Boletín de la Sociedad Zoológica del Uruguay, 2024

Vol. 33 (1): e33.1.4

ISSN 2393-6940

https://journal.szu.org.uy

DOI: https://doi.org/10.26462/33.1.4

ABSTRACT

The aim of this work was to provide information on

arachnidism in northern Misiones province. We used the

database (2017-2023) of the National Institute of Tropical

Medicine. We recorded 62 incidents, classified as mild,

only one moderate. Phoneutrism was the most frequent

intoxication (66%). We present the first case of

Loxosceles hirsuta Melo-Leitão, 1931 bite. Cases

occurred throughout the year, with peaks in November

and May, and occurred mainly on the hands or feet. The

main affected groups were residents aged 0 to 10 and

22-32 years. Female/male ratio = 0.51. Fifty-four percent

of cases occurred at home and 29% in rural areas.

Stinging pain and erythema were the most frequent local

symptoms. Spider bites were not correlated with climatic

variables and no seasonality was evident. Arachnidism in

northern Misiones involves native and frequent spiders,

and is possibly facilitated by local human habits and

lifestyles. Taxonomic diagnosis was beneficial in

determining and monitoring the assemblage of spiders of

medical interest in the region.

Key words: Epidemiology; Loxosceles; Phoneutria;

Toxicology; Public health surveillance

RESUMEN

Picaduras de araña en el bosque atlántico argentino

(2017-2023). El objetivo de este trabajo fue proporcionar

información sobre el araneísmo del norte de la provincia

de Misiones. Utilizamos la base de datos (2017-2023) del

Instituto Nacional de Medicina Tropical. Registramos 62

incidentes, clasificados como leves, sólo uno moderado.

El foneutrismo fue la intoxicación más frecuente (66%).

Presentamos el primer caso de mordedura de

Loxosceles hirsuta Melo-Leitão, 1931. Los casos se

produjeron a lo largo de todo el año, con picos en

noviembre y mayo, y se produjeron principalmente en las

manos o los pies. Los principales grupos afectados

fueron los residentes de 0 a 10 y 22 a 32 años. Relación

mujer/hombre = 0,51. El 54% de los casos se produjeron

en el hogar y el 29% en zonas rurales. El dolor punzante

y eritema fueron los síntomas locales más frecuentes.

Las mordeduras no se correlacionaron con las variables

climáticas y no se evidenció estacionalidad. El

araneísmo en el norte misionero involucra arañas nativas

y frecuentes, posiblemente facilitado por los hábitos y

estilos de vida humanos locales. La identificación

taxonómica resultó beneficiosa en la determinación y

monitoreo del ensamble de arañas de interés médico en

la región.

Palabras clave: Epidemiología; Loxosceles;

Phoneutria; Toxicología; Vigilancia de la salud pública.

INTRODUCTION

Aranchnidism is defined as the syndrome of

poisoning caused by the inoculation of toxins by the

bite of a spider (Moyano, 2008). Worldwide, 51.908

spider species distributed in 138 families and 4.375

genera have been described (World Spider Catalog,

2024), but only some species of the cosmopolitan

genera Latrodectus Walckenaer, 1805 (Theridiidae),

Loxosceles Heineken & Lowe, 1832 (Sicariidae) and,

less frequently, Phoneutria Perty, 1833 (Ctenidae) in

South America and Atrax O. Pickar-Cambridge, 1877

(Atracidae), endemic to Australia, are considered of

medical importance (Porras-Villamil and Olivera,

2020).

In the Americas, Latrodectus spp. are widely

distributed, but some species of Loxosceles are of

major medical interest, especially in Chile, Colombia

and the United States; in Brazil and Colombia,

Bol. Soc. Zool. Uruguay (2ª época). 2024. ISSN 2393-6940Vol. 33 (1): e33.1.4

SPIDER BITES IN THE ARGENTINIAN ATLANTIC FOREST (2017-2023)

1* 1,2

Carlos Ariel López and Esteban Manuel Couto

1Instituto Nacional de Medicina Tropical, Ámbar y Almafuerte s/n, Puerto Iguazú, Argentina.

Teléfono: +54 11 3757 625002 interno:1157. CP: 3370.

2Hospital-SAMIC Iguazú “Dra. Marta T. Schwarz”, Av. Victoria Aguirre 142, Puerto Iguazú, Argentina. CP: 3370.

*Autor para correspondencia: lopez_arielc@yahoo.com.ar

Fecha de recepción: 28 de diciembre de 2023

Fecha de aceptación: 01 de junio de 2024

LÓPEZ Y COUTO

Phoneutria spp. should also be considered (

Gómez and Gómez, 2019).

According to data from the National Health

Surveillance System, in Argentina there are 1200 to

2000 spider bites/year (Orduna, Lloveras, de Roodt,

Costa de Oliveira and García, 2012), and occasionally

serious acute intoxications occur, reporting 1-2

deaths/year (Casas, de Roodt, García and Fandiño,

2013). The species of medical importance in Argentina

belong to the three genera, the most important being

Latrodectus (the black widows), followed by

Loxosceles (violin spider, -with Lo. laeta (Nicolet,

1849) causing most of the accidents-), and Phoneutria

nigriventer (Keyserling, 1891) (banano spider) with

fewer cases in northern Argentina (Cabrerizo et al.,

2009; Casas, de Roodt, García and Fandiño, 2013).

About 90% of the accidents with Lo. laeta in the

country develop the mild form of cutaneous

loxoscelism, although it can evolve into lesions in the

form of ulcers that do not heal and require reparative

surgery, leaving some esthetic sequelae (Cabrerizo et

al., 2009). There are few known fatal cases of

phoneutrism, the highest susceptibility is observed in

children and there are few reports of sequelae of

poisonings (Salvatierra and Ramos, 2018).

The province of Misiones (located in the extreme

northeast of the country) ranks third in the number of

spider bites, with approximately 200 cases/year,

surpassed only by Santiago del Estero and Córdoba

(Orduna, Lloveras, de Roodt, Costa de Oliveira and

García, 2012). The city of Puerto Iguazú is located in

the extreme northwest of the province of Misiones,

being part of the triple border with Brazil and

Paraguay, and forms the buffer area of the Iguazú

National Park and its falls, one of the largest and best-

preserved patches of Atlantic Forest in the world

(Ribeiro, Metzger, Martensen, Ponzoni and Hirota.

2009). Recent studies show that the largest number of

scorpion species of sanitary interest in the country are

found in this locality (López, 2021), and Iguazú

National Park has the largest number of species of

venomous snakes (Giraudo, Arzamendia, Méndez

and Acosta, 2009). However, the characteristics of

spider bites in the city and its area of influence have

not yet been described.

The present work aims to characterize the eco-

epidemiology of spider envenomation, provide a brief

description of the species of medical interest and

propose accident prevention measures in the

Argentinian extension of the Atlantic Forest.

MATERIALS AND METHODS

We conducted a descriptive observational study

based on the records between 2017 to 2023 of the

Taxonomy Service (TS) of the National Institute of

Brazil,

Pinto-Leite, Almeida-Silva, Lira da Silva and

Brescovit, 2009;

Tropical Medicine (INMeT) based in Puerto Iguazú.

The TS has been operating since 2013, with the

primary objective of offering assistance in the

identification of poisonous species of health interest to

the provincial and national health system. At the local

level it is linked to the Infectious Diseases Service of

the "Dr. Marta T. Schwarz" Hospital. It also receives

consultations and provides advice to the local

population on these animals. The specimens were

received at INMeT, where the data of the person who

delivers them (name of the collector, date, address,

telephone number, etc.) and the details of the discovery

of the animal (date, place, circumstances of the finding

and comments) were recorded. After identification, a

written report was prepared with the determination and

the degree of sanitary importance of the species.

Starting in 2017, the TS began using the virtual

messaging service for the uninterrupted service of

species determination by images, expanding the scope

to other localities and provinces. For the present

communication the data used were mainly from Puerto

Iguazú, and also Puerto Libertad, San Antonio,

Comandante Andresito, Bernardo de Irigoyen and

Eldorado, all urban centers in the extreme north of the

province of Misiones, within the Interior Atlantic

Rainforest. Notifications of accidents are also received

from medical personnel, with the species involved

already identified by the attending physician

(secondary data). All information, without individual's

personal data, was stored and safeguarded in digital

files, while biological specimens in good condition were

deposited in the collection of arachnids of the TS, for

didactic and research purposes (acronym: INMET#,

curator: CA López). Individuals of Loxosceles hirsuta

Mello-Leitão, 1931, 25 to 30 females and one to five

males, were kept in plastic Petri dishes in laboratory

conditions, to improve reproduction techniques. These

individuals were fed three to four times per month

mainly with ants and small grasshoppers. Males or

females were entered into the female enclosures to

evaluate their behaviors such as predation, courtship,

copulation, egg laying, incubation and hatching.

Data analysis

For primary and secondary data, TS records were

available for spider bites recorded in 2017-2023. The

information was consolidated in a matrix where the

selected variables were: spider species, date of the

accident, geographical location of the accident,

environment of the accident (categories: domicile,

backyards, rural and urban), anatomical location of the

bite, age, gender, activity performed by the person at

the time of the accident, the symptomatology and the

standardized classification of the accident determined

by the physician (mild, moderate, severe). This

information is available upon request via e-mail:

odanielsalomon@gmail.com. The occurrence of the

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3Spider bites in the Argentinian Atlantic Forest (2017-2023)

Bol. Soc. Zool. Uruguay (2ª época). 2024. ISSN 2393-6940Vol. 33 (1): e33.1.4

Fig. 1: Frequency of spider bites accumulated per month (multiplied x 50) between 2017-2023 in the Argentinian Atlantic

Forest. Orange line: Mean monthly maximum temperatures (Celsius degrees) during the period. Gray line: Mean

accumulated rainfall (in mm) per month during the study period.

Fig. 2: Frequencies of spider bites by age category in the study period (2017-2023) in the Argentinian Atlantic Forest.

LÓPEZ Y COUTO 4

Bol. Soc. Zool. Uruguay (2ª época). 2024. ISSN 2393-6940Vol. 33 (1): e33.1.4

Fig. 3: Frequency of spider bites on body topography in the study period (2017-2023) in the Argentinian Atlantic Forest.

Fig. 4: Frequency of environments where spider bites occurred in the study period (2017-2023) in the Argentinian

Atlantic Forest.

5Spider bites in the Argentinian Atlantic Forest (2017-2023)

accidents was analyzed with respect to average

monthly maximum and minimum temperatures and

monthly accumulated rainfall using a multiple linear

regression model. As a proxy of seasonality,

differences between observed frequencies and

homogeneous distribution of accidents were tested

with G- test of goodness of fit. The "stats" package was

used for the linear fit and "DescTools" for G- test, both

included in the R software (R Development Core Team,

2022). The meteorological data during the study period

was recorded by Puerto Iguazú airport (Office of

Natural Disaster Prevention - OPAD Alerta Temprana

(misiones.gob.ar)

For the spider's identification, specialized literature

was consulted (Gertsch, 1967; Simó and Brescovit,

2001; Martins and Bertani, 2007; Grismado, Ramírez

and Izquierdo, 2014; Magalhaes, Brecovit and Santos,

2017; Caruso, Lauria, de Souza, Casais-e-Silva and

Zingali, 2021; Hazzi and Hormiga, 2021) and

contrasted with the geographical distribution of the

species reported (WSC, 2024). A Carl Zeiss Primo Star

binocular microscope was used to observe the external

morphology, and a Canon SX30 digital camera was

used to take photographs.

RESULTS

In the period 2017-2023, 62 spider bites were

recorded, between one and ten cumulative

cases/month, with an average of 8,9 cases/year. The

accidents were distributed throughout the year, with

peaks in May (autumn) and the highest in November

(spring). Most of the bites occurred between October

and December (40.3 %) (Fig. 1). Phoneutria nigriventer

was the species involved in 66 % of the accidents,

followed by species of the family Lycosidae (8 %), Lo.

hirsuta (5 %) and others species (21 %). In 16% of the

cases, the spider species was not identified. The cases

with P. nigriventer occurred throughout the whole year,

while cases with Lo. hirsuta occurred only during

spring. Only one accident was assigned to Lo. hirsuta

by the TS, the other case was reported by the

physician, with no evidence for identification provided.

The incidence was most significant among locals,

being only two tourists affected. The age group 0-10

years (25 %) and 22-32 years (25 %) had the highest

frequency of accidents (Fig. 2). Accidents were more

frequent in men (66 %), with a female/male ratio = 0,51.

Bites were more frequent on hands (65 %) and on feet

Bol. Soc. Zool. Uruguay (2ª época). 2024. ISSN 2393-6940Vol. 33 (1): e33.1.4

Fig. 5: Main symptoms and signs produced by spider bites in the study period (2017-2023) in the Argentinian

Atlantic Forest.

LÓPEZ Y COUTO

(21 %) (Fig. 3). Fifty-four percent of the accidents

occurred at home when performing domestic duties,

such as cleaning and handling clothing, while 29%

occurred in rural areas (Fig. 4). Pain and erythema

were the most frequently reported local symptom,

followed by, to a lesser extent, edema, pruritus,

paresthesia, paresis, nausea, hypothermia,

hyperthermia, headache, myalgia, bradycardia,

macula, blisters, blurred vision and dizziness (Fig. 5).

The main symptoms were treated mainly with

analgesics and parenteral hydration, and sometimes

also with antihistamines and corticosteroids, without

the need to use antivenom.

All but one bite was classified as mild; one record of

Lo. hirsuta poisoning was classified as moderate.

The females kept individually in Petri dishes

endured more than a year and a half in captivity. The

females covered the bottom of the capsule with cloth

that they enriched until they formed a mattress. In

observations inside the houses, it is the females that

choose a shelter at the entrance of which they weave a

cloth that extends not far from the shelter. Males did not

weave cloth either in the capsules or in the shelters

where they were located inside the houses, their

survival in captivity was much lower than that of

females. Intraspecific predation is common in adults

and juveniles. Ten males were introduced into female's

capsules. One male did not interact with the female,

while the rest quickly began courtship. The courtship

began with the touching of the female's body with leg II

of the male, then the female was placed face to face

with the male, when the male began an alternating

beating of the substrate with the pedipalps, so he lifted

the female with legs I and II exposing the reproductive

apparatus to finally introduce the sperm (Fig. 3 D). The

female remains immobile during the whole process. Of

the ten male exposures only four clutches hatched, the

rest were mostly predated by females (mean number of

eggs: 25.4, max: 33, min: 12; mean number of

incubation days: 59, max: 63, min: 54) (Fig. E and F).

By using the linear multiple regression model we

assessed that there was no correlation between

accidents and temperature or precipitation (R = 0,28,

p-value= 0,78). We determined using the G-test, as a

proxy of seasonality, that the error between the

observed frequencies and null model of accidents

where not statistically significant (G-statistic= 0,075,

df= 3, p-value (X ) = 0,99).

Morpho-ethological characterization of the

species recorded:

Phoneutria nigriventer (Keyserling, 1891)

The genus Phoneutria includes nine species of

Neotropical distribution (World Spider Catalog, 2024),

mainly in Brazil; the species with the most active venom

are P. keyserlingi (F. O. Pickard-Cambridge, 1897) and

P. nigriventer (Vetter and Hillebrecht, 2008). The only

species naturally distributed in Argentina is P.

nigriventer, in the provinces of Misiones, Jujuy, Salta,

Chaco, Corrientes, and Formosa (Grismado, Ramírez

and Izquierdo, 2014). Misiones is where the largest

number of cases and deaths caused by this species

have been recorded (de Roodt et al., 2016). Phoneutria

nigriventer individuals exceed 18 cm in total length

(from the tips of the legs 1-5, extended). Females are

more robust than males, but males have longer legs

(Fig. 1 A and B). Their dorsal coloration varies in shades

of brown, grayish or greenish, which makes it difficult to

detect them for both prey and predators in the jungle

environment. The cephalothorax is high, with a

noticeable longitudinal black dorsal line, in older

specimens it becomes a stain that can cover almost the

entire carapace. A dark line contacts the base of each

chelicera with the anterior and posterior lateral eyes,

also known as "divergent marks" (Fig. 1 C). Black

spines with a conspicuous light spot at their base are

observed on the leg segments closest to the body,

more abundant and visible on the dorsum of the femur

and tibia (Fig. 1 C). The basal part of the chelicerae is

covered by pinkish-orange hairs (Fig. 1 C) from which

the black fangs protrude. With scopulae on the

underside of the first segments of the pedipalps, tibiae

and tarsi (Fig. 1 C, E and F). The abdomen has dorsally

two longitudinal and parallel series of four dark spots

connected by light leaf-shaped oblique spots. Ventrally

the legs are black with a pair of contrasting white spots

on the distal end of femur and tibia, the first two tibiae

have two paired rows of five erectile spines (Fig. 1 D

and E). The sternal region is reddish or black. The

abdomen has a reddish-orange background with a

black spot arising from the pedicel, which may be very

small or absent in males or cover the entire abdomen in

females (Fig. 1 D). The eight eyes are grouped in three

rows -2, 4, 2-. It does not build webs, preys are

captured by stalking on logs, leaves or on the ground,

including insects, arachnids and also small vertebrates

such as amphibians. The silk is used to build the

discoidal egg sac, which can exceed 4 cm in length and

contain more than 1 000 eggs, are fixed under logs or

rocks by a "nursery web" with a disorganized

appearance. The female remains in the care of the egg

sac by positioning herself near or on the structure,

aggressively defending the clutch against any threat.

Its activity is nocturnal. During the day they are found in

shelters, both natural (under logs, stones, in leaf axils

of vegetation), as well as in human waste (debris,

firewood, junk) and in dark corners of buildings. In the

study area they are found in natural environments, but

are also frequent in the backyards and can enter into

the houses when active (Bucherl, 1968). Noteworthy, it

can also display a defense behavior (shared with other

species, but not with species of its own genus)

consisting in the raise of its four front legs, showing the

lower face and the ventral part of the abdomen (Fig. 1

D), which can be accompanied by a lateral swing,

exhibiting the striking aposematic coloration and

Bol. Soc. Zool. Uruguay (2ª época). 2024. ISSN 2393-6940Vol. 33 (1): e33.1.4

appearing larger in size. If the threat persists, or if

inadvertent contact is made, a rapid defensive bite may

be applied. Because of these characteristics, the

species is described as aggressive. Its venom is

neurotoxic, consisting of more than 150 components,

with active peptides and non-peptide compounds, but

there are four neurotoxic complex fractions (PhTx 1-4)

+ + +2

that act on the ion channels of Na , K and Ca in

mammals (PhTx 1-3), while PhTx 4 is toxic to insects

(de Roodt et al., 2016). The poisoning syndrome is

called phoneutrism (de Roodt et al., 2016; de Lima et

al., 2016).

Loxosceles hirsuta Mello-Leitão, 1931

The genus Loxosceles comprises 148 species of

cosmopolitan distribution (World Spider Catalog,

2024), four species are found in Argentina: L. laeta

(Nicolet, 1849), L. spadicea Simon, 1907, L. intermedia

Mello-Leitão, 1934 and L. hirsuta Mello-Leitão, 1931

Bol. Soc. Zool. Uruguay (2ª época). 2024. ISSN 2393-6940Vol. 33 (1): e33.1.4

Spider bites in the Argentinian Atlantic Forest (2017-2023)

Fig. 6: A: Phoneutria nigriventer (♀). B: P. nigriventer, (♂). C: chelicerae with pinkish-orange hairs (red arrow), black line on

domed cephalothorax (light blue arrow), light spots on legs with emerging spine (yellow arrow), divergent markings (green

arrow), and scopulae on underside of first pedipalp segments (white arrow). D: Defensive display characteristic of the species. E:

Tibia I and II with two paired rows of 5 spines (black arrow), first half with scopulae (green arrow). F: Scopulae on palps. Scale

bars: 5 cm. Photographs: CAL.

(Grismado, Ramírez and Izquierdo, 2014). Loxosceles

laeta, widely distributed in the country, is the main

species of medical interest. Loxosceles hirsuta is

distributed mainly in the province of Misiones, with

some historical records in Córdoba, Salta, Tucumán

and recently in Buenos Aires and La Pampa (Peralta-

Seen and Diez, 2023), and is not considered of medical

interest, until the present report. Loxosceles hirsuta

females barely exceed 3 cm in total length, they are

more robust than males, but these have longer limbs,

mainly legs II, being able to double the total length of

females (Fig. 2 A and B). The dorsal and ventral

coloration is brown on the carapace and legs, while the

abdomen is gray with short hairs. On the flattened

cephalothorax, the cephalic region is covered with

hairs, followed by the fovea, with a series of hairs

arranged radially, reinforcing a darker, violin-shaped

coloration ("violin spider"). The chelicerae are fused at

the base. The six characteristic eyes of the family are

grouped in pairs forming a "V" -2, 2, 2- (Fig. 2 C).

Females construct a seemingly disorganized web of

white cottony silk to capture the insects that constitute

their prey, although most of the males' hunting would

take place by active foraging (Cramer, 2015; Canals,

Taucare-Rios, Solis and Moreno, 2016). Our

preliminary observations on courtship and egg laying

were similar for those of Fisher and da Silva (2001) for

Brazilian populations (Fig. 2 D, E and F). Loxosceles

hirsuta is a synanthropic species (cohabits with

humans), preferring dry, undisturbed rooms or

furniture, where several individuals can be found

(Orduna, Lloveras, de Roodt, Costa de Oliveira and

García, 2012, Cramer, 2015). It is a docile species,

biting only when squeezed and, perhaps, if the egg sac

is disturbed. Its venom is necrotizing and hemolytic,

including more than 54 toxic protein compounds (with

i s o f o r m s ) s u c h a s p h o s p h o l i p a s e s D ,

metalloproteases, hyaluronidases, serine proteases,

insecticidal peptides, and non-protein compounds

(Chaim et al., 2011). The poisoning syndrome is called

loxoscelism (Chaves-Moreira et al., 2017).

DISCUSSION

Our results show the importance of taxonomic

diagnosis in the etiological analysis for spider

accidents in one of the areas of Argentina with highest

diversity (Schenone, 2012; Grismado, Ramírez and

Izquierdo, 2014). The methodology implemented

allowed the detection of a high number of accidents

involving P. nigriventer, being the first report of data on

its relevance as species in the country and a useful tool

supporting the practice of emergentology. To the best of

our knowledge, we reported here the first worldwide

accident caused by Lo. hirsuta, requiring medical

attention and classified as moderate. Despite the lack

of systematicity and completeness of the surveyed

data items, our data provide a solid baseline for the

understanding of arachnidism in the Interior Atlantic

Rainforest and possible accident prevention

measures, being information of crucial importance for

the regional health system.

We hypothesize that our analysis may have

overestimated the proportion of cases of phoneutrism

due to differential diagnostic sensitivity. The diagnosis

of phoneutrism is of greater sensitivity due to its

characteristics (acute intense pain, imprint of the fangs,

size of the animal; usually the victim brought the spider

involved). While in cases of loxoscelism, access to

etiological diagnosis is less sensitive due to the

characteristics of the accident (low pain bite, very small

animal, and patients generally do not bring the spider to

the doctor's office not allowing expert determination).

Taxonomic diagnosis makes it possible to dismiss the

diversity of possible differential diagnoses that

generate inconsistency in defining the etiology

(Suchard, 2011; du Plesis and Reuter, 2021), otherwise

diagnosis of loxoscelism can only be presumptive.

Recent studies indicate that accident records did not

correspond to the geographical distribution of the

arachnid (Azevedo, Azevedo, Ramalho, Goldoni and

Brescovit, 2017) and that only 22% of 134 case

analysis publications met the toxicological evidence

required for the diagnosis of spider bites: a) clinical

effects at the time of the bite, b) capture of the spider

and c) expert identification of the species (Stuber and

Nentwig, 2016; Peigneur, Limab and Tytgata, 2018).

The high incidence of phoneutrism in the study area

can be explained by the abundance of this species,

associated with jungle environment, and the

unintentional risky habits of the local population

sharing its habitat. In contrast, the low involvement in

accidents of Lo. hirsuta may be related to its docility

and reserved habits, despite being frequently

synanthropic, although under-reporting of cases is also

possible. The profile of arachneism in northern

Misiones differs from that found in the rest of the

country, being similar to that observed in the Forest's

landscapes in the south of Brazil. Given the presence

of shared jungle habitats in the study area, these

results should not be surprising. The presence of large

urban centers in Brazil, in contrast to small cities in a

jungle matrix in Misiones, may explain the

preeminence of accidents with Loxosceles spp.

(synanthropic) over cases involving species of the

genus Phoneutria (wild) (Santana et al., 2020;

Benedet, Brocco- Bertan, Zorzan and Tessaro, 2021).

The habits and lifestyles of the local population,

influenced by a low perception of risk of arachnidism

during interaction with spiders, may explain 1) that

most of the accidents occurred during the day, when

spider are mostly inactive, 2) that the bites are mainly

on hands and feet, and 3) that the accidents occur

during normal household or rural duties.

Unlike most invasive scorpions of genera Tityus in

Bol. Soc. Zool. Uruguay (2ª época). 2024. ISSN 2393-6940Vol. 33 (1): e33.1.4

LÓPEZ Y COUTO

the study area (López, 2021), medically important

spiders are native and frequently observed species.

The conservation of native populations prevents the

invasion of exotic species, while anthropogenic

modifications of natural environments generate new

environments potentially suitable for the invasion of

arachnid species and zoonotic vectors (Taucare-Ríos,

Brescovit and Canals 2013; Keesing and Ostfeld,

2021). The three genera of spiders of medical

importance in South America are characterized by the

constant expansion of their distribution, mainly by

anthropochory (Vetter and Hillebrecht, 2008; Caruso,

Lauria, de Souza, Casais-e-Silva and Zingali, 2021).

The importance of spiders also lies in their

Bol. Soc. Zool. Uruguay (2ª época). 2024. ISSN 2393-6940Vol. 33 (1): e33.1.4

Spider bites in the Argentinian Atlantic Forest (2017-2023)

Fig. 7: A: Loxosceles hirsuta (♀). B: L. hirsuta (♂). C: After ecdisis, hairs of the cephalic region are evident, further back the radial

lines of hairs of the fovea and the three pairs of black eyes forming a "V". D: Copula. E: Care of the egg sac with the clutch. F:

Female and newly hatched nymphs. Scale bars: 1 cm. Laboratory photographs: CAL.

ecosystemic roles as predators and prey of

invertebrates and vertebrates (Foelix, 2011;

Gualteieri, 2015). Arachnids use their venom primarily

for prey capture and secondarily for defense, the

expenditure of valuable amounts of venom in

incidents with humans responds to a perceived threat

by the animal, which triggers a defense action (Foelix,

2011). On the other hand, spider venoms can be a

source of molecules with different applications in

research and health (Peigneur, Limab and Tytgata,

2018; Wu et al., 2019).

Chemical control (insecticides/arachnicides and

repellents) is an inadequate spider control strategy,

since these compounds have a negative impact on

native spider populations and the surrounding

biodiversity (Ramires and Silva, 2011). On the other

hand, the repellents are mostly ineffective (Isbister

and Fan, 2011). The use of ant semiochemicals can

provide a new effective and innocuous strategy for

synanthropic spider species control (Fischer, Lee,

Dong and Gries, 2021).

The environmental education, oriented to the

adoption of human appropriate behaviors and habits,

such as the dissemination of practical measures and

ecological characteristics of local poisonous species,

seems to be one of the best tools for low-risk

coexistence (Malhotra et al., 2021). Basic preventive

measures can be effective to mitigate spider bites in the

region, as well as the prevention of scorpionism,

ophidism and the proliferation of vectors (mosquitoes

and phlebotomines). Among them we can recommend

for 1) Outdoor environments: in gardens, keep grass

short; maintain a correct management of organic

waste; remove accumulation of any material; when

walking, always wear closed footwear, and use

flashlights at night. During rural tasks, wear high closed

footwear and leather gloves. 2) In the residence: seal

cracks in walls and floors; close all openings with

mosquito netting, as well as external and internal

drains; add skirting boards on doors that do not allow

the passage of arachnids. 3) Indoors: do not

accumulate objects; regularly clean floors and places

with no movement such as furniture or storage rooms

using gloves; do not walk barefoot; shake all clothing

that is going to be used; check the bed before going to

sleep; and do not sleep on the floor. Either way,

maintain constant vigilance, especially at times of

activity of the species of medical interest: at night and in

hot weather.

It is important to highlight that the National Institute

of Biological Production produces antivenoms for the

poisonous species present in the country, the treatment

is completely free of charge in the public health system.

CONCLUSIONS

Spider bites in the Argentinian Interior Atlantic

Rainforest are produced by native species, frequent in

these landscapes, and facilitated by the low human

perception of risk. It is important to promote the

implementation of taxonomy services linked to health

system for: monitoring the composition of spider

assemblages of medical interest, contribution in the

training and updating of health personnel and

environmental education programs and reach a

taxonomic diagnosis in cases of animal poisonings.

The health system should improve the systematic

registration of accidents, from the admission of the

bitten person, to the identification of the spider species,

to the follow-up of possible sequelae.

ACKNOWLEDGEMENTS

Andrea Gularte and Luis Cavagnaro(†). Ana

Munévar for critical reading of the manuscript. Dario

Lirussi for the critical reading and correction of the

English version of the original draft. Quenia de los

Santos, for the design of the images. To the anonymous

reviewers of the journal.

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