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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:
© 2023 by Herpetology Notes. Open Access by CC BY-NC-ND 4.0.
Matteo Riccardo Di Nicola et al.
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:; 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:
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
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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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The Sardinian grass snake, Natrix helvetica cetti, is an endangered endemic snake subspecies with a restricted and highly fragmented geographic distribution. Information on its ecology and detailed geographic distribution are scarce and may negatively impact on its conservation status. Therefore, a literature review on its taxonomy, morphology, ecology, and conservation is presented here. Moreover, field records from the authors, citizen science and the existing literature provide an updated geographic distribution highlighting its presence within 13 new and 7 historic 10 × 10 km cells. Bioclimatic niche modelling was then applied to explore patterns of habitat suitability and phenotypic variation within N. h. cetti. The geographic distribution of the species was found to be positively correlated with altitude and precipitation values, whereas temperature showed a negative correlation. Taken together, these outcomes may explain the snake’s presence, particularly in eastern Sardinia. In addition, analysis of distribution overlap with the competing viperine snake (N. maura) and the urodeles as possible overlooked trophic resources (Speleomantes spp. and Euproctus platycephalus) showed overlaps of 66% and 79%, respectively. Finally, geographical or bioclimatic correlations did not explain phenotypic variation patterns observed in this highly polymorphic taxon. Perspectives on future research to investigate N. h. cetti’s decline and support effective conservation measures are discussed.
... The presence of small venom glands (typically referred to as Duvernoy's glands) is known in several European rear-fanged colubrids [60][61][62][63][64][65][66]. Among these, members of the genera Macroprotodon (distribution in Europe: Iberian Peninsula, Balearic Islands and Lampedusa) and Telescopus (distribution in Europe: Balkan peninsula, Greece, Cyprus, Malta, northeastern Italy) [26,28] are only rarely reported to cause mild, local symptoms (e.g., swelling, erythema, pain) following their bites, and will therefore not be discussed in detail. ...
... The presence of small venom glands (typically referred to as Duvernoy s glands) is known in several European rear-fanged colubrids [60][61][62][63][64][65][66]. Among these, members of the genera Macroprotodon (distribution in Europe: Iberian Peninsula, Balearic Islands and Lampedusa) and Telescopus (distribution in Europe: Balkan peninsula, Greece, Cyprus, Malta, northeastern Italy) [26,28] are only rarely reported to cause mild, local symptoms (e.g., swelling, erythema, pain) following their bites, and will therefore not be discussed in detail. ...
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Europe presents a high number of venomous and poisonous animals able to elicit medically relevant symptoms in humans. However, since most of the accidents involving venomous or poisonous animals in Europe are unreported, their incidence and morbidity are severely overlooked. Here we provide an overview of the European vertebrate species of greatest toxicological interest, the clinical manifestations their toxins can cause, and their treatment. We report the clinical symptoms induced by envenomations and poisoning caused by reptiles, fishes, amphibians and mammals in Europe, ranging from mild, local symptoms (e.g., erythema, edema) to systemic and potentially deadly. The present work constitutes a tool for physicians to recognize envenomation/poisoning symptoms caused by the most medically relevant European vertebrates and to decide which approach is the most appropriate to treat them.
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Based on 1031 samples of grass snakes from Central Europe, we examine the recently reported occurrence of the southern subspecies of the barred grass snake (Natrix helvetica sicula) in southern Bavaria, Germany. Using 13 microsatellite loci and mtDNA coding for the cytb gene and the partial ND4 gene plus adjacent tRNAs, we show that N. h. sicula is restricted to a few river valleys (Inn, Isar, Loisach) in southern-most Bavaria and adjacent Tyrol, Austria. At the widening of the river valleys into the pre-Alpine plains, N. h. sicula hybridizes locally with the common grass snake (Natrix natrix) in a bimodal hybrid zone. Our study provides evidence that Central Europe was colonized by Natrix helvetica over two distinct immigration routes. In addition to the previously known western route of the nominotypical subspecies, leading to the colonization of the Rhine region, N. h. sicula crossed the Alps, most likely using the Brenner Pass and/or the Reschen Pass. Our study underlines that the Alps are not an impermeable biogeographic barrier, as often assumed. North of the Alps, the combination of geographic setting (occurrence of N. h. sicula in sheltered Alpine valleys) and population-density-dependent blocking of immigrants by the resident species (N. na-trix), acting in concert with intrinsic genetic factors, prevented the formation of a geographically more extended hybrid zone. Unlike N. helvetica, the two subspecies of N. natrix hybridize north of the Alps broadly, in accordance with their better genetic compatibility. Many populations of the resident Central European subspecies (Natrix natrix natrix) have been "genetically swamped" by Natrix natrix vulgaris immigrating from the Balkans. This led to the complete replacement of N. n. natrix by N. n. vul-garis in some regions, where today only the mtDNA of the nominotypical subspecies persists.
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Mimicking venomous species is widespread among animals, especially snakes. This concerns both visual and behavioral mimicry. Raising the forepart of the body and flattening the neck are characteristic defense behaviors of cobras and mimicked by several non-venomous snake species that co-occur with them. Here we describe the cobra stance for grass snakes (Natrix natrix complex), whose distribution range is largely allopatric to any living cobra species. Among the various defensive behaviors of grass snakes, the cobra stance is uncommon and rarely reported, which raises the questions how effective it is and why it evolved. The fossil record indicates that cobras and grass snakes were abundant and widespread across Europe during the Miocene, where they inhabited the same habitats. They continued to be sympatric in the Mediterranean region until the Pliocene, and in the eastern Mediterranean perhaps until the Middle Pleistocene. Thus, we hypothesize that the cobra stance represents a 'fossil behavior', which developed when the distribution ranges of grass snakes and cobras broadly overlapped. The absence of cobras in most of the extant distribution range of grass snakes, and hence unfamiliarity of typical predators with these dangerously venomous snakes since the Plio-/Pleistocene, explains its rarity nowadays because displaying the cobra stance is no longer advantageous. Migrating birds from Africa, however, may still serve to some extent as target species for the cobra stance in grass snakes, supporting its survival.
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Recent studies found major conflicts between traditional taxonomy and genetic differentiation of grass snakes and identified previously unknown secondary contact zones. Until now, little is known about gene flow across these contact zones. Using two mitochondrial markers and 13 microsatellite loci, we examined two contact zones. One, largely corresponding to the Rhine region, involves the western subspecies Natrix natrix helvetica and the eastern subspecies N. n. natrix, whereas in the other, more easterly, contact zone two lineages meet that are currently identified with N. n. natrix and N. n. persa. This second contact zone runs across Central Europe to the southern Balkans. Our analyses reveal that the western contact zone is narrow, with parapatrically distributed mitochondrial lineages and limited, largely unidirectional nuclear gene flow. In contrast, the eastern contact zone is very wide, with massive nuclear admixture and broadly overlapping mitochondrial lineages. In combination with additional lines of evidence (morphology, phylogeny, divergence times), we conclude that these differences reflect different stages in the speciation process and that Natrix helvetica should be regarded as a distinct species. We suggest a nomenclatural framework for presently recognized grass snake taxa and highlight the need for reconciling the conflicts between genetics and taxonomy.
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The grass snake (Natrix natrix) is Europe's most widely distributed and, in many regions, most common snake species, with many morphologically defined subspecies. Yet, the taxonomy of grass snakes is relatively little studied and recent work has shown major conflicts between morphologically defined subspecies and phylogeographical differentiation. Using external morphology, osteological characters, and information from 13 microsatellite loci and two mitochondrial markers, we examine differentiation of the subspecies N. n. astreptophora from the North African Maghreb region, the Iberian Peninsula and neighbouring France. According to previous studies, N. n. astreptophora corresponds to a deeply divergent mitochondrial clade and constitutes the sister taxon of all remaining grass snakes. In the French Pyrenees region, there is a contact zone of N. n. astreptophora with another subspecies, N. n. helvetica. Our analyses of microsatellites and mitochondrial DNA reveal that the distribution ranges of the two taxa abut there, but both hybridize only exceptionally. Even though many morphological characters are highly variable and homoplastic in grass snakes, N. n. astreptophora differs consistently from all other grass snakes by its reddish iris coloration and in having significantly fewer ventral scales and another skull morphology. Considering further the virtual absence of gene flow between N. n. astreptophora and N. n. helvetica, and acknowledging the morphological distinctiveness of N. n. astreptophora and its sister group relationship to all remaining subspecies of grass snakes, we conclude that Natrix astreptophora (Seoane, 1884) should be recognized as a distinct species. Further research is needed to explore whether N. astreptophora is polytypic because a single sample of N. astreptophora from Tunisia turned out to be genetically highly distinct from its European conspecifics.
This book is the first significant contribution to thoroughly examine the potential hazards associated with snakes of the former family, Colubridae. This family contained >65% of living snake species (approximately 3,000 taxa) and has recently been split into multiple families. Many of these snakes produce oral secretions that contain toxins and other biologically-active substances. A large variety of these snakes figure in the pet industry, yet little documented information or formal study of their potential medical importance has been published. Therefore, although the possible medical importance of many of these species has been subjected to speculation since the mid-nineteenth century, there is a limited amount of useful descriptive information regarding the real hazard (or lack thereof) of snakes belonging to this diverse, artificial family. There is a need for "one-stop shopping" offering information regarding their possible toxicity and clinical relevance as well as recommendations for medical management of their bites. This book is the first synthesis of this information and includes evidence-based risk assessment, hazard rankings and specific recommendations regarding important species, many common in captivity. Fills a gap in the toxinological, medical and herpetological literature by providing a comprehensive review of this entire assemblage of snakes, with particular attention given to their capacity, real or rumored, to cause harm to humans A patient-centered, evidence-based approach is applied to analyzing documented case reports of bites inflicted by approximately 100 species. Clinical management of medically significant bites from non-front-fanged colubroids is methodically reviewed, and specific recommendations are provided.