''Loxosceles similis'', is a species of a

venomous Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...

recluse spider The recluse spiders (''Loxosceles'' (), also known as brown spiders, fiddle-backs, violin spiders, and reapers, is a genus of spiders that was first described by R. T. Lowe in 1832. They are venomous spiders known for their bite, which sometimes ...

endemic to

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

Description and behavior

Loxosceles similis is not a well-known spider, it is known that two male specimens collected from Brazil, were 5.23 mm and 4.94 mm long and 3.75 mm and 2.96 mm wide respectively, and presented discreet disposition of the overall body color. This species has cave dwelling habits, although it can also occur in homes. Although not very well known, it is possible like other recluse spiders, that this species feeds on small insects, has nocturnal habits and is not aggressive.

Range and habitat

This species occurs in

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

, in

Pará Pará is a Federative units of Brazil, state of Brazil, located in northern Brazil and traversed by the lower Amazon River. It borders the Brazilian states of Amapá, Maranhão, Tocantins (state), Tocantins, Mato Grosso, Amazonas (Brazilian state) ...

Minas Gerais Minas Gerais () is a state in Southeastern Brazil. It ranks as the second most populous, the third by gross domestic product (GDP), and the fourth largest by area in the country. The state's capital and largest city, Belo Horizonte (literally ...

São Paulo São Paulo (, ; Portuguese for 'Saint Paul') is the most populous city in Brazil, and is the capital of the state of São Paulo, the most populous and wealthiest Brazilian state, located in the country's Southeast Region. Listed by the GaWC a ...

Mato Grosso do Sul Mato Grosso do Sul () is one of the Midwestern states of Brazil. Neighboring Brazilian states are (from north clockwise) Mato Grosso, Goiás, Minas Gerais, São Paulo and Paraná. It also borders the countries of Paraguay, to the southwest, and ...

and

Bahia Bahia ( , , ; meaning "bay") is one of the 26 Federative units of Brazil, states of Brazil, located in the Northeast Region, Brazil, Northeast Region of the country. It is the fourth-largest Brazilian state by population (after São Paulo (sta ...

Venom

A recent study on the characterization of the venom of this species showed that its biological effects have an intensity similar to that of ''

Loxosceles laeta The Chilean recluse spider, ''Loxosceles laeta'', is a highly venomous spider of the family Sicariidae. In Spanish, it (and other South American recluse spiders) is known as ', or "corner spider"; in Brazilian Portuguese, as ' or "brown spider". ...

'', ''

Loxosceles intermedia ''Loxosceles intermedia'', the Brazilian brown recluse spider, is a highly venomous spider species in the family Sicariidae native to Brazil and Argentina. Description The male has a total length of 5.3 mm, legs I to IV, have a length of ...

'' and ''

Loxosceles gaucho ''Loxosceles gaucho'' commonly known in English as the gaucho spider. is a highly venomous recluse spider endemic to South America. Description and behavior Adult females grow up to 7–12 mm, the maximum reported is 14 mm. They are ...

'', an experimental study with rabbits injected with 0.5 μg (500 nanograms) of the venom resulted in severe

edema Edema, also spelled oedema, and also known as fluid retention, dropsy, hydropsy and swelling, is the build-up of fluid in the body's Tissue (biology), tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels t ...

, diffuse heterophilic inflammatory infiltrate, perivascular heterophilic infiltrate,

thrombosis Thrombosis (from Ancient Greek "clotting") is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel (a vein or an artery) is injured, the body uses platelets (thro ...

in all layers of the

dermis The dermis or corium is a layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. It is divided i ...

fibrinoid necrosis Fibrinoid necrosis is a specific pattern of irreversible, uncontrolled cell death that occurs when antigen-antibody complexes are deposited in the walls of blood vessels along with fibrin. It is common in the immune-mediated vasculitides which ar ...

of the arteriolar wall, cutaneous muscle necrosis and dermal

hemorrhage Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, vag ...

. It is concluded that ''L. similis'' venom induces

apoptosis Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes incl ...

endothelial cells The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel ...

. The minimum, average and maximum amount of venom produced by ''L. similis'' is 0.10 mg, 0.70 mg and 1.5 mg respectively.

References

{{Taxonbar, from=Q2597144 Spiders of South America Fauna of Brazil Sicariidae Spiders described in 1898