Recluse spider

Recluse spider
Loxosceles gaucho from 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 venomous genus of spiders known for their necrotic 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, "Loxoscelidae."

Contents

Habitat and appearance

Loxosceles is distributed nearly worldwide in warmer areas, and are often known as violin spiders, fiddlebacks or reapers. 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 literally 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.

The recluse spider family includes about 13 species in the United States, the brown recluse spider (Loxosceles reclusa) being the best known of these. 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 (L. laeta) and the Mediterranean recluse (Loxosceles rufescens).

Recently, concerns have been raised regarding recluses spreading faster due to warmer air carrying them farther as a result of global warming. 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

Loxosceles spiders, like their cousins in Sicarius, 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] This venom is highly necrotic in effect, capable of causing lesions (open sores) as large as a bottle cap. The wounds take a long time to heal and may require skin grafts. If these open wounds become infected there are often serious consequences. Rarely, the venom is carried by the blood stream to internal organs causing systemic effects.

The constituency of recluse venom is identical in both male and female spiders, although females have a particularly potent venom, containing up to 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 (Loxosceles 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 lived there for over 30 years. Other members of the genus that have been tested have venoms similar to the brown recluse and all members of this genus are best avoided. However, the brown recluse and its relatives are not very aggressive and huge populations have been found in houses where the human inhabitants remained unbitten after years of cohabitation.[5]

A possible problem with diagnosing a recluse spider bite is that the bite of these spiders is probably both underreported in some areas and over reported generally.[6] Unfortunately several diseases can mimic the lesions of a recluse spider bite, including Lyme disease, various fungal and bacterial infections and the first sore of syphilis.[7] Therefore it is extremely important to associate the spider directly with the bite, if at all possible, and consider alternative diagnoses if no spider was seen.

Recluse spiders are usually found in the center of space webs made of fungus-like silk, which often contains the remains of their recent meals. The most abundant food items for the Arizona recluse (Loxosceles arizonica) are night-active ants such as carpenter ants. The brown recluse feeds on whatever small prey is available. This is also true of all sicariids. Loxosceles reclusa have been shown in laboratory experiments to prefer scavenging than actively hunting.[8]

Bites most often occur when the spider is engaging in defense while trapped against the skin, such as when the person is putting on clothes the recluse is inside of, or when the person while sleeping rolls over against the recluse.[1] However, bug spray and other chemicals intended to repel or kill arthropods that do not kill the recluse will cause its nervous system to break down partially, inducing undesirable aggressive behavior.[9]

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

Species

See also

Footnotes

  1. ^ a b c d e R. S. Vetter (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. http://www.americanarachnology.org/JoA_free/JoA_v36_n1/arac-36-1-150.pdf. 
  2. ^ Binford G.J. et al (2005). "Sphingomyelinase D from venoms of Loxosceles spiders: evolutionary insights from cDNA sequences and gene structure". Toxicon 40: 547–560. http://legacy.lclark.edu/~binford/Binfordetal2005.pdf. 
  3. ^ Schroeder, F.C., Taggi, A.E., Gronquist, M., Malik, R.U., Grant, J.B., Eisner, T., & Meinwald, J. (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, David L.; Vetter, Richard S. (2006). "Loxoscelism". Clinics in Dermatology 24 (3): 213–221. doi:10.1016/j.clindermatol.2005.11.006. PMID 16714202. http://urban.cmsdev.ucr.edu/docs/Spiders/%20Loxoscelism_S&V.pdf. Retrieved 12 April 2011. 
  5. ^ Vetter R, Barger D (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, Bush S (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. doi:10.1038/426030a. PMID 14603305. 
  9. ^ Hite, J.M. (1966). The biology of the brown recluse spider. Kansas State University. 
  10. ^ Wright, S.W., Wrenn, K.D., Murray, L., & Seger, D. (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. 
  11. ^ Anderson, P.C. (1998). "Missouri brown recluse spider: a review and update". Missouri Medicine 95: 318–22. 
  12. ^ Cacy, J. & Mold, J.W. (1999). "The clinical characteristics of brown recluse spider bites treated by family physicians: an OKPRN study". Journal of Family Practice 48: 536–42. 
  13. ^ Pauli, I., Puka, J., Gubert, I.C., & Minozzo, J.C. (2006). "The efficacy of antivenom in loxoscelism treatment". Toxicon 48 (2): 123–37. doi:10.1016/j.toxicon.2006.05.005. 

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