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Spider bite

    '''Spiders having medically significant venom''' exist in almost all all 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
    Most spiders are unlikely to bite humans because they do not identify humans as prey Spiders even small ones may however bite humans when pinched For instance a common jumping spider (Family: Salticidae) around 3/8 inch (1 cm) long when pinched between the folds of a human's palm may inflict a bite that is about as painful as a bee sting
    Dangerous spiders in the United States include widow spiders brown spider]s hobo spiders and yellow sac spiders
    None of these spiders will intentionally "come after you" but they should be removed from one's house to avoid accidental injury Many authorities warn against spraying poisons indiscriminately to kill all spiders because doing so may actually remove one of the biological controls against incursions of the more dangerous species by ridding them of their competition
    If dangerous spiders are present in your area be mindful when you move cardboard boxes and other such objects that may have become the shelter of a poisonous spider There is no need to be fearful; just do not grab a spider

    Key to bite severity

    The following key is used in this article as a rough indicator of bite severity:
    • Extremely dangerous: Bite (assuming successful envenomation) may cause death in healthy adults should they not receive emergency medical treatment
    • Very dangerous: Bite may cause death or debilitating injury in children the elderly and the infirm providing that they do not receive prompt medical treatment
    • Dangerous: Bite that are unlikely to cause death (generally few or no deaths have been reported); bites may cause significant local or systematic reactions Medical attention is generally required to limit the scope of symptoms
    • Painful bites: Venom may inflict localized pain (similar to a bee sting) but does not have any dangerous or long-term side effects Medical attention is generally not required
    • Not dangerous: The spider is unable to puncture human skin and/or its venom does not cause any significant reaction in humans
    • No venom: Some species do not produce any venom The only true family of spiders in this category is the hackled orb-weavers; other arachnids often confused with spiders such as the harvestman also do not produce venom

    Types of spiders with medically significant venom

    The following types of spiders are known to have medically significant bites with symptoms ranging from localized pain all the way to severe tissue destruction and potential death

    Brazilian wandering spiders (extremely dangerous)

    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 It, like several other more harmless spiders may hitch a ride in clusters of bananas 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 dry bites and no venom is released The spiders are as large as some small tarantulas and 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-1980's and the wandering spider in 1996) no humans have died from their bites 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 these two types of spiders may be expected

    Australian venomous funnel-web spiders (extremely dangerous)

    Atrax robustus Sydney Funnel-web Spider
    The Australian venomous 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 often delivers dry bites these spiders typically deliver a full envenomation when they biteThere 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

    Six eyed sand spiders (believed to be very dangerous)

    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 recognize 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

    Widow spiders (very dangerous)

    The widow spiders (genus Latrodectus) such as the black widow and red-back spider are spiders that carry a neurotoxic venom Like many spiders widows have very poor vision (jumping spiders and wolf spiders being notable exceptions) 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

    Brown recluse spiders (very dangerous)

    (photo courtesy of the University of Nebraska-Lincoln)Brown spider]s (also known as "violin spiders" or "fiddlers" from the dark violin-shaped marking on the cephalothorax) Loxosceles reclusa 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 Brown recluses are extremely poisonous Most encounters with this spider occur from moving boxes or rooting about in closets or under beds The range of this spider in the US is approximately the lower 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
    Brown recluse spider bites can produce very severe local symptoms death of tissue around the wound and sometimes severe systemic symptoms including organ damage The bites of hobo spiders and yellow sac spiders can cause both pain and necrosis (tissue death) Typically all these bites are characterized by open sore-like wounds that heal very slowly and may leave scarring It has been suggested that steroid treatments may speed healing and reduce scarring
    There are other species of spider in the genus Loxosceles which are found in southern California and other southwestern states; most of these species live in remote areas and are rarely encountered by humans Bites of Loxosceles spiders found in South America are more serious in their consequences than their North American relatives

    Hobo spiders (dangerous)

    The hobo spider Tegenaria agrestis may wander away from its web especially in the fall and thus come into contact with people and bite This spider is found in the northwestern United States and throughout much of Europe Oddly enough in Europe it is considered a harmless outdoor relative of the common house spider (Tegenaria domestica)
    It is believed that many spider bites which are attributed (often by physicians and other medical personnel) to the brown recluse are in fact caused by the hobo spider (if caused by a spider at all) Many brown recluse bites are reported in the US west coast states (Washington Oregon and northern California) where populations of brown spider]s have not been found

    Yellow sac spiders (painful bites)

    (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 "cob-webs" that are removed with broom and vacuum cleaner People may unintentionally make contact with them in the dark and so be bitten However most people will live their entire lives in close proximity to them and never suffer a bite

    Huntsman spiders (painful bites)

    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 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 (painful bites)

    Some people have reported being bitten by redback jumping spiders (Phidippus johnsoni) Many reports come from Californiaalthough 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
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  • Author
    Bjenks
    2009--06-