpg|thumb|left|The Six-eyed sand spider]]
The '''six-eyed sand spider''', of southern [[Africa]] (and other spiders in the genus ''Sicarius''), is considered by some to be the world's most venomous spider. Assays of its venom have led some to consider this spider's bite as the most dangerous on record; and currently no [[antivenom]] exists for its bite. Fortunately, this specimen rarely interacts with humans, and is seldom known to bite; recorded envenomations by this spider are rare. A cousin of the [[recluse spider]] (and possessing the same toxic compound as found in recluse venom), this spider buries itself in the sand and strikes from ambush at prey that wanders too closely. 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.
Little is known about the bite of other ''Sicarius'' species; however numerous other species have also been found to possess venom containing [[sphingomyelinase D]].
===Mouse spiders (''Missulena'')===
{{main|mouse spider}}
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 ''robustotoxin'', 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,<ref name="MJA2005-Isbister">{{cite journal | author = Isbister G, Gray M, Balit C, Raven R, Stokes B, Porges K, Tankel A, Turner E, White J, Fisher M | title = Funnel-web spider bite: a systematic review of recorded clinical cases | journal = Med J Aust | volume = 182 | issue = 8 | pages = 407–11 | year = 2005 | pmid = 15850438}}</ref> 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.<ref>{{cite journal|
author=Ibister GK|
title=Mouse spider bites (Missulena spp) and their medical importance|
journal=Medical Journal of Australia|
volume=180|
issue=5|
date=2004|
pages=225–227|
url=http://www.mja.com.au/public/issues/180_05_010304/isb10842_fm.html
}}</ref>
===True tarantulas (''Theraphosidae'')===
{{main|Tarantula}}
The true '''tarantulas''', of the family ''Theraphosidae'', are fearsome looking spiders with somewhat notorious reputations. As large spiders, they have very powerful fangs and are capable of delivering a sizable quantity of venom. However, many species of tarantula are known to be relatively harmless to humans. Tarantulas are typically divided between '''New World''' and '''Old World''' types; depending on what part of the world the spider in question comes from.
====New world tarantulas====
[[Image:Brachypelma edit.jpg|thumb|left|Mexican Red Knee tarantula (''Brachypelma sp''), a New World species]]
New World tarantulas--those indigenous to the Americas--have bites that generally pose little threat to humans (other than causing localized pain). The primary means of defense for these spiders are [[urticating hair]]s, which can cause irritation and other typical symptoms in humans.
====Old world tarantulas====
[[Image:Haplopelma lividum1.jpg|thumb|right|Cobalt blue tarantula (''Haplopelma lividum''), an Old World species]]
Old World tarantulas, especially those indigenous to [[Asia]], are another matter. These species lack [[urticating hair]]s, and use biting as a defensive mechanism (as well for subduing prey). In addition, these spiders are far less docile; and more likely to try to bite an adversary (including humans) if provoked. The effect of Old World tarantula venoms is not well studied, for the most part; however much anecdotal evidence suggests they have stronger venom than their New World counterparts.
There are many anecdotal reports from individuals in the tarantula pet trade of significant bite from ''[[Poecilotheria]] spp.'', 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.<ref>{{cite journal
| last = Gabriel,
| first = R.
| title = Notes and Observations Regarding the Bite of Poecilotheria pederseni
| journal = British Tarantula Society Journal
| volume = 17
| issue = 2
| pages = 61–64
| date = [[2002]]
| url = http://www.thebts.co.uk/Bite_ppederseni.htm }}</ref><ref>[http://www.arachnoboards.com/ab/showthread.php?t=78009 Poecilotheria metallica - Arachnoboards<!-- Bot generated title -->]</ref><ref>[http://www.bighairyspiders.com/bites.shtml#ppederseni Phong's Tarantulas! - Tarantula bites<!-- Bot generated title -->]</ref><ref>Schmidt, G. (1988): Wie gefährlich sind Vogelspinnenbisse ? Deutsches Ärzteblatt 85 Heft 28/29(2): 1424-1425.
(u. a. Infos about Poecilotheria fasciata)</ref>
One species whose venom has been studied extensively is the [[Chinese bird spider]] (''Haplopelma spp.''), 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.
===Yellow sac spiders (''Chiracanthum'')===
{{main|Yellow sac spider}}
<!-- Commented out because image was deleted: [[Image:Yellowsacspider.jpg|thumb|left|[[Yellow sac spider]] (Body length 8–9 mm)]] -->
The '''yellow sac spiders''', ''Chiracanthum 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.
===Huntsman spiders (''Heteropoda'')===
{{main|Huntsman spider}}
[[Image:HuntsmanXcricket.jpg|left|thumb|Huntsman spider (Heteropoda venatoria) eating a cricket]]
The '''huntsman spiders''' have a worldwide reputation for scaring people. They are large, defend their nests, and may move toward people and make threat displays. They frequently enter houses and hunt over the walls and ceilings where they may run rapidly for long distances without pausing. When they actually do bite people, the bites are very unpleasant, but these spiders are not regarded as dangerous. They are quite common in parts of Australia. Australian huntsman spiders are typically non-aggressive except when defending their nests or their young.
There is one spider in California and Japan, probably a huntsman (tentatively identified as a member of the Sparassidae family, ''Heteropoda venatoria''), which might run over and bite your finger if you touch the wall that it is clambering over.{{Fact|date=June 2008}} That behavior may well occur because its eyesight is good enough to see movement and general shape, but not sufficient to avoid mistaking something else for its natural prey. In general, however, members of this genus scramble wildly to escape when they become aware of a human moving into their vicinity.
===Redback jumping spiders (''Phidippus johnsoni'')===
{{main|Redback jumping spider}}
[[Image:P johnsoni PEM1.jpg|thumb|left|Female ''Phidippus johnsoni'' (?) 14 mm]]
Some people have reported being bitten by '''redback jumping spiders,''' one of the visually most prominent species among the genus Phidippus. Many reports come from California, although their range is much wider, and people elsewhere may have unpleasant contacts with them. These relatively large, alert but slow-moving jumping spiders have bright red abdomens (the females have a black stripe), and should be clearly visible. It is unclear how bites to humans occur. Accidental contact seems rather unlikely since jumping spiders have excellent vision and can easily avoid being brushed by a human hand. It is also unlikely that they would mistake a human finger for their natural prey. One source suggests that, since they are quite attractive, children may try to pick them up and in that way elicit a defensive bite. Since these spiders are quite large, their body length being around 12 mm (1/2 inch), the volume of their available venom is accordingly rather large. Fortunately, however, the worst consequences reported have been three to four days of discomfort, with no permanent damage. Like most of the larger spiders, the consequences of a bite seem little different from those of a wasp or bee sting. Since they do not frequent human habitations it should ordinarily be easy to avoid unpleasant contact with them. Even when encountered the ability of jumping spider to detect and track human movement should prevent most potential bite situations.
{{clear}}
==Comparative analysis==
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:
*First, 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.
*Second, there have been reports of spider bites (by spiders considered otherwise harmless) causing [[allergic reaction]]s in some individuals, up to and including [[Anaphylaxis|anaphylactic shock]], 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).<ref name="Vetter">{{cite journal|
author=Vetter, Richard S. and Visscher, P. Kirk, Department of Entomology, University of California, Riverside, CA 92521 USA|
title=Bites and Stings of medically important venomous arthropods|
journal=International Journal of Dermatology|
volume=37|
pages=481–496|
date=1998-07|
url=http://spiders.ucr.edu/dermatol.html|
doi=10.1046/j.1365-4362.1998.00455.x
}}</ref>
<!-- not a good reference<ref>http://www.cdc.gov/nasd/docs/d000001-d000100/d000039/d000039.html</ref>-->
*Third, 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 should also be noted that, for healthy adults, a bite by even the most toxic spiders on the list may require hours before death ensues; if timely appropriate emergency medical treatment is administered, victims may be expected to recover. The scenario given in movies such as ''[[Arachnophobia (film)|Arachnophobia]]'', where bite victims die within minutes, does not occur. One exception to this picture occurs because in the case of very small children 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 event occurred before the development of an [[antivenom]]. Since the antivenom was developed there have been no fatalities due to this species.
The spiders believed to be most dangerous to humans, in terms of the risk posed by a bite, are the [[Australasian funnel-web spider|Sydney funnel-web spiders]] and [[Brazilian wandering spider]]. These spiders are potentially more dangerous than [[widow spider]]s because they have longer fangs and possess greater quantities of venom, thus they are capable of injecting far more 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. ''Atrax robustus'' has approximately 1.7 mg of venom. Bites of [[six-eyed sand spider]]s are thought likely to be even more dangerous to humans than any of the others, but fortunately there have been very few bites. Two instances of human envenomation are known; one was fatal, and the other involved the loss of an arm. This, along with venom testing in rabbits, leads some experts to believe that Sicarius may be the most harmful spider envenomation known, as no other species has an ''observed'' 50% lethality rate.
By general agreement, spiders of the genus [[Latrodectus]] (of which the Black Widow spider is the most notorious) kill more people per year, worldwide, than any other spider.{{Fact|date=February 2007}} Because they are so small, they are much harder to detect than a large Brazilian Wandering Spider or a Tarantula. Though their venom is extremely potent, these spiders are not especially large. 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 (approx. .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). When this small amount of venom is diffused throughout the body of a healthy, mature human, it usually does not amount to a fatal dose. Deaths in healthy adults from ''Latrodectus'' bites are rare in terms of the number of bites per thousand people. Only sixty-three deaths were reported in the United States between 1950 and 1989 (Miller, 1992). 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, so the highest number of deaths worldwide are caused by members of the genus Latrodectus. Widow spiders have more potent venom than most spiders, and prior to the development of [[antivenom]], 5% of bites resulted in fatalities.<ref>{{cite journal | author = Bettini S | title = Epidemiology of Latrodectism | journal = Toxicon | volume = 104 | issue = | pages = 93–102 | year = | pmid = 14301291}}</ref>
===Measurements===
The LD-50 figures have limited utility since the effects of venoms differ widely from species to species. The [[University of California]] at [[Riverside]] reports that prior to the development of an antivenom, 5% of victims of widow spiders would die, but comparable figures are not available for the other species. Before an antivenom was developed, deaths from Atrax and Hadronyche were very common. 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.
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. Nevertheless, any venom capable of killing other organisms in small doses should be avoided by 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.
{| border="1" cellpadding="2" cellspacing="0"
|- align="left" style="background-color: #cccccc;"
! Genus
! Species
! Common name
! Body length
! Venom amount
! LD-50
! Alternate LD-50
! Deaths reported
|-
| Atrax
| robustus
| [[Australasian funnel-web spider|Venomous funnel-web]]
| 24–32 mm. <ref name="Vetter"/>
| 0.25 mg (F) and 0.81 mg (M) <ref name="inchem">
{{cite web|
authors=While, Julian and Gray, Michael|
title=Atrax Robustus|
work=IPCS INCHEM|
publisher=International Programme on Chemical Safety |
url=http://www.inchem.org/documents/pims/animal/atrax.htm|
date=1989}}</ref> 2 mg <ref name="NIH">{{cite journal|
author=Sutherland SK, Duncan AW, and Tibballs J.|
title=Local inactivation of funnel-web spider (''Atrax robustus'') venom by first-aid measures: potentially lifesaving part of treatment|
journal=Medical Journal of Australia|
volume=2|
issue=8|
date=1980-10-18|
pages=435–437|
url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7207322&dopt=Abstract|
}}</ref>
| .16 mg/kg <ref name="Sheumack">{{cite journal|
author=Sheumack DD, Baldo BA, Carroll PR, Hampson F, Howden ME, Skorulis A|
title=A comparative study of properties and toxic constituents of funnel web spider (Atrax) venoms|
journal=Comparative biochemistry and physiology|
date=1984|
volume=78|
issue=1|
pages=55–68|
url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=6146485&dopt=Citation
}}</ref>
| unknown
| 1927–1980 13 deaths
|-
| Hadronyche
| species
| [[Australasian funnel-web spider|Venomous funnel-web]]
| 24–32 mm. <ref name="Vetter"/>
| 0.25 mg (F) and 0.81 mg (M) <ref name="inchem"/> 2 mg <ref name="NIH"/>
| .16 mg/kg <ref name="Sheumack"/>
|
|
|-
| [[Latrodectus]]
| mactans
| [[Black widow spider|Black widow]]
| 8–15 mm <ref name="Vetter"/>
| 0.02–.03 mg. <ref name="Stewart">{{
cite paper|
author=Stewart, Charles|
title=Beyond the Road: Environmental Emergencies for Emergency Service Providers|
publisher=Charles Stewart and Associates|
date=1998|
url=http://www.storysmith.net/Articles/Bites%20and%20stings.pdf}}
</ref> <ref name="THU">http://www.thudiv.com/variety/spider/spider1.htm) (Tung Hai University, Taiwan, article in Chinese '''broken link''')</ref>
| 0.002 mg/kg <ref name="Stewart"/>*
| 0.9 mg/kg
| 5% of reported bites prior to [[antivenom]] availability <ref name="Vetter"/>
|-
| [[Latrodectus]]
| tredecimguttatus
| [[Latrodectus tredecimguttatus|Malmignatte]]
| (approx. same)
| (approx. same)
| 0.68 μg/kg <ref name="Nifty">{{cite journal|
author=Ori, Masahisa and Ikeda, Hiroyoshi|
title=Spider Venoms and Spider Toxins|
journal=Jounal of Toxicology.Toxin reviews|
volume=17|
issue=3|
date=1998|
pages=405–426|
url=http://homepage3.nifty.com/~hispider/spidervenom.txt
}}</ref>
| 16.25 μg/kg <ref name="Nifty"/>
|
|-
| Loxosceles
| Reclusa
| [[Brown recluse]]
| 1.2 cm (0.75 in) <ref name="Vetter"/>6–10 mm <ref name="Vetter"/>
| .13–.27 mg. <ref name="Manzoli">{{cite journal|
author=M. F. Manzoli-Palma; N. Gobbi; M. S. Palma|
title=Insects as biological models to assay spider and scorpion venom toxicity|
journal=Journal of Venomous Animals and Toxins including Tropical Diseases|
volume=9|
issue=2|
date=2003|
url=http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-91992003000200004
}}</ref> <ref name="Nifty"/>
|
|
| (rare) <ref name="Vetter"/>
|-
| Loxosceles
| intermedia
|
|
|
| 0.48 mg/kg <ref name="NIH2">{{cite journal|
author=Barbaro KC, Ferreira ML, Cardoso DF, Eickstedt VR, Mota I|
title=Identification and neutralization of biological activities in the venoms of Loxosceles spiders|
journal=Brazilian Journal of Med Biol Res|
date=1996-11|
volume=29|
issue=11|
pages=1491–7|
url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9196551&dopt=Abstract
}}</ref>
|
| unknown
|-
| Loxosceles
| laeta
| [[Chilean recluse]]
|
|
| 1.45 mg/kg <ref name="NIH2"/>
|
|
|-
| Loxosceles
| gaucho
|
|
|
|0.74 mg/kg <ref name="NIH2"/>
|
|
|-
| Phoneutria
| bahiensis
| [[Brazilian wandering spider]]
| 30 mm
| 1.079 mg <ref name="Herzig-toxicon">{{cite journal | author = Herzig V, John Ward R, Ferreira dos Santos W | title = Intersexual variations in the venom of the Brazilian 'armed' spider Phoneutria nigriventer (Keyserling, 1891) | journal = Toxicon | volume = 40 | issue = 10 | pages = 1399–406 | year = 2002 | pmid = 12368110 | doi = 10.1016/S0041-0101(02)00136-8}}</ref>
| .00061–.00157 mg/kg <ref name="Herzig-toxicon"/>
|
|
|-
| Phoneutria
| boliviensis
| [[Brazilian wandering spider]]
| 30 mm
| 1.079 mg. <ref name="Herzig-toxicon"/>
| .00061–.00157 mg/kg <ref name="Herzig-toxicon"/>
|
|
|-
| Phoneutria
| fera
| [[Brazilian wandering spider]]
| 30 mm <ref name="Vetter"/>
| 1.079 mg <ref name="Herzig-toxicon"/>
| .00061–.00157 mg/kg <ref name="Herzig-toxicon"/>
|
| occasional deaths even after antivenin treatment<ref name="Vetter"/>
|-
| Phoneutria
| nigriventer
| [[Brazilian wandering spider]]
| 3–5 cm (1.25–2 in) <ref name="Petterson">{{cite web|
author=Lelle Petterson|
title=The genus Phoneutria, Perty 1833, wandering spiders|
work=Minax tarantulas|
url=http://www.minaxtarantulas.net/artiklar/phoneutria/phoneutria_e.html
}}</ref>
| 2.15 mg <ref name="Manzoli"/> 1.079 mg. <ref name="Herzig-toxicon"/>
| 15.20 ng/mg <ref name="Manzoli"/> .00061–.00157 mg/kg <ref name="Herzig-toxicon"/>
| 200 µg/kg (0.2 ng/mg) <ref name="Manzoli"/>
|
|-
| Phoneutria
| reidyi
| [[Brazilian wandering spider]]
| 30 mm
|
| .00061–.00157 mg/kg <ref name="Herzig-toxicon"/>
| 0.3 mg/kg
|
|-
| Sicarius
| (Africa & S.A. species)
| [[Six-eyed sand spider]]
| 17 mm
|
|
|
|
|-
| [[Haplopelma]]
| huwenum (previously ''Selenocosmia huwena'')
| [[Chinese bird spider]]
|
|
| 0.70 mg/kg <ref>{{cite journal|
author=Liang SP, Zhang DY, Pan X, Chen Q, Zhou PA|
title=Properties and amino acid sequence of huwentoxin-I, a neurotoxin purified from the venom of the Chinese bird spider Selenocosmia huwena|
journal=Toxicon|
date=1993-08|
volume=31|
issue=8|
pages=969–78|
url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8212049&dopt=Citation|
doi=10.1016/0041-0101(93)90256-I}}</ref>
|
| One infant death reported. <ref name="Spidertalk"> http://www.spidertalk.net/SpiderTalk/post.php?action=reply&fid=1&tid=2165&repquote=16279</ref>
|-
| Poecilotheria
| ornata
| Fringed ornamental tarantula
|
|
|
|
| Instances of coma reported. <ref name="Spidertalk"/>
|-
| Poecilotheria
| fasciata <nowiki>**</nowiki>
| Sri Lankan ornamental tarantula
|
|
|
|
| Instances of cardiac failure reported <ref name="Spidertalk"/>
|-
| Tegenaria
| agrestis
| [[Hobo spider]]
| 7–14 mm <ref name="Vetter"/>
|
|
|
| (1 reported) <ref name="Vetter"/>
|-
| Cheiracanthium
| species
| [[Yellow sac spider]]
| 6–10 mm
|
|
|
| (No severe consequences) <ref name="Vetter"/>
|-
| Cheiracanthium
| japonicum
| Japanese sac
| 6–10 mm
|
|
|
|
|-
| Macrothele
| holsti, gigas, taiwanensis <ref name="THU"/>
| Primitive burrowing spiders
|
|
|
|
| No deaths reported in Taiwan.<ref name="Taiwan"/>
|-
| [[Steatoda]]
| grossa
| [[Steatoda grossa|Cupboard spider]]
|
|
|
|
| Mild widow-like symptoms reported, no severe consequences
|}
<nowiki>*</nowiki> This value is based on experience with human exposures.<br>
<nowiki>**</nowiki> 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.
== Spiders and similar creatures with unsupported reputations ==
There are several species of spider (and a few other [[arachnid]]s 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.
===Hobo spiders (''Tegenaria agrestis'')===
[[Image:Male-hobo.gif|thumb|right|Male Hobo Spider - note the large [[pedipalps]]]]
{{main|Hobo spider}}
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<ref>Vest, D. K. (1987). Envenomation by Tegenaria agrestis (Walckenaer) spiders in rabbits. ''Toxicon'' 25(2):221-4.</ref><ref>Vest, D. K. (1987). Necrotic arachnidism in the northwest United States and its probable relationship to ''Tegenaria agrestis'' (Walckenaer) spiders. ''Toxicon'' 25(2):175-84.</ref>, and medical authorities in the Pacific Northwest have 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 spider]]s have not been found; some of these alleged bites have been attributed to hobo spiders instead.<ref>Vetter, R. S. (2000). Myth: Idiopathic wounds are often due to brown recluse or other spider bites throughout the United States. ''[[Western Journal of Medicine]]'' 173:357-358</ref>
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 methodolgies 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. <ref name="Annemergmed2004-Vetter">{{cite journal | author = Vetter R, Isbister G | title = Do hobo spider bites cause dermonecrotic injuries? | journal = Ann Emerg Med | volume = 44 | issue = 6 | pages = 605–7 | year = 2004 | pmid = 15573036 | doi = 10.1016/j.annemergmed.2004.03.016}}</ref><ref>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.</ref>
===''Lycosa tarantula''===
[[Image:Lycosa Tarantula.jpg|250px|thumb|left|[[Lycosa tarantula]]. Its back is covered with recently hatched spiderlings.]]
''[[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.
===White-tailed spider===
The [[white-tailed spider]], a species indigenous to [[Australia]], has long been blamed for a necrotic bite, producing symptoms similar to a [[brown recluse]]. However, recent studies into this spider have led many to believe that its bite produces no serious effects in humans; in particular, necrotic ulcers were not observed. White-tail bites ''do'' cause localized pain and lesions. <ref name="WhiteTail"/> Nonetheless, the white-tailed spider still is rather infamous in Australia, and frequently referred to as a dangerous spider.
===Harvestman (Daddy-long-legs)===
[[Image:Opiliones harvestman.jpg|thumb|left|Opiliones (harvestman)]]
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 claims that they possess venom which is deadly to humans. This is untrue on several counts. None of the known species have venom glands or fangs, instead having [[chelicerae]].<ref>[http://www.arachnology.be/pages/Opilio_QandA.html Answers to commons questions about harvestmen] - The Arachnology Home Page. Accessed [[2008-04-01]]</ref> In addition, incidents of opiliones biting people are rare, and no reported bites by these species have had any lasting effects.
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.
==="Sun spiders"===
[[Image:Solfuga CM.jpg|thumb|right|Solifugae (sun spider)]]
The arachnids of the order ''[[Solifugae]]'', also known as '''wind scorpions''' or '''sun spiders''', are neither spiders nor [[scorpion]]s. 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.
Further, Solifugae are known to not possess any venom (other than one species in [[India]], which may possess venom according to one study <ref>{{cite journal|
author=Aruchami, M. & G. Sundara Rajulu|
date=1978|
title=An investigation on the poison glands and the nature of the venom of Rhagodes nigrocinctus (Solifugae: Arachnida)|
journal=Nat. Acad. Sci. Letters (India)|
volume=1|
pages=191–192}}</ref>), but do produce, on some occasions, a strong [[anti-coagulant]]{{Fact|date=June 2008}}. Moreover, due to the large size and insanitarity of their jaws, bites by Solifugae can cause significant wounds, which should be treated accordingly to avoid infection from its previous meals.<ref name="CamelSpider"/>
== References==
{{reflist|2}}
== External links ==
*[http://www.scielo.br/scielo.php?pid=S0036-46652000000100003&script=sci_arttext&tlng=en Brazilian article reporting medical research]
*[http://www.mja.com.au/public/issues/182_08_180405/isb10564_fm.html Medical Journal of Australia article gives statistics on the most frequent biters and the most serious bites.]
*[http://www.badspiderbites.com/spider-bite.php Pictures and descriptions of spider bites from around the world.]
*[http://spiders.ucr.edu/dermatol.html Richard S. Vetter and P. Kirk Visscher of the University of California at Riverside]
*[http://www.dbskeptic.com/2008/02/03/spider-bites-are-an-overrated-menace/ Spider bites are an overrated menace]
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