Introduction

Arachnids are a large group of invertebrates and represent a megadiverse lineage of arthropods with more than 955000 described species, but an estimated 1 to 1.5 million species await naming^1-3, with a cosmopolitan distribution⁴. In the Americas, there are genera of arachnids that stand out for their medical importance, Loxosceles, Phoneutria and Latrodectus⁵. In Bolivia, the genus Latrodectus, commonly known as "black widow". In some regions of the valleys known as "mico mico", while in the western part "huairuro”⁶.

The genus Latrodectus is considered a public health problem due to its chelicerae bite⁷. This structure stores and releases a poison, highly harmful to human health, a toxin (α-latrotoxin) that causes the massive release of neurotransmitters^7,8, producing severe intoxication, generating different symptoms such as: severe inflammation, fever, intense pain, hallucinations, muscle stiffness, heart rhythm disorders, mainly paralysis of the nervous system^9,10.

Typical habitats for this type of arachnid vary from dark, damp, damp places to those with lots of vegetation⁷. However, as cities have grown in recent decades, ecosystems have changed, causing local species to adapt and broaden their preferences to use habitats near dwellings or other structures. Consequently, they could be considered as synanthropic arachnids, i.e. they tend to settle in urbanised areas¹¹, whose climatic conditions, food and environment play an important role for their stabilisation¹².

The presence of individuals of the genus Latrodectus from the year 2021 to date has been confirmed in different sectors of the department of Oruro. For this reason, the aim of the present study was to determine the presence of the genus Latrodectus in the Department of Oruro.

Materials and methods

Study area. The arachnids came from urban and rural areas of the department of Oruro, located in western Bolivia, at an altitude of 3800 m.a.s.l. between 17°18' 37'' and 19°55' 46'' South Latitude and 66°12' 12' 12'' and 69°05' 05' 05'' West Longitude (central altiplano). Bordering the departments of La Paz, Potosí, Cochabamba, and the Republic of Chile¹³.

Semi-cold, semi-arid climate with dry winter, average temperature ranges from 8 to 18° C, precipitation varies between 190 to 570 mm per year, precipitation depends on the area of the department¹³.

Specimen collection. Specimens of arachnids dating from the years 2021-2022 from different areas, which were sent by the Departmental Health Service (SEDES Oruro), were evaluated. The specimens were carefully captured by SEDES Oruro staff, using perforated plastic jars to avoid leakage. The samples were then sent to the National Institute of Health Laboratories (INLASA) for identification and recognition. In the case of dead specimens, they were preserved in 70% alcohol and sorted in the wet collection with their respective coding⁶.

Dead specimens were analysed, a branded stereo microscope (Ken-α-Vision, 20X magnification) was used and dichotomous keys were consulted^6,10.

Databases. Using Microsoft Excel software, a data record was made for each of the samples used from the INLASA collection. The following information was obtained: a) code, b) sample c) department d) municipality e) place of capture and f) sample status.

Georeferencing. The samples from INLASA's wet collection did not have precise coordinates. Therefore, an approximate georeferencing was assigned to each of the collection points according to reference locations. Using the Google Earth Pro v. 7.1.8.3036 programme, obtaining latitude and longitude data⁶.

With the coordinates obtained, the locations of the specimens were georeferenced and a map of the presence of the genus Latrodectus in the department of Oruro was drawn up with the Arc Gis v.10.3 computer program, using the WGS 1984 UTM Zone 19 S geographic coordinate system. In addition, the vegetation layer was used to obtain more references for each place, and the main square of 10 de Febrero was considered as the main point in the city of Oruro¹³.

Results

Genus recognition. Forty-one specimens of the genus Latrodectus (Figure 1) were assessed for their morphological characteristics. Most were females (40 individuals) and 1 male.

Figure 1 Female specimen of genus Latrodectus  

According to the dichotomous keys¹⁰, the taxonomic evaluation criteria for specimens of the genus Latrodectus belong to the family Theridiidae. In their morphological characteristics it was recognised that they have black cephalothorax, abdomen and legs. Females had a larger body size than males, showing sexual dimorphism. They also have a prominent, globular abdomen, with a noticeable or reduced presence of the red hourglass pattern on the opisthosoma, which varies between individuals. The lateral eyes are separated. The chelicerae have no teeth. The fourth pair of legs has hairs arranged in a comb-like pattern^6,10. The legs are medium-sized, with formula 1423¹⁴.

Figure 2 Presence of the genus Latrodectus in the department of Oruro 

Georeferencing. The 41 specimens were captured in 3 municipalities in the department of Oruro. In the capital city, the largest number of records was captured, with the genus being found in 15 different locations. The remaining specimens were found in the municipality of Machacamarca and between the municipalities of Challacollo and Toledo (Figure 2). The greatest number of specimens of the genus were captured in the months of March, July and November.

The arachnids were found in different locations both outside and inside buildings in rural, peri-urban and urban areas, with a predominance of houses under construction, mainly open places, close to the pavement, with surrounding vegetation, with greater exposure to the environment. While the specimens from urban areas were mainly located in buildings with a higher number of people, schools, public universities, health centres and housing estates (Figure 2).

In addition, this genus was mostly located in predominantly dwarf evergreen scrub areas. With the exception of the Machacamarca Health Centre, which is close to seasonal low graminoid herbaceous vegetation (Figure 3).

Figure 3 Map of vegetation types in the department of Oruro 

Discussion

In Bolivia, no dangerous arachnids have been recorded at higher altitudes (3000 m)^15,16. However, through this study their presence and distribution at higher altitudes of the range (3735 m). Thus its presence in localities in 6 departments (La Paz, Cochabamba, Santa Cruz, Tarija, Potosí and Chuquisaca), but not in Oruro, which even extends its distribution to urban areas⁶.

The specimens of the genus Latrodectus captured in the city of Oruro are classified as synanthropic arachnids, due to their ability to adapt to a variety of physical and biological conditions in urban ecosystems^17-19. They take refuge in different types of cover and/or surfaces including: under stones, among debris, logs or holes, or close to vegetation^18,20.

Vegetation is an important factor for their presence^18,21, they manage to establish themselves and have food available^12,22,23. Oruro has a predominant type of vegetation such as scrubland, which is an ideal habitat for these arachnids^23,24. These environments are mostly found outside homes or buildings²⁴.

They can be categorised as seasonal synanthropic individuals, they can be in natural areas as well as in dwellings, but they do not plague spaces because they are not always found in the same place^11,23. Therefore, it can be inferred that spiders choose a space that is not frequently disturbed to establish themselves²⁰.

Arachnids could enter and settle inside buildings using their dispersal modes known as "ballooning" or "rappelling", which allow them to move long distances from one place to another through their webs despite air currents²¹. Another way of entry would be by walking on surfaces such as the ground or walls to closer locations²⁵, or through anthropogenic activity such as the use of transport, transfer of materials and trade would help their dispersal to more disturbed and/or urbanised areas, increasing their distribution to new sites^8,12,17. This would explain the increase and expansion of the genus Latrodectus in urbanised areas.

Generally, inside buildings there are differences between the characteristics of each environment^26-28, in which temperature and humidity, food, the structure of the place, the concentration of people in the spaces, or the combination of these factors, make each site unique in its environment for arachnids^12,19,23,27.

In such spaces, they mainly settle down to shelter from low temperatures, which is why they would be qualified as strategic sites. In this way, each environment would generate a microhabitat suitable for their settlement and therefore these sites would be more favourable for their survival and colonization^19,27,28.

Therefore, these arachnids are considered to be of great importance in the ecosystem, as they are predators, inhabiting places among leaf litter and low vegetation²⁹ to obtain food, benefiting humans as natural pest controllers^22,23,30. However, it would be necessary and relevant to know the places where arachnid populations concentrate and reproduce. Mainly those places and/or establishments where a greater number of people congregate in a given place, as this would increase the risk of being bitten by the arachnid, which would represent a major medical problem¹².

Although these arachnids are not aggressive, it is important to educate the population about their morphological characteristics and their medical importance. They react when they feel attacked as a self-defence mechanism or if their nest is being disturbed³¹. Or if a person sits on or has close contact with the arachnid, they are more likely to receive a lethal bite, which can cause latrodectism^32,33.

The substance released by its chelicerae is more potent than the venom of the rattlesnake (Crotalus durissus) because it has more toxins present in the venom which is highly damaging to the nervous system, with symptoms such as irritability, hyperactivity, agitation, vomiting and muscle spasms beginning to appear within minutes³⁴.

So far, seven cases of black widow bites have been reported in the department of Oruro³⁵. However, INLASA has the antivenom antilatrodectus (which efficiently neutralises the toxic effect caused by the venom) to deal with the emergency.

Urban areas have expanded massively, causing a noticeable change in the environment and fragmentation of natural sites. Hence, more studies on synanthropism in arachnids in Bolivia are needed. In terms of the diversity of urban spiders, the differences between spider communities, the effects of environmental conditions, among others. To understand the effect of urbanisation on spider populations with anthropogenic activity^18,36.

Therefore, in accordance with the above, it has been noted that specimens of the genus Latrodectus are highly adaptable to the environmental conditions of the city of Oruro. Due to the number of individuals evaluated and collected in a single department, in relation to Fernández & Castro⁶, although they had a greater number of specimens examined, these were in different localities in 6 departments. In this study, 41 specimens were found close to each other in only one department.

The genus Latrodectus can establish itself in urban environments both outdoors and indoors, withstanding environmental changes, adapting to new microhabitats and possibly also being influenced by anthropogenic activities. It is therefore recommended to clean with extreme care, especially those places where there is worn material such as wood or leaf litter, to prevent spiders from establishing themselves in these areas. Maintenance should also be carried out between walls or corners in homes to avoid their establishment due to the danger they represent.