Hooding in the dice snake Natrix tessellata may backdate the origin of such behaviour in the genus Natrix

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Hooding is a very well-known defensive display of snakes,
the snake raises its head and the anterior part of the body
from the ground, and the neck is dorsoventrally compressed
by lateral expansion of the cervical ribs (Greene, 1979; Young
et al., 2010). This aposemac signal is intended to inmidate
potenal predators or threats, and has been made famous in
popular culture by cobras (family Elapidae) although its use
is not restricted to elapid snakes (Pope, 1935; Gharpurey,
1954; Greene, 1979). Among others, it has been recorded
in three natricid snakes of the genus Natrix: Natrix natrix,
Natrix helveca and Natrix astreptophora (Kabisch, 1978;
Pokrant et al., 2017; Paterna, 2019). In 2017, Pokrant et
al. concluded that this defensive mechanism is a ‘fossil’
behaviour, inherited by the grass snakes from an ancestor
that lived in Europe unl the Miocene–Plio-Pleistocene,
which had evolved hooding as Batesian mimicry of sympatric
elapids. Besides apparently sharing this defensive display
with cobras, Natrix species also visually imitate sympatric
viperids in both dorsal paern, defensive behaviour and by
head triangulaon (Valkonen et al., 2011; Paterna, 2019).
In this study we describe hooding in two dice snakes
Natrix tessellata (Lauren, 1768). The rst observaon
was on 3 May 2006 along the Chien river, in the locality
of Bistocco di Camerino, in the Marche region, Italy, where
there is a well-established populaon of dice snakes. On
this occasion, a specimen of a total length of about 105
cm, raised its neck and spread a hood while the posterior
poron of its body was being held by one hand (Fig. 1A &
B). This performance lasted long enough for the snake to be
photographed from several dierent angles. The maximum
width reached by the lateral expansion of the neck was
approximately equal to the length of the specimen’s head,
and stretching of the neck revealed dark-pigmented skin
between the dorsal scales. This manoeuvre also accentuates
the head triangulaon of the specimen, in a similar manner
to that observed in congeneric and sympatric N. helveca
(Paterna, 2019). The second episode occurred on 1 April
2008 in the Colorito swamp, in the province of Foligno, also
in the Marche region, where on the lakeside, a dice snake
displayed a hood (Fig. 1C & D) in a similar manner to the
previous observaon. Furthermore, in both cases the snakes
maintained the defensive display even aer their necks were
returned to the ground and they were in the process of
eeing (Fig. 1B & D). In both episodes there was a marked
dorsal plane variaon between vertebrae and ribs (Fig.
1A & C), i.e. the neck didn’t appear completely aened
dorsally as the vertebrae were more ‘elevated’ or ‘externally
pronounced’. Despite descripons of hooding in the grass
snakes being rare in literature, the externally pronounced
vertebrae does not seem to be so evident in the reported
case of N. helveca (Paterna, 2019), but clearly present in
N. astreptophora which is featured in many photographs on
online plaorms, to the extent that it seems that hooding
could even be frequent in this species.
It seems likely that hooding has a common evoluonary
origin in those four Natrix species that have been recorded
displaying it. The fact that such display has been observed in
N. tessellata, a sister taxon of N. astreptophora, N. helveca
and N. natrix, but has not been documented in the most
basal species Natrix maura, allows us to connect the origin
of this behaviour into a more precise me range between the
divergence of N. maura and the last common ancestor for
the remaining species. On the basis of recent phylogenec
studies, the development of such behaviour could be placed
in the early-middle Miocene (Guicking et al., 2006; Kindler
et al., 2018; Schöneberg et al., 2023). This is consistent with
the hypothesis that this defensive mechanism may have
been evolved as emulaon of sympatric elapids in central
Europe (Pokrant et al., 2017).
The oldest elapid fossils found in Europe belong to the
species Naja romani, of which there is an abundance
from the early German Miocene (Szyndlar & Schleich,
1993), middle French Miocene and late Austrian Miocene
(Szyndlar & Rage, 1990), to a second species, Naja iberica,
and indeterminate remains of a Naja sp. of which records
date back to the middle–late Spanish Miocene (Szyndlar,
1985; Villa et al., 2024). To date, the known European
fossil records of the genus Natrix from the mid–late
Miocene belong exclusively to exnct species, such as
Natrix sansaniensis from France (Rage, 1988; Rage & Auge,
1993; Ivanov, 2002), and Natrix longivertebrata in Austria
(Bachmayer & Szyndlar, 1985) and eastern Europe (Szyndlar,
1984, 1991), while fossils aributed to the contemporary
N. tessellata and N. natrix have origins no earlier than the
late Pliocene and Pleistocene (Markert, 1976; Zerova &
Chkjikvadze, 1984; Ivanon, 1999). However, the oldest fossil
records of the genus Natrix are restricted to central Europe,
and date back to the late Eocene and early Oligocene, with
Herpetological Bullen 171 (2025) 35
The Herpetological Bulletin 171, 2025: 35–37
Hooding in the dice snake Natrix tessellata may backdate the origin
of such behaviour in the genus Natrix
ALESSANDRO PATERNA1* & MARIO MARCONI2
1OPHIS Museo Paleontologico e Centro Erpetologico - 64100 Teramo, Italy
2Università di Camerino, Diparmento di Bioscienze e Medicina Veterinaria - 62032 Camerino, Italy
*Corresponding author e-mail: alessandro.paterna@hotmail.com
hps://doi.org/10.33256/hb171.3537
SHORT COMMUNICATION

36 Herpetological Bullen 171 (2025)
Alessandro Paterna & Mario Marconi
the species Natrix mlynarskii found in France (Rage, 1988;
Ivanov, 2001). It is therefore plausible that such defensive
mechanism has a central European origin, back-dated to
the ancestors of N. tessellata prior to the fragmentaon in
which ancestral populaons expanded eastwards, and from
which N. tessellata evolved in south-western Asia (Rögl &
Steininger, 1984; Guicking et al., 2006).
An alternave hypothesis on the origin of this defensive
display might not connect this phenomenon to the previous
coexistence in the same territory with cobras, but with
another defensive mechanism involved in the imitaon of
viperids. It is noteworthy how hooding in Natrix is linked
to head triangulaon and contributes to its denion and
extension through the lateral expansion of the rst cervical
ribs (Paterna, 2019). In this genus hooding seems to be
generally performed while raising the neck, while other
species of colubroids, e.g. Dasypels and Heterodon, usually
perform hooding with their neck and head close or parallel
to the ground. European viperids, in defensive posture raise
their heads from the ground and hiss loudly, while larger
allopatric viperids, such as Bis spp. and Crotalus spp., in
addion to this further triangulate their heads. It is of
interest that hooding has not been observed (yet?) in N.
maura, instead this species, as its common name ‘viperine
water snake’ suggests, is very well documented as a viper
mimic (Valkonen et al., 2011).
Figure 1. Adult dice snakes Natrix tessellata performing the hooding display - A. Specimen from river Chien hooding in erected posion, B.
Same specimen as A. hooding while its neck ascends to the ground, C. Specimen from the Colorito swamp hooding in erected posion, D.
Same specimen as C. hooding parallel to the ground.

Accepted: 20 September 2024
Herpetological Bullen 171 (2025) 37
Hooding in the dice snake Natrix tesellata may backdate the origin of such behaviour in the genus Natrix
Further invesgaon of hooding in natricids is required to
fully understand its funcon and origin. If hooding was to be
subsequently recorded in N. maura, the more ancient of the
species considered, then this would inuence the temporal
and spaal explanaons of its origin.
ACKNOWLEDGEMENTS
We thank Prof. Uwe Fritz for the reviewing the manuscript.
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