Recluse spider

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Recluse spider
LoxoscelesGaucho.jpg
Loxosceles gaucho, Brazil
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Arachnida
Order: Araneae
Family: Sicariidae
Genus: Loxosceles
Heineken & Lowe, 1832
Species

see article

Diversity
100 species

The recluse spiders or brown spiders (genus Loxosceles), 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[edit]

Sicariidae are of the superfamily Scytodoidea. Other families in the Scytodoidea include Drymusidae, Scytodidae, and Periegopidae.

Habitat and appearance[edit]

Loxosceles is distributed nearly worldwide in warmer areas. All have six eyes arranged in three groups of two (dyads) 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 (Loxosceles reclusa). 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 (L. laeta) and the Mediterranean recluse spider (L. rufescens).

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.[1]

Venom components and effects[edit]

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.[2] 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.[3] 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.[4] 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.[4]

The Chilean recluse (L. laeta) supposedly has a more potent venom, which results in systemic involvement more often. This spider was accidentally introduced to the Los Angeles area (Alhambra, Sierra Madre, and Monterey Park). 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.[5]

Many types of skin wounds are mistaken for or assumed to be the result of a recluse spider bite.[6] Several diseases can mimic the lesions of the bite, including Lyme disease, various fungal and bacterial infections, and the first sore of syphilis.[7] 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 (L. arizonica) 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.[8]

Bites most often occur as a defense when the spider is trapped against the skin, in clothing, for example.[1] Insecticides often fail to kill the spider, instead intoxicating its nervous system and inducing aggressive behavior.[9]

The bite of a recluse spider can generally be categorized into one of the following groups:[1]

  • 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.[10] In extreme cases, the lesion may be up to 40 centimeters wide, last for several months, and heal with a permanent scar.[1]
  • 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.[1]

Most bites are unremarkable or mild.[11][12][13]

Species[edit]

There are about 100 species of Loxosceles.[1]

Species include:

See also[edit]

Footnotes[edit]

  1. ^ a b c d e f Vetter, R. S. (2008). "Spiders of the genus Loxosceles: a review of biological, medical and psychological aspects regarding envenomations" (PDF). Journal of Arachnology 36 (3): 150–163. doi:10.1636/RSt08-06.1. 
  2. ^ Binford, G. J. et al. (2005). "Sphingomyelinase D from venoms of Loxosceles spiders: evolutionary insights from cDNA sequences and gene structure". Toxicon 40 (5): 547–560. doi:10.1016/j.toxicon.2004.11.011. PMID 15777950. 
  3. ^ Schroeder, F. C., et al. (2008). "NMR-spectroscopic screening of spider venom reveals sulfated nucleosides as major components for the brown recluse and related species". PNAS 105 (38): 14283–14287. Bibcode:2008PNAS..10514283S. doi:10.1073/pnas.0806840105. 
  4. ^ a b Swanson, D. L.; Vetter, R. S. (2006). "Loxoscelism". Clinics in Dermatology 24 (3): 213–221. doi:10.1016/j.clindermatol.2005.11.006. PMID 16714202. Retrieved 12 April 2011. 
  5. ^ Vetter, R. and D. Barger. (2002). "An infestation of 2,055 brown recluse spiders (Araneae: Sicariidae) and no envenomations in a Kansas home: implications for bite diagnoses in nonendemic areas". J Med Entomol 39 (6): 948–51. doi:10.1603/0022-2585-39.6.948. PMID 12495200. 
  6. ^ Vetter, R. and S. Bush. (2002). "The diagnosis of brown recluse spider bite is overused for dermonecrotic wounds of uncertain etiology". Ann Emerg Med 39 (5): 544–6. doi:10.1067/mem.2002.123594. PMID 11973562. 
  7. ^ http://spiders.ucr.edu/necrotic.html
  8. ^ Sandidge, J. (2003). "Arachnology: Scavenging by brown recluse spiders". Nature 426 (30): 30. Bibcode:2003Natur.426...30S. doi:10.1038/426030a. PMID 14603305. 
  9. ^ Hite, J. M. (1966). The biology of the brown recluse spider. Kansas State University. 
  10. ^ Pauli, I., et al. (2006). "The efficacy of antivenom in loxoscelism treatment". Toxicon 48 (2): 123–37. doi:10.1016/j.toxicon.2006.05.005. 
  11. ^ Wright, S. W., et al. (1997). "Clinical presentation and outcome of brown recluse spider bite". Annals of Emergency Medicine 30: 28–32. doi:10.1016/S0196-0644(97)70106-9. 
  12. ^ Anderson, P. C. (1998). "Missouri brown recluse spider: a review and update". Missouri Medicine 95 (7): 318–22. PMID 9666677. 
  13. ^ Cacy, J. and J. W. Mold. (1999). "The clinical characteristics of brown recluse spider bites treated by family physicians: an OKPRN study". Journal of Family Practice 48 (7): 536–42. PMID 10428252. 

External links[edit]