LOXOSCELES LAETA: CHARACTERISTICS, HABITAT, NUTRITION, REPRODUCTION - BIOLOGY - 2025

The fiddler spider (Loxosceles laeta) is a species of South American arachnid whose venom has highly lethal compounds. It belongs to the genus Loxosceles, being the largest species in this group. It owes its name to the violin figure that forms in the cephalothorax, as a contrast between the black marks and the brown background of this part of the body.

This species has very particular characteristics. It has six eyes, instead of eight like the rest of its kind. Their movement is very slow, but if they are under threat, they can turn their body, jump and run at great speeds.

Caption: User: Mampato, via Wikimedia Commons

Its natural habitat is distributed mainly towards the southern part of South America, being found in Argentina, Brazil, Peru, Uruguay, Ecuador and Chile. However, cases of Loxosceles laeta have been reported in other countries, such as Canada, the United States, Mexico, Australia, Finland, and Spain.

During their feeding they can store large amounts of nutrients, allowing them to go long without eating or drinking water. This contributes to the spread of fiddler or corner spiders, as they are also known, as they can travel hidden among fruits or crates without requiring food for their survival.

Loxocelism

The poison that Loxosceles laeta produces could be fatal to man, depending on the relationship between the amount inoculated and the mass of the individual. Its action is necrotic and proteolytic, since it dissolves body tissues, causing cell death.

This lethal substance is made up of powerful enzymes that destroy everything that has proteins. Research indicates that it can be up to 15 times more toxic than cobra venom and about 10 times more powerful than a sulfuric acid burn.

In addition to this, it can easily and quickly penetrate the gallbladders and liver, destroying this important organ in a very short time.

The anaphylactic condition suffered by the organism that has received venom from the violin spider is known clinically as loxoscelism.

Symptoms

The venom is hemolytic and dermonecrotic, destroying the red blood cells of the body and the skin of the affected individual.

Symptoms can be cutaneous or visceral. In most cases the bite is painful. The skin lesion may begin with redness, swelling, and around the bite it may turn grayish-blue.

If left unattended, the lesion can develop necrosis, generating an ulcer that will heal very slowly, taking up to four months.

Only a low percentage of patients develop visceral loxoscelism, which begins between 12 and 24 hours after inoculation of the venom. Your symptoms may include palpitations, high temperatures (fever), joint pain, blood in the urine, nausea, and jaundice.

It is extremely important to control any type of loxoscelism during the first 24 to 48 hours. If in doubt, it is advisable to go to the doctor.

Preventive measures

Since the bite of the violin spider is almost fatal, it is important to recognize the signs that warn the presence of this animal in certain areas of the house.

One way to know about the existence of this animal is to observe the environment in detail, in search of exoskeletons, since these are released in the molts of its development.

The other way is detecting in the corners of the walls, the shelves or the drawers, the presence of dense and white cobwebs, similar to a cotton.

General characteristics

Size

In its adult stage, the female fiddler spider measures between 7 and 15 millimeters. The male is approximately 6 to 12 millimeters long.

Body

Its body is robust and morphologically divided into two well differentiated segments; the opistosoma (abdomen) and the cephalothorax.

These animals have sexual dimorphism, the females are usually larger and with a larger opistosome than the males.

Eyes

Unlike the vast majority of arachnids, which have 8 eyes, the Loxosceles laeta species has 6. These are organized in dyads, distributed in the shape of a triangle. On the front are a large pair of eyes and on the sides there are two smaller pairs.

This characteristic of the visual organs provides the animal with a visual field of 300 °, which is highly beneficial for the capture of its prey.

Color

This South American species has a brownish-brown tone, although it could also present gray, yellowish-brown or reddish colors, even black. The big difference between the tones could be due to the hairs and mushrooms that it has on its body.

The cephalothorax is brown in color, with black markings on the dorsal area of ​​the thorax, which give it the image of a violin. The abdominal region is a single color, generally darker than the rest of the body.

Cheliceros

The fiddler spider has inoculating teeth, which are arc-shaped. The chelicerae are located horizontally in the lower part of the prosoma. When they bite, they cross like tweezers.

This structure, in its internal margin, is keratinized, extending forward. The distal ends end in fine black needles, where a kind of articulated nail is located.

Fur

Its body is covered by two kinds of hair, some long and erect, and others branched and lying down. The legs, in the area of ​​their tarsi, have hairs that fulfill tactile functions.

Stridulatory apparatus

This insect has a stridulatory apparatus, which develops in the early stages of maturation. It is of a palpal chelicerae character and its function is related to reproduction.

Extremities

Its legs are made up of the femur, tibia, metatarsal, and tarsus. These have similar characteristics in males and females, except that males have them longer, both in relative and absolute size.

Haplogins

The Loxosceles laeta is characterized by having simple genitalia. The females of this species do not have an epigine and in the males the tarsal socket is not differentiated in the pedipalps.

Poisonous glands

The Loxosceles laeta species has a body system that produces a highly toxic and deadly chemical. This apparatus is made up of a pair of glands, located inside the cephalothorax region.

The venom produced there contains neurotoxins, potent cytotoxins, and hemotoxins. This substance is used by the violinist spider to kill its prey, and then digest it.

Taxonomy

Animal Kingdom.

Subkingdom Bilateria.

Superfilum Ecdysozoa.

Phylum Arthropoda.

Arachnid class.

Order Araneae.

Sicariidae family.

Genus Loxosceles

Species

Habitat and distribution

Fiddler spiders, also known as Chilean recluse spiders, are widely distributed in South America, especially Chile. Within this continent they have also been found in Brazil, Uruguay, Ecuador, Peru and Argentina.

In recent years, they have spread to Colombia and to some Central American countries, such as Honduras and Guatemala.

Isolated populations of Loxosceles laeta have been reported in Mexico, Australia and Spain, in addition to various regions of the United States (Los Angeles, Kansas, Massachusetts and Florida) and Canada (Toronto, Vancouver, Ontario, British Columbia and Cambridge).

In Finland, in the Helsinki Museum of Natural History, there is a colony of fiddler spiders. It is believed that it arrived there around the 60s or 70s. However, it is still inexplicable how this tropical animal traveled more than 13,000 km to inhabit the basement of a museum that is located a very short distance from the Arctic Circle.

There may be several causes that explain this distribution so far from its ecological niche. One of these can be attributed to the fact that some species traveled to distant lands hidden in agricultural products. They were also able to hide in the boxes containing fruits, vegetables or in pieces of wood.

Habitat

The violinist spider is a synanthropic species, since it is adapted to live in ecosystems that are anthropized or urbanized by man. This coexistence with humans is favorable for Loxosceles laeta, since they can meet their basic and developmental needs far from their natural predators.

However, for the human being it is highly harmful because it increases the risk of being bitten by this highly poisonous spider, which can bring fatal consequences if the injury is not treated in time.

They usually hide in corners of rooms, in attics, behind pictures, underneath furniture, among clothes, and on high shelves in closets.

In the area around the house, garden, or patio, fiddler spiders hide in dark, damp places. Thus, they can be found under wooden logs, in rubble and under stones.

Rural and urban area

They usually inhabit the different internal areas of the house, which is known as the domiciliary sector, or in the patios and gardens that surround it (peridomiciliary sector).

In some studies carried out in Mexico and Chile, it is observed that there is a factor that helps them spread more easily in urban homes than in rural ones; the proximity between the houses. If there are fiddler spiders in a home, they can easily invade the next one.

However, if the number of individuals living in an urban and rural infected house is compared, in the latter they could be found in greater numbers. This could be due to the characteristics of the construction of these rural houses, where their walls are usually made of adobe, and the deficiency in ventilation and lighting.

In this way, the violinist spider finds an environment conducive to growth and multiplication, in which it can hardly spread to neighboring houses, because the houses are usually far apart from each other.

Nutrition

Loxosceles laeta is a carnivorous animal, its diet is based mainly on insects. Among their favorite prey are moths, flies, cockroaches, crickets, and some other small arthropods. You can capture them in two ways; hunting them at night or trapping them with their net.

This animal does not have to worry much about its food. The cobweb's strategic location, coupled with its sticky and tough character, frequently causes some of its favorite prey to get trapped in it.

The digestive system is divided into three parts: the stomodeum, the mesodeo, and the proctodeo. Its feeding is carried out mainly through the suction of the liquids that are formed as a product of the disintegration of the dam.

Digestive process

Once it captures its prey, whether it has been hunted or trapped in the web, the fiddler spider pounces on it, injecting it with its powerful venom.

When the prey dies, the spider continues to retain it with chelicerae, through which it pours the digestive juices produced by the midgut (mesodeus). These will fulfill the function of decomposing the food.

These digestive enzymes quickly convert food into a kind of nutrient broth, which is sucked into the pre-oral cavity, located in front of the mouth.

Their oral muscles can be arranged longitudinally and inserted externally, allowing them to modify their volume and diameter. This makes it the main aspiration organ of the fiddler spider.

The suction action is complemented by the esophagus, thus contributing to the fluid reaching the mid-section. In this is the central tube and several auxiliary diverticula, located in the opistosoma and the cephalothorax.

In the walls of the mesodeo there are cells that produce enzymes that complement chemical digestion. A part of the food already digested is stored in the stomach, specifically in its multiple diverticula, while the rest is absorbed by the wall of the mesodeo.

The proctodean of this species is formed by the intestine and the anus, where waste is stored and subsequently expelled from the body.

Research

The insects that fiddler spiders eat are relatively large. Its predatory efficiency and its great ability to prey bulky animals is due to the combination of extracorporeal and intracellular digestion.

In order to expand the knowledge about this stage of digestion, several investigations have been carried out regarding the protein composition of the diverticula and the digestive fluid.

These show that digestive enzymes contain hydrolases and astazines, suggesting that the latter play an important role in extracorporeal digestion. It was shown that the digestive fluid originates in the diverticula, and that these participate in both extracorporeal and internal digestion.

In addition, several proteins that are produced in the digestive organs were identified, an aspect that was previously directly associated with the venom glands of Loxosceles laeta.

Reproduction

Because fiddler spiders are haplogins, females lack external sexual organs to identify when they are sexually mature.

However, the scope of this stage is usually accompanied by a darkening of the cephalothoracic region and a better visualization of the epigastric fold.

In the male, the evidence that indicates its sexual maturity is the transformation of the palp, as part of the copulatory apparatus of the species.

The female is selective about the male with whom she will copulate. During courtship, the male performs a kind of dance around her, jumping up and down with the intention of impressing her. They could also offer him some prey, with the intention that he is the chosen one.

Sexual organs

The male reproductive system is made up of the paired testicles, tubular in shape and the vas deferens, with a fairly small diameter. These merge in the area near the genital opening, forming the ejaculation duct.

This duct opens into the gonopore, in the epigastric sulcus. The ejaculatory duct is discreet, being able to enlarge or widen towards the vas deferens.

Sperm and the various secretions that make up the seminal fluid flow from the gonopore. Because males lack accessory glands, this secretion is produced by the somatic tissue that make up the testes and vas deferens.

Females have a pair of ovaries and an abdominal passage that allows the eggs to emerge. The fiddler spider has a small opening near the epigastric groove, which runs through the abdomen in its ventral part.

Within these openings are the entrances of the spermathecae, blind sacs where the male deposits the sperm during copulation.

Reproductive process

The reproduction of Loxosceles laeta has several special characteristics. First of all, it usually occurs in the warmest months of the year: May, June and July. Another outstanding aspect is that males transfer sperm through their pedipalps, which are modified into a secondary copulatory organ.

The organs involved in copulation are not associated with the primary genital system, located in the opisthosoma.

In copulation, after the male and female have been in contact for a while, the female raises the cephalothorax and the first pairs of legs. The male extends the palps, which are part of the stridulatory system, forward, introducing them into the female reproductive system.

The copulatory stage can last a very short time, although it can be repeated three or four times. Sperm from the male is always transferred in an encapsulated and inactive manner to the female.

The spermatophore is covered by a kind of "cloth", which is formed when the sperm has been exposed to the environment. After this, the female expels the eggs into the abdominal passage, where they are fertilized by the sperm that travel from the spermathecae.

Female fiddler spiders lay their eggs in ootheques, which could contain an average of 89 eggs. About two months after mating, the eggs will hatch, hatching the young.

These small nymphs, if survival conditions are extreme, could reach cannibalism. Those that manage to survive will become adults when they reach around one year of age.

Mating may occur up to twice over a 3-month period, leading to a double batch of egg laying per year.

Behavior

The violinist spider is a shy, territorial, hunter and nocturnal insect, being even more active during summer nights. In cold seasons, its vitality decreases noticeably. This species likes hidden and dark places, from which it only comes out to hunt.

If he sensed any threat, he would be able to react very quickly, running full speed in search of shelter. It could also jump up to 10 centimeters high, to sneak out of danger.

They are generally not aggressive, preferring to flee than attack. However, when they do, they first raise their front legs as a warning signal, signaling to the opponent that they will not back down.

If they decided to attack, they would use their best weapon: powerful poison. This substance could kill a human in a relatively short time.

The weaver spider

Loxosceles laeta weaves an irregular cobweb with a messy pattern. In the horizontal direction it has another net, forming a kind of short hammock. These could be located anywhere these insects live: the shadowy corners of the walls, drawers or shelves.

It has a thick, cottony, sticky texture and the color is white. Its length could measure between 4 and 8 centimeters, with a thickness of 1 centimeter. The fiddler spider spends a long time in the web, which serves both to rest and to capture its prey.

Although the fiddler spider is sedentary, if it needed to get away from the web, it wouldn't do it too far, although occasionally males might.

Sexual behavior

The fiddler spider has sexual behaviors that can be categorized into five stages:

Pre-courtship

This stage corresponds to the moment of recognition of the couple. Eleven different movement patterns occur in it, culminating in tactile contact between male and female.

Courtship

After touching each other, the male may hit the female's legs. Then the couple positions themselves face to face. The male stretches his front legs, gently touching the female's cephalothorax. Later, it returns to its original position, hitting the female again on his leg.

In this phase, the female may be receptive to the courtship of the male. In this case, her forelimbs would show a slight tremor. If the female was not receptive, it would raise the cephalothorax when touched by the male, and could even attack it.

Pre-copulation

Since the male has his front legs on top of the female, he will now try to touch her in the lateral region of the opisthosoma.

Copulation

At this stage, the male is already positioned before the female. To start copulation, it bends its legs, getting much closer to the female's body. After this, the male moves his pedipalps, touching the mouthparts of his partner.

Next, the male proceeds to lower the cephalothorax, moving under the female. In this way, it stretches the pedipals to insert them into the female's genital grooves.

The pedipal emboli remain inserted for a few seconds, however, this action could be repeated several times. At the last insertion of the plunger, before the male withdraws, a very aggressive attack by the female could occur.

Post-copulation

After copulation is complete, the male may remove the legs from the female's cephalothorax or stretch them out. It could also show the pre-copulatory patterns again. Some specimens usually take advantage to clean the pedipalps, passing them through the chelicerae.

References

1. Willis J. Gertsch (1967). The spider genus loxosceles in South America (Araneae, Scytodidae). Bulletin of the American Museum of Natural History, New York. Recovered from digitallibrary.amnh.org.
2. Andrés Taucare-Río (2012). Synantropic dangerous spiders from Chile. Scielo. Recovered from scielo.conicyt.cl.
3. Wikipedia (2018). Loxosceles laeta. Recovered from en.wikipedia.org.
4. Fuzita FJ, Pinkse MW, Patane JS, Verhaert PD, Lopes AR. (2016). High throughput techniques to reveal the molecular physiology and evolution of digestion in spiders. NCBI. Recovered from ncbi.nlm.nih.gov.
5. Peter Michalik, Elisabeth Lipke (2013). Male Reproductive System of Spiders. Research gate. Recovered from researchgate.net.
6. Hugo Schenone, Antonio Rojas, Hernã • n Reyes, Fernando Villarroel, Andgerardo Suarez (1970). Prevalence of Loxosceles laeta in houses in central Chile. The American Society of Tropical Medicine and Hygiene. Recovered from koivu.luomus.fi.
7. Ministry of Health, Government of Chile (2016). Guide for the Management of Corner Spider Bite - Loxosceles laeta. Recovered from cituc.uc.cl
8. Demitri Parra, Marisa Torres, José Morillas, Pablo Espinoza (2002). Loxosceles laeta, identification and a look under scanning microscopy. Recovered from scielo.conicyt.cl.
9. ITIS (2018). Loxosceles laeta. Recovered from itis.gov.
10. Marta L. Fischer (2007). Sexual behavior of Loxosceles laeta (Nicolet) (Araneae, Sicariidae): influence of the female dog. Recovered from scielo.br.