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

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 (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 similar 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.

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. Rarely, the venom is carried by the bloodstream to and cause red blood cell destruction.

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

The Chilean recluse (L. laeta) supposedly has a more potent venom, which results in systemic involvement more often. This spider was introduced to the Los Angeles area (Alhambra, Sierra Madre, and Monterey Park). No verified bites and the subsequent systemic hemolysis have been documented , 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 avoid improper treatment, and to successfully treat common infections or other conditions if no spider was seen.

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.
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 erratic 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, 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 systemic in children, though there has never been a verifiable death as a result of a brown recluse spider bite in North America.
Most bites are unremarkable or mild.

Species

There are about 100 species of Loxosceles.

Species include:

Loxosceles accepta Chamberlin, 1920 — Peru
Loxosceles adelaida Gertsch, 1967 — Brazil
Loxosceles alamosa Gertsch & Ennik, 1983 — Mexico
Loxosceles alicea Gertsch, 1967 — Peru
Loxosceles amazonica Gertsch, 1967 — Brazil
Loxosceles anomala (Mello-Leitão, 1917) — Brazil
Loxosceles apachea Gertsch & Ennik, 1983 — United States, Mexico
Loxosceles aphrasta Wang, 1994 — China
Loxosceles aranea Gertsch, 1973 — Mexico
Loxosceles arizonica Gertsch & Mulaik, 1940 — USA
Loxosceles aurea Gertsch, 1973 — Mexico
Loxosceles baja Gertsch & Ennik, 1983 — Mexico
Loxosceles barbara Gertsch & Ennik, 1983 — Mexico
Loxosceles belli Gertsch, 1973 — Mexico
Loxosceles bettyae Gertsch, 1967 — Peru
Loxosceles blancasi Gertsch, 1967 — Peru
Loxosceles blanda Gertsch & Ennik, 1983 — USA
Loxosceles boneti Gertsch, 1958 — Mexico, El Salvador
Loxosceles candela Gertsch & Ennik, 1983 — Mexico
Loxosceles caribbaea Gertsch, 1958 — Greater Antilles
Loxosceles carmena Gertsch & Ennik, 1983 — Mexico
Loxosceles chinateca Gertsch & Ennik, 1983 — Mexico
Loxosceles colima Gertsch, 1958 — Mexico
Loxosceles conococha Gertsch, 1967 — Peru
Loxosceles coquimbo Gertsch, 1967 — Chile
Loxosceles coyote Gertsch & Ennik, 1983 — Mexico
Loxosceles cubana Gertsch, 1958 — Cuba, Bahama Islands
Loxosceles deserta Gertsch, 1973 — USA, Mexico
Loxosceles devia Gertsch & Mulaik, 1940 — USA, Mexico
Loxosceles fontainei Millot, 1941 — Guinea
Loxosceles foutadjalloni Millot, 1941 — Guinea
Loxosceles francisca Gertsch & Ennik, 1983 — Mexico
Loxosceles frizzelli Gertsch, 1967 — Peru
Loxosceles gaucho Gertsch, 1967 — Brazil, Tunisia
Loxosceles gloria Gertsch, 1967 — Ecuador, Peru
Loxosceles guatemala Gertsch, 1973 — Guatemala
Loxosceles harrietae Gertsch, 1967 — Peru
Loxosceles herreri Gertsch, 1967 — Peru
Loxosceles hirsuta Mello-Leitão, 1931 — Brazil, Paraguay, Argentina
Loxosceles huasteca Gertsch & Ennik, 1983 — Mexico
Loxosceles immodesta (Mello-Leitão, 1917) — Brazil
Loxosceles inca Gertsch, 1967 — Peru
Loxosceles insula Gertsch & Ennik, 1983 — Mexico
Loxosceles intermedia Mello-Leitão, 1934 — Brazil, Argentina
Loxosceles jaca Gertsch & Ennik, 1983 — Mexico
Loxosceles jamaica Gertsch & Ennik, 1983 — Jamaica
Loxosceles jarmila Gertsch & Ennik, 1983 — Jamaica
Loxosceles julia Gertsch, 1967 — Peru
Loxosceles kaiba Gertsch & Ennik, 1983 — USA
Loxosceles lacroixi Millot, 1941 — Ivory Coast
Loxosceles lacta Wang, 1994 — China
Loxosceles laeta (Nicolet, 1849) — South America, introduced to North America, Finland and Australia
Loxosceles lawrencei Caporiacco, 1955 — Venezuela, Trinidad, Curaçao
Loxosceles lutea Keyserling, 1877 — Colombia, Ecuador
Loxosceles luteola Gertsch, 1973 — Mexico
Loxosceles manuela Gertsch & Ennik, 1983 — Mexico
Loxosceles martha Gertsch & Ennik, 1983 — USA
Loxosceles meruensis Tullgren, 1910 — Tanzania
Loxosceles misteca Gertsch, 1958 — Mexico
Loxosceles mulege Gertsch & Ennik, 1983 — Mexico
Loxosceles nahuana Gertsch, 1958 — Mexico
Loxosceles neuvillei Simon, 1909 — Somalia, East Africa
Loxosceles olmea Gertsch, 1967 — Peru
Loxosceles pallidecolorata (Strand, 1906) — Ethiopia
Loxosceles palma Gertsch & Ennik, 1983 — USA, Mexico
Loxosceles panama Gertsch, 1958 — Panama
Loxosceles parrami Newlands, 1981 — South Africa
Loxosceles piura Gertsch, 1967 — Peru
Loxosceles pucara Gertsch, 1967 — Peru
Loxosceles puortoi Martins, Knysak & Bertani, 2002 — Brazil
Loxosceles reclusa Gertsch & Mulaik, 1940 — North America
Loxosceles rica Gertsch & Ennik, 1983 — Costa Rica
Loxosceles rosana Gertsch, 1967 — Peru
Loxosceles rothi Gertsch & Ennik, 1983 — Mexico
Loxosceles rufescens (Dufour, 1820) — Cosmopolitan
Loxosceles rufipes (Lucas, 1834) — Guatemala, Panama, Colombia
Loxosceles russelli Gertsch & Ennik, 1983 — USA
Loxosceles sabina Gertsch & Ennik, 1983 — USA
Loxosceles seri Gertsch & Ennik, 1983 — Mexico
Loxosceles similis Moenkhaus, 1898 — Brazil
Loxosceles smithi Simon, 1897 — Ethiopia
Loxosceles sonora Gertsch & Ennik, 1983 — Mexico
Loxosceles spadicea Simon, 1907 — Peru, Bolivia, Argentina
Loxosceles speluncarum Simon, 1893 — South Africa
Loxosceles spinulosa Purcell, 1904 — Southern Africa
Loxosceles surca Gertsch, 1967 — Peru
Loxosceles taeniopalpis Simon, 1907 — Ecuador
Loxosceles taino Gertsch & Ennik, 1983 — Bahama Islands, Jamaica, Hispaniola
Loxosceles tehuana Gertsch, 1958 — Mexico
Loxosceles tenango Gertsch, 1973 — Mexico
Loxosceles teresa Gertsch & Ennik, 1983 — Mexico
Loxosceles tlacolula Gertsch & Ennik, 1983 — Mexico
Loxosceles unicolor Keyserling, 1887 — South America
Loxosceles valdosa Gertsch, 1973 — Mexico
Loxosceles valida Lawrence, 1964 — South Africa
Loxosceles variegata Simon, 1897 — Paraguay
Loxosceles virgo Gertsch & Ennik, 1983 — Virgin Islands
Loxosceles vonwredei Newlands, 1980 — Namibia
Loxosceles weyrauchi Gertsch, 1967 — Peru
Loxosceles yucatana Chamberlin & Ivie, 1938 — Mexico, Belize, Guatemala
Loxosceles zapoteca Gertsch, 1958 — Mexico

source - Wikipedia
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