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Comprehensive Description

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The spider family Sicariidae includes 132 described species placed in two genera, Loxosceles and Sicarius (Platnick 2014).Loxosceles species, which account for most of the sicariids, are found in the Mediterranean region, northern Africa, and South and Central America; Sicarius includes just around two dozen described species, which are found in Africa and South and Central America. (Platnick 2014) Thirteen sicariids (all Loxosceles) are known from North America north of Mexico (Ubick 2005).

Sicariids are among the minority of spiders with six eyes. This family includes several well known spiders whose bites are medically significant for humans, such as the Brown Recluse (L. reclusa) in North America, L. boneti in Mexico (Ramos-Cerrillo et al. 2004), and L. intermedia, among others, in South America (Fischer and Vasconcellos-Neto 2005 and references therein).

The genus Loxosceles has a worldwide distribution. In North America north of Mexico, most species are restricted to the southwest, from southern California to southern Texas. The Brown recluse has a wide natural distribution along the Mississippi Basin and adjacent parts of the southcentral United States (future climate change may result in a northward expansion of this distribution; Saupe et al. 2011), but has spread synanthropically to isolated localities outside this region. (Ubick 2005)Loxosceles laeta is a South American species now known from a few localities along both coasts of North America, including southwestern Canada (as well as Finland and Australia) (Gertsch and Ennik 1983)The Mediterranean Recluse (L. rufescens) is native to the Mediterranean region; it has been inadvertently transported by humans around the world, but is typically restricted to local (sometimes dense) populations in particular buildings. Loxosceles rufescens is now established over much of the southern United States and in New York (as well as much of the rest of the world). Although L. rufescens is frequently found outdoors in all but the northernmost parts of its Old World range, all confirmed North American collections have so far been from inside structures, mostly institutional (e.g. governmental, academic, museums) or commercial rather than smaller residential buildings. Greene et al. (2009) reported on L. rufescens populations in a number ofbuildings in Washington, D.C. Unlike L. reclusa, D.C. populations of L. rufescens are essentially troglophilic, concentrated mainly in basements, foundation walls, and other man-made subterranean habitats, typically in close association with American Cockroaches (Periplaneta americana) and/or Reticulitermes termites. (Greene et al. (2009)

Loxosceles are found in a range of habitats from deserts to mesic habitats and, as noted above, some species are often synanthropic. They are typically hidden in crevices they line with silk and extend beyond their retreat. The silk is sticky, readily capturing prey, and somewhat resembles cribellate silk although it is structurally different (Stern and Kullmann 1981 cited in Ubick 2005). Studies on the biology of L. reclusa indicate that it is a generalist feeder with a univoltine life cycle (i.e., with a single generation per year), but may live up to three years in captivity (Hite et al. 1966 cited in Ubick 2005). Observations on the biology of Loxosceles deserta (discussed as Locosceles unicolor) were presented by Ennik (1971 cited in Ubick 2005) and on L. arizonica by Richman (1973).

Although Loxosceles spiders are widely perceived to be a major public health menace, at least in the case of L. reclusa in the United States it is clear that many supposed cases of Loxosceles bites actually have other causes. In fact, Brown Recluses are often blamed for supposed bites in areas where the best available data indicate they are not even present (Vetter et al. 2003; Vetter 2005, 2008; Vetter and Isbister 2008) or at times of the year when bites are unlikely (Vetter 2011). Such misdiagnoses do not merely endanger the reputation of L. reclusa, but more importantly, they can endanger human patients who are often actually suffering from potentially more dangerous dermatologic conditions such as MRSA infections (e.g., Moran et al. 2006). A similar situation has been described in Australia, with necrotic ulcers being routinely attributed to spider bites on very weak evidence (Isbister 2001 but see Young and Pincus 2001; Swanson and Vetter 2005).

In the southcentral United States, however, Brown Recluses can, in fact, be very abundant in houses (Sandidge and Hopwood 2005) and a bite can be a serious medical event. Loxosceles reclusa venom is potent and can produce lesions and persistent sores in humans, although rarely death (Gertsch and Ennik 1983). In South America, Loxosceles species present a far greater public health issue, although here, also, these spiders are likely blamed for significantly more medical events than they are actually resposible for. Although Loxosceles venom can do serious damage to vertebrates, its primary evolved function is believed to be to immobilize insect prey (Zobel-Thropp et al. 2012).

The Nearctic and Neotropical Loxosceles have been revised by Gertsch and colleagues (Gertsch and Mulaik 1940; Gertsch 1958; Gertsch 1967; Gertsch 1973; Gertsch and Ennik 1983). Loxosceles and Sicarius were at one time placed in their own families (Loxoscelidae and Sicariidae) and have also been included in the Scytodidae, another family of six-eyed spiders. (Ubick 2005)Binford et al. (2008) and Duncan et al. (2010) investigated the phylogenetic and phylogeographic relationships within Loxosceles and Sicarius.

(Ubick 2005; Bradley 2013)

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Sicariidae

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Sicariidae is a family of six-eyed venomous spiders known for their potentially necrotic bites. The family consists of three genera and about 160 species. Well known spiders in this family include the brown recluse spider and the six-eyed sand spider.

Description

Loxosceles, commonly known as "recluse spiders" or "violin spiders", is distributed nearly worldwide in warmer areas. Hexophthalma and Sicarius, commonly known as "sand spiders" or "assassin spiders", live in the deserts of southern Africa and South to Central America, respectively.[1] They are known for their self-burying behavior and the ability to go for long periods without food or water.[2]

All members have six eyes arranged in three groups of two (dyads). Violin spiders are usually brownish with a darker brown characteristic violin marking on the cephalothorax. They are also haplogyne, meaning the females possessing unsclerotised genitals.[3]

Hexophthalma and Sicarius resemble crab spiders and lack this marking. With the tarantulas, these are some of the longest living spiders, some living up to fifteen years old. Most Loxosceles can live for one and a half to two years.

Venom

All genera are able to produce sphingomyelinase D or a related tissue-destroying substance. It is unique to the family among spiders, and otherwise only found in a few pathogenic bacteria. Bites from most of the Neotropical species of Sicarius are not known to display dermonecrotic or systemic activity, except the highly venomous Sicarius ornatus which has active proteins of the sphingomyelinase D family found in the venom.[4][5]

The venom of many Sicariidae species is highly hemolytic and dermonecrotic,[2] capable of destroying red blood cells and causing lesions as large as 1 inch (25 mm) in diameter that take a long time to heal. Some require skin grafts and if the open wound gets infected, there can be even more serious consequences. Rarely, the venom is carried by the blood stream into internal organs causing systemic effects. Unlike spiders that use neurotoxins, many of the venoms used by these spiders do not have a known anti-venom.[2]

Taxonomy

The family was first described by Eugen von Keyserling in 1880,[3] and marked as a subfamily and synonym for "Loxoscelidae" in 1893.[6] The status of "Loxoscelidae" as a family or subfamily of "Sicariidae" has been argued both ways. The World Spider Catalog currently accepts Loxoscelinae as a subfamily of Sicariidae,[7] but this placement is still being debated.[8][9]

A phylogenetic study in 2017 showed that the African species of Sicarius were distinct, and placed them in the revived genus Hexophthalma. The relationship found between the genera is shown in the following cladogram:[5]

Sicariidae Loxoscelinae

Loxosceles

  Sicariinae  

Hexophthalma

   

Sicarius

     

Genera

As of March 2019, the World Spider Catalog accepts the following genera:[1]

  • Hexophthalma Karsch, 1879 – Namibia, South Africa
  • Loxosceles Heineken & Lowe, 1832 – South America, North America, Asia, Africa, Central America, Caribbean, Finland, Australia
  • Sicarius Walckenaer, 1847 – South America, Central America

See also

References

  1. ^ a b c "Family: Sicariidae Keyserling, 1880". World Spider Catalog. Natural History Museum Bern. Retrieved 2019-04-27.
  2. ^ a b c "Six Eyed Sand Spider". Animal Corner. Retrieved 2019-04-24.
  3. ^ a b Keyserling, E. (1880). Die Spinnen Amerikas, I. Laterigradae.
  4. ^ Binford, Greta J.; Wells, Michael A. (2003). "The phylogenetic distribution of sphingomyelinase D activity in venoms of Haplogyne spiders" (PDF). Comparative Biochemistry and Physiology B. 135: 25–33. doi:10.1016/s1096-4959(03)00045-9.
  5. ^ a b Magalhães, I.L.F.; Brescovit, A.D. & Santos, A.J. (2017). "Phylogeny of Sicariidae spiders (Araneae: Haplogynae), with a monograph on Neotropical Sicarius". Zoological Journal of the Linnean Society. 179 (4): 767–864. doi:10.1111/zoj.12442.
  6. ^ Simon, E. (1893). Histoire naturelle das araignées. p. 271.
  7. ^ Platnick, N. I.; Coddington, J. A.; Forster, R. R.; Griswold, C. E. (1991). "Spinneret morphology and the phylogeny of haplogyne spiders (Araneae, Araneomorphae)". American Museum Novitates. 3016.
  8. ^ Murphy, J. A.; Roberts, M. J. (2015). Spider families of the world and their spinnerets. British Arachnological Society, York.
  9. ^ Wunderlich, J. (2004). "Fossil spiders (Araneae) of the superfamily Dysderoidea in Baltic and Dominican amber, with revised family diagnoses". Beiträge zur Araneologie. 3: 633–746.

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Sicariidae: Brief Summary

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Sicariidae is a family of six-eyed venomous spiders known for their potentially necrotic bites. The family consists of three genera and about 160 species. Well known spiders in this family include the brown recluse spider and the six-eyed sand spider.

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