Boletín de la Sociedad Zoológica del Uruguay, 2024
Vol. 33 (1): e33.1.4
ISSN 2393-6940
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
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.
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,
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
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:
Fecha de recepción: 28 de diciembre de 2023
Fecha de aceptación: 01 de junio de 2024
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.
We conducted a descriptive observational study
based on the records between 2017 to 2023 of the
Taxonomy Service (TS) of the National Institute of
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: The occurrence of the
Bol. Soc. Zool. Uruguay (2ª época). 2024. ISSN 2393-6940Vol. 33 (1): e33.1.4
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.
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
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.
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.
(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