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Grass snakes (Natrix natrix sensu lato) are semi-
aquatic snakes distributed from northern Africa through
most of Europe to Central Asia (Sindaco et al., 2013;
Geniez, 2018; Zaher et al., 2019; Asztalos et al.,
2021). They are currently classied into three different
parapatric species: the Common or Eastern Grass Snake,
N. natrix (Linnaeus, 1758), the Barred Grass Snake, N.
helvetica (Lacépède, 1789), and the Red-eyed or Iberian
Grass Snake, N. astreptophora (Seoane, 1884) (Pokrant
et al., 2016; Kindler et al., 2017; Schultze et al., 2020;
Speybroeck et al., 2020). Natrix helvetica is composed
of several subspecies (see Fritz and Schmidtler, 2020),
including the Italian Barred Grass Snake, N. h. sicula
(Cuvier, 1829), which occurs in mainland Italy (except
in the northeastern portion), Sicily, Elba, and southern
Switzerland (Fritz and Schmidtler, 2020; Schultze et al.,
2020; Di Nicola et al., 2021).
Grass snakes rarely deploy active defence (e.g., striking)
toward humans, and they are considered non-venomous
and mostly harmless (e.g., Bruno and Maugeri, 1990;
Kreiner, 2007; Pokrant et al., 2017; Geniez, 2018).
When threatened, they usually try to ee, but if they
are cornered or manipulated, their antipredator response
may include death feigning (often belly-up with mouth
open, tongue hanging out and, sometimes, bleeding from
the mouth), emission of foul-smelling cloacal secretions,
hissing, attening of the neck to appear larger, strikes
with the mouth closed, a “cobra stance”, and rarely
reported tail vibrations (see Bruno and Maugeri, 1990;
Eckstein, 1993; Arnold and Ovenden, 2002; Ushakov,
2006; Gregory et al., 2007; Kreiner, 2007; Scali et al.,
2011; Kwet, 2016; Speybroeck et al., 2016; Pokrant et
al., 2017; Geniez, 2018; Paterna, 2019).
A bite is a rare event in grass snakes (e.g., Boulenger,
1912; Arnold and Ovenden, 2002; Kreiner, 2007; Scali et
al., 2011; Speybroeck et al., 2016; Di Nicola et al., 2021).
Two clinical reports of (supposed) grass snake bites exist:
one from the UK, where a patient had clinical signs
after being bitten by an “unusual snake”, subsequently
identied as a European Grass Snake (Gardner-Thorpe,
1967); and one from Poland, which was traced back to a
grass snake only with the oral testimony of the seventeen-
year-old bitten patient (Satora, 2004). In both cases,
however, it is not known specically what snake species
may have been responsible for the interaction. Moreover,
in captive grass snakes Gläßer-Trobisch and Trobisch
(2008) reported two N. helvetica females striking at the
breeder’s index and middle ngers while competing for
food. In the image provided in that paper, each snake
seems to try to swallow a nger. However, such a case
cannot be considered in evaluating the behaviour of wild
grass snakes. To our knowledge, any biting behaviour
of wild grass snakes towards humans has never been
documented in the scientic literature. Here we report
two different episodes of defensive biting behaviour in
Italian Barred Grass Snakes, both observed in Sicily, Italy.
The rst incident occurred on 28 September 2018
during a zoological survey in Ucria Municipality, Messina
Province, Italy (38.0370°N, 14.8919°E; elevation 830
m), when two of the authors (RC and MLV) observed an
adult female N. h. sicula (estimated total length 120 cm)
basking partially shaded in the undergrowth next to a dirt
path (10:57 h, cloudy weather, temperature 11–17°C). The
grass snake, which was nearing its moulting time, was not
Herpetology Notes, volume 16: 229-232 (2023) (published online on 27 March 2023)
First documented cases of defensive biting behaviour
towards humans by the Italian Barred Grass Snake,
Natrix helvetica sicula (Cuvier, 1829)
Matteo Riccardo Di Nicola1,*, Roberto Chiara2, Sebastian Colnaghi3, Mario Lo Valvo4,
and Francesco Paolo Faraone4
1 Unit of Dermatology, IRCCS San Raffaele Hospital,
Via Olgettina 60, 20132 Milan, Italy; and Asociación
Herpetológica Española, Apartado de Correos 191, 28911
Leganés, Madrid, Spain.
2 Department of Ecology, Faculty of Environmental Sciences,
Czech University of Life Sciences, Kamýcká 129, 165 00
Praha, Suchdol, Czech Republic.
3 Viale Epipoli, 96100 Siracusa, Italy.
4 Dipartimento Scienze e Tecnologie Biologiche, Chimiche e
Farmaceutiche, University of Palermo, Via Archira 18, 90123
Palermo, Italy.
* Corresponding author. Email: dinicola.matteo@hsr.it
© 2023 by Herpetology Notes. Open Access by CC BY-NC-ND 4.0.
Matteo Riccardo Di Nicola et al.
230
particularly responsive to our approach and did not try to
escape, possibly also due to the relatively low ambient
temperature and absence of direct sunlight. Placing
ourselves on either side of the snake allowed it to remain
still on the ground for photography and made capture
unnecessary. However, the snake hissed loudly during our
activity around it, and when one of the authors brought
a smartphone close to its head in order to document its
hissing behaviour, the snake struck repeatedly, although
not as rapidly as one might expect from a snake on a
warmer day. In ve out of six strikes, the mouth was open
(video clip: https://youtu.be/x8wN6licsBY; Fig. 1A, B).
One of the strikes hit the hand but caused only a slight
scratch without any other clinical signs. The snake was
left in place after the video recording.
The second observation occurred on 29 May 2022,
during a herpetological survey in Sortino Municipality,
Syracuse Province (37.1275°N, 14.9722°E; elevation
520 m), when three of the authors (MRDN, SC, and
FPF) observed an adult female N. h. sicula (estimated
total length 98 cm) basking in the shade of the vegetation
in a dry rainwater collection channel alongside a dirt path
(14:30 h, slightly cloudy weather, temperature 17–28°C).
The snake was caught by hand and immediately delivered
a quick bite with the mouth slightly open. Further bites
were received during handling for photography. The
behaviour was again lmed and photographed with
a smartphone. The animal was placed on the ground
and every time the authors approached with a hand or
touched the snake, it reacted with quick strikes, almost
all characterised by small and effective bites with
the mouth slightly open (video clip: https://youtu.be/
aUumcqxixNQ; Fig. 1C, D). After having lmed six
bites (out of seven strikes), the snake gradually reduced
the frequency of strikes, and late strikes occurred with the
mouth closed. The snake was then released at the place
of capture. Unlike the individual from the rst case, this
grass snake was not about to moult and appeared very
responsive and quick in its movements.
One of the bites from the second grass snake caused a
Figure 1. (A, B) First adult female Natrix helvetica sicula striking with an open mouth. (C, D) Second adult female N. h. sicula
biting an author’s hand. Slight bleeding is visible at the base of the thumb following a previous bite. Frames were taken from a
video clip.
small puncture wound followed by light bleeding (Fig.1C,
D), which resolved spontaneously after a few minutes and
was not followed by any other clinical signs or symptoms.
In the case of the captive bites mentioned above (Gläßer-
Trobisch and Trobisch, 2008), acute swelling and
discolouration of the hand, without pain, were reported.
However, these isolated episodes are insufcient to
evaluate the possible consequences of such bites.
Natrix natrix sensu lato are aglyphous snakes (Petrilla
et al., 2008; see Berkovitz and Shellis, 2017: Fig 7.36,
for lateral and ventral views of the dentition). In grass
snakes, presence and function of oral glands secreting
toxic substances are still under debate. Old studies
provided conicting results: whereas Phisalix (1922)
reported the presence of Duvernoy’s glands, Smith and
Bellairs (1947) reported the absence of these glands
in the taxon (see also Taub, 1967; Weinstein, 2011).
Investigations using anatomical, physiological, and
molecular approaches should be conducted to deepen
our knowledge of oral glands and related secretions
for N. natrix sensu lato. Future cases of bites could be
interesting to study their clinical effects in humans.
Regarding the defensive biting behaviour towards
humans, all authors are used to manipulating N. helvetica
individuals and, in some cases, have witnessed strikes
with a closed mouth accompanied by hissing, but none
have never received a bite. Specically, for Sicilian
populations, one of the authors (FPF) manipulated 242
individuals for biometric data collection (55 males, 115
females, 60 juveniles, 12 of undetermined sex) during
2000–2016 and received no bites. Sporadic reports of
bites from citizen science observations are available but
in the absence of documentary evidence, cases of death
feigning (thanatosis) cannot be excluded in which the
snake, with its mouth open, indirectly caused contact
between its teeth and a person’s skin. Considering
that grass snakes are among the most frequently
encountered and studied snakes in their range, the lack
of documentation on defensive biting behaviour towards
humans appears to conrm its actual rarity. Further
investigations should be conducted in this regard also
to better understand the antipredator behaviours of this
species complex.
Acknowledgements. We thank Anna Cerullo for a pre-
review of the manuscript. Snakes were handled following
ministerial and regional permits (MATTM Prot. n. 2766/T-A31,
12/01/2018 and Regione Siciliana Prot. n. 1637, 24/01/2018;
MATTM reg. 0039049, 15/04/2021 and Prot. ISPRA 10201,
24/03/2021; MATTM reg. 0024526, 28/02/2022 and Prot. ISPRA
009384/2022, 23/02/2022).
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Accepted by Arnaud Badiane
... Natrix natrix s.l. are aglyphous snakes [107] and the presence of oral glands secreting toxins is still under debate (See [108]). In this regard, studies addressing the Sardinian grass snake are totally lacking. ...
... obs.). Although very rare, cases of N. helvetica biting humans exist [108], but to date, they have never been reported for N. h. cetti. ...
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