Loxosceles It is a genus of spiders of the family Sicariidae of medium size, generally between 5 and 13 mm in length, with a pyriform cephalothorax. They have two pairs of lateral eyes and one pair located anteriorly, distributed in the shape of a triangle. The anterior or frontal eyes are larger than the lateral eyes.
The spiders of this genus are known by the name of violinist spiders because they generally have marks on the thorax in the shape of said musical instrument. They are also called corner spiders, because they tend to live hidden in corners and crevices that are difficult to access..
The genus is represented by more than 100 species of wandering spiders distributed worldwide. The greatest diversity of species is found in Latin America, especially in Mexico (41 species) and Peru (19 species). Depending on the species, the preferred habitat can vary from temperate forests to deserts or dunes.
Fiddler spiders are part of a small group of spiders whose venom can kill humans. Along with black widows (genus Latrodectus) are the largest and most dangerous responsible for poisoning by spiders worldwide. Its venom is proteolytic and necrotoxic and produces a series of symptoms known as loxoscelism..
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Spiders of the genus Loxosceles They are medium-sized organisms, generally not exceeding 15 mm long, with larger females and a more developed abdomen (opistosoma).
The prosoma or cephalothorax is pyriform, ornamented with a series of violin-shaped spots. In the anterior part there are six eyes arranged in three pairs in recurrent transverse rows, the anterior pair larger than the rest and located frontally.
The prosoma or cephalothorax is pyriform, ornamented with a series of violin-shaped spots. In the anterior part of it there are six eyes arranged in dyads, the anterior pair is larger than the others and is located frontally, while the remaining two pairs are located laterally..
The chelicerae or buccal appendages are united on their inner margin by a membrane up to half their length. The lamina where these appendages articulate (cheliceral lamina) presents the bifid apex.
It has two tarsal claws armed with a single row of teeth, in females the pedipalp lacks claws. The relative size of the legs varies by species, but the third pair is always the shortest.
The larger bullous glands have a slit-shaped opening, the posterior median rows (spinerettes) lack a spit, while the posterior lateral ones have modified setae..
Females lack external sexual organs, that is, they are haplogins and present a wide gonopore surrounded by mushrooms that leads internally to two storage receptacles. The male copulatory organ is represented by a simple bulb and a plunger with a thin tube without accessory structures..
Spiders of this genus have nocturnal habits and their degree of activity is closely related to the ambient temperature; its presence is accentuated in the warmer months.
Fiddler spiders are taxonomically located in the order Araneae, suborder Araneomorphae, family Sicariidae. In this family, until recent years, taxonomists only recognized two genera, Loxoscheles Y Sicarius, although currently some authors have resurrected the genre Hexophthalma, proposed by Karsch in 1879.
The gender Loxoscheles It was erected by Heineken and Lowe in 1832 and currently consists of 116 species, most of which are present in the Neotropic regions.
Both the family Sicariidae and the genus Loxoscheles have been shown to be monophyletic, however, some authors suggest that the species L. simillima could belong to a new genus not yet described.
In natural environments, the species of Loxoscheles they occupy a great diversity of habitats. They can be found in temperate forests, rain forests, savannas, chaparral, and deserts. They prefer dark places such as leaf litter, under decaying logs, in hollows of trees or in pieces of bark.
Some species are synanthropic, that is, they have adapted very well to environments modified by man, being able to live in houses or in peridomiciliary environments. Inside the houses they can live in attics, under furniture, behind pictures or in any corner or crevice that is difficult to access..
The gender Loxoscheles It is globally distributed, with a greater number of species described in the Neotropics (87 species). The greatest diversity has been reported for Mexico with 41 species.
At least 23 species are known to inhabit the Arctic regions (13 in the Nearctic and 10 in the Palearctic), while only two species are considered cosmopolitan..
Fiddler spiders are mainly insectivorous carnivorous animals. These spiders build webs whose short hammock shape is not very efficient for capturing their prey, but their sticky condition and resistance allow them to trap some organisms..
They are also active hunters, mainly during night hours. When they capture a prey, they quickly inoculate it with the poison and after its death they inject digestive juices that dissolve the tissues of the prey..
After digestive juices digest the prey, the spider sucks in the nutrients and continues digestion inside its body..
Spiders of the genus Loxoscheles they are all dioecious (they present separate sexes), with sexual dimorphism in terms of size, with females larger than males. Fertilization is internal and the eggs develop in ootheca.
Before mating there is a courtship, in which the male jumps and dances around the female and sometimes gives her a prey as an offering. If the male is accepted, the female raises the cephalothorax and the male introduces the pedipalps (which have been modified as secondary copulatory organs) into the female's gonopore..
Sperm are released in packages called spermatophores and deposited in receptacles in the female (spermatheca). The female releases the eggs and these are fertilized by the sperm. Once the ovules are fertilized, the female places a variable number of eggs, depending on the species, in an ootheca.
Each female can produce several ootheca in each reproductive period. Eggs take between 30 and 60 days to hatch, depending on the species and incubation temperature.
The poison of Loxosceles It is complex in composition, in which many components are involved, including: sphingomyelinases, metalloproteinases, alkaline phosphatase and serine proteases.
It is essentially proteolytic and necrotic in action and produces a series of effects that together are called loxoscelism. Loxoscelism can be cutaneous, affecting skin cells and tissues; or visceral or systemic, in which the venom enters the bloodstream and is transported to different organs of the body.
Sphingomyelinase D is the main responsible for necrosis, as well as hemolysis caused by this poison.
When the venom penetrates the tissues, it causes an inflammatory reaction involving arachidonic acid and prostaglandins, which causes severe vasculitis. With occlusion of the local microcirculation, hemolysis, thrombocytopenia, and disseminated intravascular coagulation (DIC) can also occur..
Loxoscelism can also include tissue necrosis, coagulation, and kidney failure. Although there is a specific treatment against loxoscelism, the antidote is only effective when given in the first hours after the bite. Otherwise it loses effectiveness until it becomes completely ineffective.
Other treatments include the application of ice, immobilization of the affected limb, pain relievers, application of oxygen at high pressures or electrical current, colchicine, antihistamines, corticosteroids and dapsone, all of them with contradictory results..
It is native to South America, common in Chile, Peru, Ecuador, Argentina, Uruguay, Paraguay, and Brazil. It has been accidentally introduced in different countries of North America and Central America, as well as in Australia, Finland and Spain.
It is one of the species of Loxosceles larger (up to 15 mm) and wider (or robust) than their congeners from other species. It is one of the most dangerous fiddler spiders due to the power of its venom and it is also the species with the largest distribution in the American continent..
Anaphylactic shock can occur between 5% and 20% of cases, with mortality occurring in about 1/3 of these cases..
It is a species native to the Mediterranean area of the European continent, although it has been accidentally introduced in various countries of the Asian continent, as well as in Australia, Madagascar and North America. It is also present in some islands of the Pacific and the Atlantic.
One of the characteristics of Loxosceles rufescens It is the presence of a large cardiac spot, although sometimes inconspicuous. Its coloration ranges from brown to light reddish, tending to be slightly lighter than other species of the genus..
This species, which can reach 20 mm, is the most poisonous spider in the Mediterranean area and is very prolific, as it can lay up to 300 eggs in a single ootheca..
It is endemic to North America and is widely distributed in the United States and northern Mexico. It lives mainly between rocks and between pieces of wood or firewood. In Oklahoma (USA) there are about 100 annual cases of poisonings by this species.
It is relatively small for the genus, reaching up to 9 mm in length. Its abdomen is covered by short mushrooms that give it a smooth appearance. The female lays an average of 50 eggs per ootheca.
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