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| Adult male Grass snake (Natrix natrix, “persa” morph), head detail (Picture: Plato Stefanopoulos) |
Introduction
The
grass snake (Natrix natrix) is a medium-sized Natricine snake known
mainly for its association with freshwater and its extremely variable
appearance. Its scientific name, Natrix, is derived from the Latin “natare”, meaning swim, therefore "Natrix" is the female form of "swimmer". The name is very much deserved as the
snake is an excellent swimmer. It has a vast distribution in the palearctic,
ranging all the way from Germany to as far East as lake Baikal in Eastern
Russia. It occurs as far north as Norway and Finland and as far south as
Northern Iran and Cyprus. The binomial name Natrix natrix used
to apply to populations west of Germany, most of Italy, the UK and the Iberian
peninsula, however, after molecular research, the taxon was split into three
distinct species, with Iberian populations being classified under Natrix
astreptophora, and UK and Western Europe populations under Natrix
helvetica, with all other populations keeping the binomial name Natrix
natrix. All that paired with hybridization, back-crossing and
inconsistent phenotypic variation across its range in the mainland have rendered the
taxonomy of Natrix natrix a topic of vigorous
debate among herpetologists. Even more recent phylogenetic data challenges the
subspecies status of several morphologically distinct populations listed as
subspecies in the mainland and several islands, leaving room for extensive
taxonomic change in the future.
Description
Natrix natrix possesses a functional Duvernoy's gland (as do all members of the genus Natrix) and their saliva has been shown to be deadly to amphibians. Their bite, however, is harmless to humans. Usually has 19 rows of dorsal scales, which are keeled. Sexually dimorphic – females larger
and more robust than males. Males usually up to 80 cm TL, females usually up to
120 cm TL, with exceptional individuals pushing 200 cm TL. Insular populations
such as those in the Cyclades are significantly smaller. Coloration and pattern
extremely variable and can vary both within the same locality as well as from
one locality to another. The most common morph in Greece that can be found in
the mainland and on several islands is the “persa” morph, with the
background color ranging from gray, to brown, to olive, to yellowish/golden
brown, with regular black bars/blotches on the sides and top of the body, of
varying size and number, with a partial yellowish or buff collar around the neck,
followed by a more defined partial black collar. Usually with two buff or yellow
longitudinal stripes along either side of the dorsal area. Very defined black
bars between the labial scales. The belly is white or yellowish, with varying
amounts of semi-regular black blotches. Other morphs include erythristic, black
(charcoal) and axanthic versions of the persa phenotype.
Individuals of this morph lacking the characteristic stripes on the back
(stripeless) can also be found and even seem to be more prevalent than striped
individuals in some localities. Fully melanistic individuals occur, especially
in the Cyclades. Generally exhibits two types of melanism. Some melanistic
individuals have an overall dark coloration with traces of lateral and
sometimes even dorsal pattern (e.g. blotches or stripes) that gradually fades
to a typical ventral pattern. Other melanistic individuals are jet black
(including the eyes) with light dots/patches/traces of pattern with a sharp
transition to the black background, dorsally and ventrally. Both types of melanism
also very frequently occur in the formally recognized subspecies N. n. fusca and N. n. schweizeri. Natrix
natrix schweizeri is phenotypically distinct from “persa”
individuals in lacking stripes and having more pronounced blotches on the
dorsal and lateral areas with higher contrast than mainland individuals.
Melanistic individuals are also common in N. n. schweizeri.
Intergrades (intermediate forms) between the recognized subspecies can be found
on some islands. Populations on some islands, e.g., from Kythera and perhaps
Thassos seem to be phenotypically distinct, lacking the persa stripes, being
almost reminiscent of Natrix tessellata, with an unusually high
number and density of dorsal and lateral blotches. Populations in South Aegean/Anatolian
islands often with a very pale background color and higher contrast. Insular
populations in general seem to yield the highest frequency of observations of
aberrant individuals. It is highly unlikely that any of the aforementioned
populations are genetically distinct enough to be taxonomically separated,
especially when considering that individuals with almost identical phenotypes
to the aberrant individuals in islands can also (though extremely rarely) be
observed in the mainland. It is seemingly impossible to describe every morph,
as the phenotypic variation of Natrix natrix seems endless.
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| Adult female, “persa” morph, Attica (C) Plato Stefanopoulos |
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| young male, "charcoal" morph, Attica (C) Plato Stefanopoulos |
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| Adult male, “persa” morph, Attica (C) Plato Stefanopoulos |
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Adult male, Attica. Note that grass snakes often appear brighter when underwater (C) Plato Stefanopoulos
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| Large adult female. Note the defensive head flattening as well as the very faint buff stripes and the unusually thick and prominent black blotches. Attica (C) Plato Stefanopoulos |
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Rescued adult female, "stripeless" morph, Euboea (C) Plato Stefanopoulos
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| Juvenile, Euboea (C) Stamatis Kalogiannis |
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| Adult male, Attica (C) Plato Stefanopoulos |
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Adult female, “charcoal” morph, partially retaining "persa" stripes, Kerkini (C) Stamatis Kalogiannis
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| Juvenile, "stripeless" morph, Rhodes (C) Alexandros Dounis |
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| Adult, Ioannina (C) Ioannis Gkourogiannis |
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| Adult male, Achaea (C) Plato Stefanopoulos |
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| Young male, charcoal morph, Attica (C) Plato Stefanopoulos |
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| Adult female, ''picturata'' morph, Serrai (C) Plato Stefanopoulos |
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| Juvenile, submontane Corinthia (C) Plato Stefanopoulos |
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| Adult female with spinal malformation, Nestos drainage (C) Plato Stefanopoulos |
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| Adult male, upper Rhodope piedmont (C) Plato Stefanopoulos |
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| Juvenile, reminiscent of Northern European individuals, Northern Evros (C) Plato Stefanopoulos |
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| Large adult female, Attica (C) Plato Stefanopoulos |
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| Adult female, Phocis, 1200 m asl (C) Plato Stefanopoulos |
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| Large female, ''picturata'' morph (C) Stamatis Kalogiannis |
Habitat
Can be found in and around all kinds of freshwater systems.
From ponds, to rivers, to lakes, to small streams, to swamps. Does not need
permanent water and can often inhabit areas around intermittent streams,
adopting a terrestrial lifestyle. Shows a strong preference for edge habitat,
meaning woodland or large, thick shrubs bordering open habitat such as a creek
bed, the edge of a pond or a forest clearing or even cultivated field. It will
often venture in gardens, cultivations, and other degraded environments. Some
urban populations in creeks. Phrygana habitats are inhabited by populations in
arid islands such as the Cyclades. It can be found from sea level, very often
in brackish environments, up to 2400 m asl.
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| Intermittent section of a perennial stream bordering cultivations – habitat of Natrix natrix |
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| Degraded urban stream – habitat of Natrix natrix |
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| River mouth of a perennial stream – habitat of Natrix natrix |
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| Severly degraded cultivations near an urban area, over 2.5 km from the nearest permanent water source – habitat of Natrix natrix |
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| Intermittent section of a perennial stream bordering pine forests – habitat of Natrix natrix |
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| Lowland reaches of a perennial stream bordering maquis shrubland and cultivations – habitat of Natrix natrix |
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| Eutrophic agricultural canal – habitat of Natrix natrix |
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| Artificial garden pond complex – habitat of Natrix natrix |
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| Intermittent stream supplied by agricultural activity – habitat of Natrix natrix |
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| Mountainous perennial stream bordering lush vegetation – habitat of Natrix natrix |
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| Flooded grassland next to a major river mouth – habitat of Natrix natrix |
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| Shore of a large lake – habitat of Natrix natrix |
Biology
The grass snake overwinters underground, but brumation can
be interrupted on warm winter days so that the snake can bask or even hunt. Nevertheless,
it does not seem to be very winter active, in early winter at the very least. Mating
occurs in early spring, where numerous males will form a pile on top of the
female as a result of competition to copulate, which is referred to as a mating
ball. Eggs are laid in late spring or early summer, and the clutch size can
range from 2 to 100 eggs, with 30 being the usual amount. The young hatch in
late summer, and measure approximately 20 cm TL, though Balkan populations are
known to be larger than northern ones. It matures in its third or fourth year
of age, and mature males can be as small as 55 cm long. Females have a faster
growth rate than males, and while males will effectively stop growing beyond
the 80 cm TL mark, females can become much larger in the same amount of time as
males, with individuals above 110 cm TL being common. The grass snake is very
well-suited for hunting in and around freshwater. It is a powerful swimmer, can
very competently dive underwater and hold its breath for extended periods of
time, and has a remarkable cold tolerance, with active, feeding individuals
having been observed in temperatures as low as 7 degrees Celsius. However, that
is an exceptionally rare occurrence, though it can reliably be found foraging
in the water on mostly cloudy spring days with the maximum temperature as low
as 17 C. It may also be found basking in the sunlight on dry logs or branches,
usually before becoming active in the water. It is both diurnal and nocturnal,
perhaps to almost equal extents. It can be found active anytime, anywhere,
given that the conditions allow activity to take place. It does not tolerate
extreme heat, though it can become active in weather too hot for other snakes
to withstand due to its ability to easily cool off in freshwater, which is
convenient due to its preferred prey, amphibians, also being there. The grass
snake is referred to by many as an amphibian specialist, with its prey in
mainland Greece being comprised almost exclusively of frogs, toads and their
larvae. It hunts its prey actively. It does not kill by
constriction and as a result, prey items are often swallowed alive, with the toxic saliva probably serving to weaken the prey.
The meal size is often very large in comparison to the snake, forming an
obvious food bolus upon being swallowed. In such cases, movement is impaired,
and the snake will stay hidden and often place the part of its body where the
digested meal is on a heat source to aid in digestion. It is immune to the
toxins of the common toad Bufo bufo and the green toad Bufotes
viridis, both of which are very commonly taken. Pelophylax sp.
are also a preferred prey item. Fish form a small part of the snake’s diet as
well. Nevertheless, Natrix natrix is by no means exclusively
semi-aquatic. A permanent body of water is not necessary for a population to
exist, and a vernal pool that supports the existence of toads in an otherwise
dry area will often suffice. The snakes will often venture out up to several
kilometers from any water source in search of food or new habitat and are very
adaptable, with populations in arid areas, such as those in the Cycladic
islands, being known to mostly prey on lizards and small mammals, with
invertebrates as well as small birds being consumed in extreme cases. Even so,
it generally seems that grass snakes need amphibians to sustain a population and
this could perhaps be attributed to the fact that other species, specialized in
terrestrial prey may outcompete them. The grass snake is also notorious
for its plethora of defensive behaviors – if caught, it will very rarely bite (less than 1% chance according to our observations), most
often resorting to emitting a foul-smelling secretion from the anal glands
(musking), which it rubs on its whole body very efficiently. Other common defensive displays include hissing, inflating its body and widening its head, giving it a
triangular shape. It will sometimes strike without biting, hide its head in
coils of its body, and feign death (thanatosis), where it will remain
motionless, sometimes even flipping over on its back, occasionally with its mouth open, and
its tongue exposed. In the most extreme cases of thanatosis, auto-hemorrhaging (deliberate bleeding) from the lining of the mouth may occur. Perhaps its most remarkable defensive behavior is one where
the snake will rear up, flatten its neck and pretend to strike while trying to
get away from predators – this is interpreted as a cobra imitation by many,
which could mean it is a fossil behavior, persisting long after the extinction
of the Mediterranean cobras (Naja romani), the range of which largely
overlapped with species in the Natrix natrix complex in the
Miocene. That being said, our opinion is that it is likely that this behavior immitates that of Eurasian vipers, which can assume very similar defensive posturing to that of large grass snakes.
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Adult male, “persa” morph, found over 2.5 km away from the nearest permanent water source. Attica (C) Plato Stefanopoulos | | Young female with aberrant coloration. Death-feigning behavior is shown on the right. Achaea (C) Plato Stefanopoulos |
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Top left: exaggerated death-feigning
Top right: autohemorrhaging
middle right: head flattening
bottom row: rearing, neck flattening and striking |
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| Adult male, nearing the end of a shed cycle |
Distribution
Rather widespread snake, generally associated with the presence of waterbodies and amphibians, although it has even be found on small and dry Aegean islands (e.g. Tigani islet, Cyclades archipelago). It occurs in all of the mainland and on several islands such as Euboea, Corfu, Kefallonia, Lefkada, Zakynthos, Skyros, possibly Skiathos, Thasos, Samothrace, Limnos, Lesvos, Chios, Samos, many of the Cyclades islands (e.g. Milos, Kimolos, Tinos, Andros, Paros, Naxos) and the Dodecanese (Rhodes, Kos, Leros, Karpathos, Kasos).
The taxonomic status of the species has been subject to taxonomic revisions and remains largely unresolved. Many have doubted the validity of the previously widely recognised subspecific taxa in Greece (N. n. persa, N. n. fusca, N. n. schweizeri). A recent phylogenetic study by Asztalos et al. (2021) proposed a new taxonomic resolution for grass snakes, classifying all Greek populations as a single subspecies (N. n. moreotica), with a potential contact zone between N. n. moreotica and N. n. vulgaris in NW Greece. Despite this, however, the species displays seemingly enormous phenotypic variability within the country.
Described subspecies & local variations:
- Natrix natrix persa (Pallas, 1814): Mainland, Peloponnese, Euboea, Ionian islands, most Aegean islands – perhaps a widespread 'striped morph' rather than a valid subspecies
- Natrix natrix fusca Cattaneo, 1990: Kea island
- Natrix natrix schweizeri (Pallas, 1774): Milos, Kimolos, Polyaigos
- Intergrade zones between N. n. schweizeri and N. n. persa are reported from the Cyclades and from Skyros
- Stripeless and various other aberrant morphs in populations currently assigned to 'persa' are very frequent in South Euboea, Rhodes, Kythera, Karpathos, Samos and other islands
- Natrix natrix moreotica (Bedriaga, 1882): All of Greece
- Natrix natrix vulgaris (Laurenti, 1768): Northernmost parts of NW Greece
As the taxonomy of Natrix natrix is still complicated and unresolved, we do not include subspecies in the distribution map.
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| Distribution of Natrix natrix in Greece |
