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  • The recluse spiders or brown spiders, also known as fiddle-back, violin

  • spiders or reapers, are a genus of venomous spiders known for their bite,

  • which sometimes produces a characteristic set of symptoms known as

  • loxoscelism. Recluse spiders are now identified as members of the family

  • Sicariidae, having formerly been placed in their own family, the Loxoscelidae.

  • Relation to other spiders Sicariidae are of the superfamily

  • Scytodoidea. Other families in the Scytodoidea include Drymusidae,

  • Scytodidae, and Periegopidae. Habitat and appearance

  • Loxosceles is distributed nearly worldwide in warmer areas. All have six

  • eyes arranged in three groups of two and some are brownish with a darker brown

  • characteristic violin marking on the cephalothorax. However, the "violin

  • marking" cannot be used as a reliable way to identify the spider as thousands

  • of species of spider have the same markings. Spiders come with many

  • markings varying greatly within the same species. Most Loxosceles can live for

  • one and a half to two years. Members of both genera can live for very long times

  • without food or water. They are about 7–12 mm long.

  • Familiar species in the United States include the brown recluse spider. It is

  • found in a large area of the Midwest, west to Colorado and the New Mexico

  • state line and east to northern Georgia. Sporadic records from other locations

  • only represent incidental introductions, not established populations. Other

  • notable members of this genus include the Chilean recluse spider and the

  • Mediterranean recluse spider. Recently, concerns have been raised

  • regarding recluses spreading faster due to warmer air carrying them farther as a

  • result of changing climate. On the contrary, newly hatched recluses do not

  • travel via ballooning and thus the populations are confined to very tight

  • spaces with dense populations. Venom components and effects

  • Loxosceles spiders, like Sicarius species, have potent tissue-destroying

  • venoms containing the dermonecrotic agent, sphingomyelinase D, which is

  • otherwise found only in a few pathogenic bacteria. Recent research has indicated

  • the venom is composed largely of sulfated nucleosides, though these

  • compounds are relatively new discoveries, so little is known about

  • them. The venom produces necrotic lesions that are slow to heal and may

  • require skin grafts. The wounds are also prone to infection. Rarely, the venom is

  • carried by the bloodstream to internal organs, causing systemic effects.

  • The venom is identical in male and female spiders, but females can have

  • almost twice the concentration of toxins. For unknown reasons, the

  • toxicity of the venom to mammalian species varies; recluse bites will cause

  • necrosis in humans, rabbits, and guinea pigs, but not in mice or rats.

  • The Chilean recluse supposedly has a more potent venom, which results in

  • systemic involvement more often. This spider was accidentally introduced to

  • the Los Angeles area. This spider, however, seems to be confined to a very

  • limited area, even though it has been known there for over 30 years. All

  • Loxosceles species that have been tested have venoms similar to that of the brown

  • recluse and all should be avoided. In general, though, they are not aggressive

  • and commonly occupy human dwellings without causing problems.

  • Many types of skin wounds are mistaken for or assumed to be the result of a

  • recluse spider bite. Several diseases can mimic the lesions of the bite,

  • including Lyme disease, various fungal and bacterial infections, and the first

  • sore of syphilis. It is important to associate the spider directly with the

  • bite to initiate proper treatment, and to consider alternative diagnoses if no

  • spider was seen. A recluse spider is usually found in the

  • center of its web, which often contains the remnants of prey items. The most

  • common food items for the Arizona recluse are night-active ants such as

  • carpenter ants. The brown recluse feeds on whatever small prey is available, and

  • has been observed to prefer scavenging over actively hunting.

  • Bites most often occur as a defense when the spider is trapped against the skin,

  • in clothing, for example. Insecticides often fail to kill the spider, instead

  • intoxicating its nervous system and inducing aggressive behavior.

  • The bite of a recluse spider can generally be categorized into one of the

  • following groups: Unremarkable - self-healing minute

  • damage Mild reaction - self-healing damage with

  • itchiness, redness, patterns of aggressive behavior and a mild lesion.

  • Dermonecrotic - the uncommon, "classic" recluse bite, producing a necrotic skin

  • lesion. About 66% of necrotic bite lesions heal with no complications. In

  • extreme cases, the lesion may be up to 40 centimeters wide, last for several

  • months, and heal with a permanent scar. Systemic or viscerocutaneous - an

  • extremely rare, sometimes fatal systemic reaction to envenomation of the

  • bloodstream. This reaction is more common in obese victims, because the

  • venom destroys adipose tissue. It is more often fatal in children.

  • Most bites are unremarkable or mild. Species

  • There are about 100 species of Loxosceles.

  • Species include: See also

  • List of Sicariidae species Spider families

  • List of spiders associated with cutaneous reactions

  • Chilean recluse Footnotes

  • External links Arachnology Home Pages: Loxosceles:

  • Recluse spiders Biodiversity Explorer: Family

  • Sicariidae. World Spider Catalog. 2014.

  • Vetter, R. 2003. Causes of Necrotic Wounds other than Brown Recluse Spider

  • Bites. Vetter, R. 2003. Myth of the Brown

  • Recluse Fact, Fear, and Loathing. Pictures of L. reclusa and wound

The recluse spiders or brown spiders, also known as fiddle-back, violin

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B2 H-INT US recluse spider venom bite brown systemic

Recluse spider

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    James Lin   posted on 2016/02/26
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