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Grass snake

Authors:
  • Caledonian Conservation Ltd

Abstract

Provides a description of grass snake (Natrix natrix) distribution, ecology and history in Scotland.
The Amphibians
& Reptiles of Scotland
Chris McInerny & Pete Minting
The production of this book has been supported
by the following organisations:
1
The Amphibians and Reptiles of Scotland
ii
Published 2016
by The Glasgow Natural History Society, Glasgow, Scotland.
Copyright © 2016 text, maps and charts by the authors
Copyright © 2016 photos by the respective photographers
Copyright © 2016 frontispiece illustration by Chris Rose
ISBN 978-0-9561126-8-2
A CIP catalogue record for this book is available from the British Library.
All rights reserved. No part of this publication may be reproduced or used in any form or
by any means - photographic, electronic or mechanical, including photocopying, recording,
taping or information storage and retrieval system - without permission of the publishers.
Cover photos:
Main image, female adder;
inserts from left, female slow-worm, common lizard and natterjack toad.
Typesetting and design by
Harry Scott (PicaDesign), 51 Charlton Crescent, Aboyne, Aberdeenshire AB34 5GN.
Email: picades@ifb.co.uk
Recommended citation:
McInerny CJ and Minting PJ (2016) The Amphibians and Reptiles of Scotland.
The Glasgow Natural History Society, Glasgow, Scotland.
iii
The Amphibians and
Reptiles of Scotland
Christopher J McInerny
(University of Glasgow)
Peter J Minting
(Amphibian and Reptile Conservation Trust)
Maps
Ian Andrews
Guest authors
Christopher Cathrine (Caledonian Conservation Ltd)
David O’Brien (Scottish Natural Heritage)
Frontispiece
Adder, Loch Lomond, March 2015 © Chris Rose
iv
A natterjack toad, the rarest native amphibian in Scotland. This species is restricted to coastal areas on
the Solway in the south-west of the country.
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The Amphibians and Reptiles of Scotland
Contents
Frontispiece i
Title iii
Contents v
Introduction 7
Acknowledgements 11
Species chapters
Amphibians
Common frog 14
Common toad 36
Natterjack toad 52
Palmate newt 72
Smooth newt 90
Great crested newt 102
Alpine newt 118
Reptiles
Adder 126
Grass snake 144
Slow-worm 158
Common lizard 174
Sand lizard 192
Leatherback sea turtle 206
Loggerhead sea turtle 222
Kemp’s ridley sea turtle 236
Green sea turtle 247
Bibliography 257
Appendices
A Site guide 285
B Legislation 289
C Useful websites 293
D Scientific names 295
E Sea turtle identification and strandings 299
F Habitat management case studies 303
G Exotic species 309
H Photographic credits 310
Index 312
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The Amphibians and Reptiles of Scotland
Identification
Adults and juveniles
The grass snake is the largest snake native to the UK. Females are usually larger than males,
measuring 80–100 cm in total length. The smaller males measure 70–80 cm. Occasionally,
larger specimens are recorded, including examples claimed to be up to 177.5 cm (Leighton
1901). Grass snakes are typically olive, green, brown or grey. A key identification feature is
the pale neck collar. This can be variable in colour being white, cream, yellow or even pale
orange, but is always pale, and bordered at the rear by two large black triangular markings.
The collar can appear to meet at the midline, but is broken. The underside of the snake is
highly variable, being chequered with white, grey and black to differing degrees. The pupil of
the eye is round, unlike the vertical pupil of the adder.
World range and taxonomy
Found throughout Europe, from the Iberian Peninsula, Britain and southern Italy to mid-Fennoscandia
and the Middle East; also present in north-west Africa. Up to nine subspecies recognised, with
N. n. helvetica native to England, Wales and possibly southern Scotland. Furthermore, there are thought
to be up to 15 distinct geographic forms in Europe.
Grass snake Natrix natrix
Ringed snake, water snake
Nathair feòir
Adult grass snake. The tongue is used to smell, to detect prey items, other snakes and predators. Note the
round eye pupil, distinctive from the vertical slit of the adder. All photos of grass snakes shown in this
chapter were taken in England.
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The Amphibians and Reptiles of Scotland
The subspecies N. n. helvetica is native to England and Wales, and may be the subspecies
seen in Scotland, although this cannot be confirmed without further study. N. n. helvetica is
typically olive-coloured, although it may be grey or brown, with vertical black bars on the
flanks. There are also two lines of alternating dorsal spots, although these are not always
distinct. However, there are several other subspecies of grass snake, with introduced
populations of Romanian origin present in Yorkshire (Nash 2011). This form has a prominent
pair of pale dorsal stripes along either side of the midline; snakes matching this description
have also been observed in the Newcastle area (Bond 2012, Coult 2012, Brian Banks pers.
comm.). Therefore grass snakes seen in Scotland may not be N. n. helvetica, as they could be
introduced forms.
Hatchlings and juveniles appear as miniature versions of adults. Although they may have
darker colouration, the pale neck collar remains conspicuous.
As with adders and other snakes, grass snakes that are preparing to slough off the old skin
to allow growth (ecdysis) can be recognised by cloudy, opaque eyes, along with a bluish tinge
and dull skin. The old skin breaks at the mouth, and is peeled off in a single piece through a
combination of rubbing against vegetation and muscular contractions. Ecdysis occurs at least
once during the active season. A study in Switzerland found that the first ecdysis occurred
in late June, with some individuals completing a second moult in August (Wisler et al 2008).
Grass snake sloughs do not usually show any clear markings, unlike adders where the zigzag
pattern is often still evident. Furthermore, adder sloughs exhibit keeled dorsal and flank
scales, whereas only the dorsal scales of a grass snake slough are strongly keeled.
In Scotland, the distribution of grass snakes has been confused by misidentification of two
other more common native reptile species, the adder and the slow-worm. However, there
are features that can be used to easily differentiate grass snakes from these species. These
Adult grass snake, showing the distinctive pale collar of the species, bordered by black triangular markings.
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The Amphibians and Reptiles of Scotland
are the pale neck collar and round eye pupil. Chequered garter snakes, which have escaped
from captivity (native to North and Central America), are also commonly misidentified as
grass snakes. However, these also lack the distinctive pale neck collar, although they may
have small pale markings on the flanks of the neck.
A grass snake will feign death if disturbed, rolling over onto its back with its forked tongue
hanging out. At the same time, a potent and foul smelling liquid is often released from the
anal gland. This may result in escape from predators which avoid feeding on carrion.
Grass snakes can live up to 15 years in the wild, and up to 20 years in captivity (Hand et al
2006, Wareham 2008). Males reach sexual maturity when they achieve a total length of 50
cm, at about three years. Females mature more slowly, reaching sexual maturity at 60 cm,
between four and five years in age (Madsen 1983, Hand et al 2006). Females grow faster
than males, although growth slows in both sexes at 8–9 years of age.
Eggs
Grass snakes lay eggs (oviparous) that are oval in shape, measuring roughly 2.8 cm long and
1.8 cm across (Spellerberg 2002). They have a thick parchment-like shell, are white or off-
white in colour, and are normally found glued together in clutches at egg-laying sites. The
pupa of the northern eggar moth may be confused for a grass snake egg, although close
examination will reveal the silk construction (Cathrine 2014a).
Current distribution
Until recently, it has generally been considered that grass snakes do not occur in the wild in
Scotland, although they are sparsely distributed in northern areas of England including
Cumbria and Northumberland (Arnold 1983, Inns 2009, Bond 2012, Beebee 2013). Grass
Grass snake eggs. These are about 2.8 cm long and 1.8 cm across.
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The Amphibians and Reptiles of Scotland
snakes were occasionally kept as pets in the 20th century and a number of records from the
Central Belt may represent escaped animals (Arnold 1995).
On 10 May 2010 a grass snake was recorded by Caledonian Conservation Ltd staff in
Dumfries and Galloway while undertaking great crested newt egg search surveys (Chris
Cathrine pers. obs.). The pond in which the grass snake was seen was far from any human
population centres, and located at the border of semi-natural mixed woodland and
agricultural land, suggesting it cannot be readily explained as an escaped pet, and is likely to
be wild or feral. It is interesting to note that grass snakes had previously been reported by
estate workers and fishermen in the same area, but these records had been dismissed
without further investigation, as this species was not believed to be present in Scotland.
This find encouraged research into other records. The current distribution in Scotland, as
described here, is based on this ongoing research. The latest information can be found at
www.caledonianconservation.co.uk.
After a verification process, described in Cathrine (2012) and Cathrine (2014b), four records
have been confirmed as grass snakes in a wild environment: three from Dumfries and Galloway
and one from the Scottish Borders. These records range in date between 1942 and 2010,
although three were recorded from 2009-2010. This is not necessarily an indication of recent
colonisation however, but more likely reflects the difficulties involved in verifying older records.
A further eight remain that cannot be immediately explained as erroneous or escapes, and
range in date from 1960 to 2004. Five of these possible records from Dumfries and Galloway
are from less experienced but reliable sources, but in appropriate habitat and relatively near
confirmed records.
Another record from Loch Lomond is from a reliable source, but may relate to an
introduced population as 200 grass snakes were released in the area at an unknown date
in the late 20th century.
Two independent records from Aberdeenshire seem unlikely, but in context become
interesting as both are in the River Dee catchment.
In addition, a small number of records of grass snake eggs and juveniles have been reported
recently in the Scottish Highlands. However, no records of adults have been received from
these areas. As climatic conditions further south in the Solway appear to be marginal in their
ability to potentially support grass snakes compared with the northern limit in Sweden, it
seems unlikely that the Highlands offer suitable conditions for egg development (Cathrine
2014a). Based on the available information it appears more likely that these records relate
to individual occurrences of eggs being transported with agricultural materials.
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History in Scotland
There has been much confusion over the distribution in Scotland due to the use of the common name ‘grass
snake’ to indicate adders in Argyll and slow-worms throughout much of the rest of the country, particularly
the Highlands (Cathrine 2012, 2014b).
Sowerby (1806 p. 5) reported a water snake in Dumfriesshire which he named Coluber dumfrisiensis, the
‘Dumfriesshire snake’. The validity of C. dumfrisiensis was challenged by Newman (1862), who proposes
that the species is in fact identical to C. lævis, the smooth snake (now Coronella austriaca of which
C. dumfrisiensis is often considered a synonym). The presence of the smooth snake in Scotland, which is a
species largely restricted to heathland habitats in southern England, seems remarkable. Furthermore, the
illustrations of C. dumfrisiensis do not appear similar to the smooth snake. Instead, they bear a greater
resemblance to the northern water snake, a native to North America. Therefore, the Dumfriesshire snake may
be an early example of an escaped exotic pet. While the origins of C. dumfrisiensis may never be known, it
does not seem likely to be a record of a grass snake in Scotland.
An unambiguous reference to the ‘water snake’, and so possibly a grass snake, in Scottish literature comes
in the form of ‘warlock-feckets’ in Cromek’s Remains of Nithsdale and Galloway Song: with Historical and
Traditional Notices Relative to the Manners and Customs of the Peasantry, published in 1810. Here, ‘warlock-
feckets’ are described as jackets woven of water snake skins, apparently popular among Satan’s crusaders.
Although this publication is now considered to be a hoax perpetrated by Allan Cunningham, a mason from
Dumfriesshire, who provided the materials to Cromek who was likely unaware of their fictitious origins, it is
interesting that they are linked to Nithsdale by a man from the area as this is within the apparent range of
the grass snake in Scotland.
A number of other 19th and early 20th century records in Scotland were deemed escapes by contemporary
naturalists (Taylor 1900, Leighton 1901, 1902, Sim 1903, Evans 1909).
Historical records suggest that grass snakes have been present in Scotland for some time. For example, the
confirmed record from the Scottish Borders refers to several sightings at the same location between 1942
and 1945, as does a possible record from the Rhinns of Galloway from the 1960s. There are many potential
explanations for the small number of grass snake sightings in Scotland. Grass snakes may be native to
Scotland but under-recorded, if the populations that exist are small or sparse, and are in areas where little
biological recording takes place. Alternatively they may have colonised Scotland relatively recently, as a
result of climate change or due to human activities such as deliberate releases, escaped pets or accidental
transport. Accidental introduction through the movement of agricultural materials (such as manure, compost
or hay) could occur as grass snakes use heaps of decaying organic matter as nesting and basking sites. This
species is now rarely kept as a pet and thus it seems unlikely that individuals found in remote parts of
Scotland would be escaped pets.
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The Amphibians and Reptiles of Scotland
Records of grass snakes in Scotland since 1942.
Data derived from NARRS, NBN and other
sources listed in the Introduction, and subjected
to a verification process: black dots - confirmed;
pink dots - possible.
Confirmed
Possible
1000
750
500
250
0
Altitude (m)
Scale (km)
50 1000
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The Amphibians and Reptiles of Scotland
At present, the ‘core range’ in Scotland appears to be Dumfries and Galloway and the Scottish
Borders (Cathrine 2014b). Given that grass snakes are known to occur in Cumbria and
Northumberland reaching the border between England and Scotland, this seems plausible. It
does not seem logical to conclude that the distribution of this species ends or begins at this
national border, as some published distribution maps suggest (Inns 2009, Beebee 2013).
It is possible that climate change will enable the grass snake to extend its range further north.
Research suggests this to be the case in Spain, where N.natrix was included in a study which
found a mean northward latitudinal shift of 0.5 km per year for thirty reptile species
(Moreno-Rueda et al 2011). However, a study of a wide range of taxa by Hickling et al (2006)
found that the northern latitudinal limit of grass snake distribution in the UK was stable,
although this finding was limited by the datasets available prior to the recent review
(Cathrine 2012), and data that have subsequently come to light (Cathrine 2014a, 2014b).
Therefore, while climate change may not have caused a recent colonisation event, it is
possible that it will enable future range expansion.
Habitat
Grass snakes are predominantly a lowland species, but occupy a range of habitats. In the UK
they are often found in open woodland, hedgerows, heathland and along road and rail
embankments. In agricultural environments, edge habitats are particularly important (Wisler
et al 2008). Elsewhere in Europe they have also been found to occur in coniferous forests,
including those on drained peat, although they appear to avoid active (peat forming) bogs
(Čeirāns 2004). The factors determining whether an area is suitable to support grass snakes
are related to availability of prey, particularly frogs and toads, suitable egg-laying sites and
the temperatures required for egg development.
Grass snakes have been found to be particularly associated with frogs and toads, which
constitute the primary prey items in most geographic locations (Gleed-Owen 1994, 1996,
Reading and Davies 1996, Luiselli et al 1997, 2005, Gregory and Isaac 2004). As such,
although grass snakes can occupy a variety of habitats they require access to freshwater
features where they can forage for amphibian prey.
The grass snake is the world’s most northerly, egg-laying reptile (Löwenborg et al 2012, Elmberg
et al 2013). Therefore, for a population to be sustainable, suitable egg-laying sites must be
present. Grass snakes occur at higher latitudes in Scandinavia, where the most northerly known
population is found at 62°15’N in Sweden, which is further north than the Aberdeenshire records
(Elmberg 1995, Johan Elmberg pers. comm.). Elsewhere, the northern extent of the range has
been found to be at least 64°24’N, which is more northerly than the limit of mainland Scotland
(Löwenborg et al 2010). Grass snakes become increasingly dependent upon humans
(synanthropic) further north in their range, relying on man-made compost heaps and manure
piles for egg-laying sites (Löwenborg et al2010, Hagman et al2012). However, in 2014 a grass
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The Amphibians and Reptiles of Scotland
snake was recorded to use a natural egg-laying site as far north as 59°45’N, at Filipstad, near
the northern Swedish border in the province of Värmland (Johan Elmberg pers. comm.).
However, given the climatic conditions in Scotland, it is likely that grass snakes are restricted
to using man-made egg-laying sites, such as compost heaps and manure piles.
A common reason historically cited for grass snakes not occurring in Scotland is that the climate
is too cold to support the development of eggs, and that this is why the three widespread native
reptiles in the country are all viviparous (Buckley and Cole 2004). However, it should be noted
that there is an established introduced population of sand lizards on Coll, an egg-laying species
(Buckley and Cole 2004, Bowler and Hunter 2007, Inns 2009, Beebee 2013). Interestingly,
however, preliminary climate analysis comparing a decade of data from the weather stations
nearest to the confirmed grass snake records in Scotland (Eskdalemuir observatory) and the
most northerly confirmed contemporary record from Sweden (Delsbo observatory) highlights
an important difference: mean monthly maximum temperatures in June, July and August at
the northern fringe of grass snake distribution in Sweden are higher than those in Dumfries
and Galloway during August (Cathrine 2014a). This is significant, as these are the key months
for egg development, which is highly temperature dependent. However, data used from
Eskdalemuir are from a higher elevation than the apparent core range of grass snakes in
Scotland, and so analysis of weather data from the Solway may clarify this picture.
Although it has not been confirmed if grass snakes are presently breeding in Scotland, they
may have done so in the past. It is interesting to note that all confirmed records and most
Habitat suitable for grass snakes in Scotland. The species is usually present near water where it finds prey
items such as common frogs and common toads. The warmth of manure piles attracts adults and can be
used to incubate eggs; such manure piles are especially important in northern parts of this species' range.
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The Amphibians and Reptiles of Scotland
Grass snake hunting in water. Many of the prey items are common frogs and common toads.
possible records are in or near areas offering semi-natural woodland, freshwater habitats and
agricultural land that provide manure piles and compost heaps for egg-laying (Cathrine
2014b). Therefore, suitable egg-laying sites are available, and it is possible that grass snakes
currently breed in Scotland.
Grass snakes can have large home ranges. Madsen (1984) found that males held an average
home range of 17.3 hectares and females 24.9 hectares. Males are highly mobile, moving
around 50 m in a day during the mating season, and about 10 m per day later in the year.
Females, however, are more sedentary but can move more than 100 m in the week prior to
and after egg-laying. In an agricultural landscape, female grass snakes were found to have
home ranges of 15.1–120.5 hectares, with a mean of 39.7 hectares (Wisler et al 2008).
Elsewhere grass snakes are reported to hold home ranges between 3 and 120 hectares, and
may move 10–300 m in a day (Arnold and Ovenden 2002).
Annual cycle
The grass snake has not been subject to extensive study in Scotland, so it is not currently
possible to determine a geographically specific annual cycle. However, the species in Scotland
may be expected to follow a similar annual life cycle to populations in England, and possibly
other European countries.
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The Amphibians and Reptiles of Scotland
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Hibernation
Active
Ecdysis
Mating
Gravid/egg-laying
Egg-hatching
Grass snakes hibernate between October and March, using hibernacula within hedgerows,
banks, tree roots, mammal burrows, buildings, straw heaps, road embankments and even
burial grounds (Frazer 1983, Ritter and Nollert 1993, Mertens 1995, Luiselli et al 1997, Hand
et al 2006, Löwenborg et al 2010). They emerge in spring, with males usually appearing first,
between March and April, and mating taking place from April to May. Females secrete a
pheromone trail, which males follow, sometimes with multiple snakes in a line. All of the
males will attempt to mate with the female, which may sometimes result in a ball of snakes,
although only one will be successful.
Grass snakes have been found to maintain an active body temperature of 30°C (Mertens
1994). In the northern part of their range, thermoregulatory opportunities are limited (Isaac
and Gregory 2004). Snakes bask to maintain body temperature, with gravid females basking
more frequently than males or non-gravid females (Madsen 1987). This has the effect of
reducing feeding opportunities for gravid females (Gregory et al 1999).
Eggs are typically laid between June and July (Frazer 1983, Spellerberg 2002). Clutch sizes
are variable, with reported ranges from 4–40 (Madsen 1983, Luiselli et al 1997, Spellerberg
2002) to 2–105 eggs, with an average of 30 (Arnold and Ovenden 2002). Fecundity has also
been shown to increase with the size of the snake (Madsen 1983). Grass snakes can lay eggs
communally, with up to 3,000 to 4,000 being recorded at the same site (Arnold and Ovenden
2002). Incubation lasts 22–45 days, and is shorter at constant, higher temperatures (Luiselli
et al 1997, Löwenborg et al 2012). Natural egg-laying sites include rotting wood, wet moss,
under rocks, in loose soil and disused mammal burrows. In Sweden these have been found
to provide average incubation temperatures of 15.5°C, mirroring the ambient air
temperature, and thus making them generally unsuitable for egg-laying (Street 1979, Luiselli
et al 1997, Löwenborg et al 2010, Baker 2011). Given that the climatic conditions in Scotland
are marginal compared with those at the northern range in Sweden, it is likely that grass
snakes here are restricted to using man-made egg-laying sites (Cathrine 2014a). Studies have
shown that grass snakes prefer to lay eggs in compost heaps providing an average
temperature of 20.6°C, although this varies widely during incubation; and manure heaps
providing an average temperature of 30.7°C, varying by less than 2°C (Zuiderwijk et al 1993,
Löwenborg et al 2010, 2012). Less than 5% of eggs hatch when incubated at a temperature
Annual life cycle of the grass snake (based on data from England and Sweden).
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The Amphibians and Reptiles of Scotland
of 19°C, whereas 70% hatch successfully between 21°C and 31°C. Incubation takes twice as
long at 19°C compared with 31°C. Similarly, hatchling fitness is reduced at lower temperatures.
It is therefore not surprising that even when natural egg-laying sites are available to grass
snakes, they prefer man-made manure and compost heaps that provide higher temperatures.
The boost in incubation rate which results from this behaviour provides an advantage in areas
where the active season is shorter (Löwenborg et al 2012). This has allowed the grass snake to
extend its range further north than any other oviparous snake. However, some developmental
problems, such as smaller size, slower speed, and longer hatching times, are higher where
temperatures fluctuate as occurs in compost heaps (Löwenborg et al 2011). Despite this, grass
snakes appear to use compost heaps and manure piles equally.
After mating snakes move to areas to feed (Phelps 1978). These are typically wet habitats,
where amphibians are present. Grass snakes have been found to eat large meals every
20 days, on average, between May and September, with a mean daily food consumption of
1.6–2.3% of their body weight (Reading and Davies 1996). However, gravid females fast for
around 45 days during gestation and egg-laying. During this period, female grass snakes bask
more frequently than males and non-gravid females (Madsen 1987). Consequently gravid
females can lose weight as a result of the conflict between feeding and thermoregulatory
behaviour (Gregory et al 1999, Gregory and Isaac 2004).
Hatchlings are about 20 cm long when they emerge in August, and generally do not eat until
the first slough, which usually occurs at around two weeks (Luiselli et al 1997, Löwenborg
2010). The sex ratio at hatching is normally 1:1, and this is maintained with age (Mertens 1995).
Grass snakes usually produce only a single clutch per year, and do not appear to reproduce
every year (Luiselli et al 1997). Due to the contracted season at the northern limit of its
range, opportunities to produce second clutches in Scotland will be even more limited than
elsewhere in Europe. Mating activity has been observed in autumn in northern England,
though this has not been shown to result in egg production (Coult 1989, 2012).
After feeding through the summer period, snakes return to hibernation areas in later summer
and autumn to hibernate from October.
Juvenile grass snake. These are about 20 cm long on hatching.
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The Amphibians and Reptiles of Scotland
Diet
Grass snakes primarily feed on amphibians, and particularly frogs and toads, which make up a large proportion
of the diet in most populations, although newts are also eaten (Gleed-Owen 1994, 1996, Reading and Davies
1996, Luiselli et al 1997, 2005, Gregory and Isaac 2004). However, they can also eat a range of other taxa,
including common lizards, small mammals, fish and birds (Arnold and Ovenden 2002, Spellerberg 2002).
A study in Italy that compared the diets of grass snake populations in different habitats found that while frogs
and toads constituted the main prey items in the majority of populations, newts and salamanders were the
primary prey item in populations in montane and colder environments (Luiselli et al 2005). Similarly, small
mammals have been found to be the main prey item for populations living in intensive agricultural
environments with no patches of semi-natural habitat. Grass snakes have also been observed, rarely, to feed
on carrion. Given the abundance of frogs and toads in most Scottish habitats, it seems likely that these would
constitute the main prey items in most if not all areas.
The size of prey items has been found to be positively correlated with the size of the individual grass snake:
large grass snakes do not tend to eat small frogs and toads, even though they are capable of doing so (Reading
and Davies 1996). Small grass snakes tend to eat recently metamorphosed toadlets, whereas males shift towards
adult toads as they become larger (Luiselli et al 1997). Large females are capable of taking much larger prey,
such as adult toads and mice. Prey items are typically swallowed head first (Gregory and Isaac 2004).
Population estimates
At present, there is insufficient information to make a population estimate for the grass snake in Scotland.
The species may be Scotland's rarest native reptile, and appears to be present at only low densities in the
south of the country (Cathrine 2014b).
Threats
Due to the limited amount of information available about grass snakes in Scotland, specific threats are unclear.
However, development of sites along the Solway coast and changes to agricultural practices could threaten
the species through destruction of habitat in the south of the country, where the climate is most likely to
support populations. Furthermore, land management changes made in order to improve grazing on the
Solway for agricultural gain could have a negative effect on grass snake populations through changes to
hydrology and amphibian prey populations.
As grass snakes often rely on man-made egg-laying habitats at the northern limits of their distribution, any
changes in agricultural practices that reduce availability of these may also result in a population decline or
range contraction. A reduction in land holdings with livestock has been shown to correlate with a decline in
grass snakes in Sweden, and it has been inferred that this is a result of the loss of manure heaps, used as
egg-laying sites (Hagman et al 2012).
Given their association with agriculture, grass snakes are also at risk of coming into contact with and being
harmed by pesticides (Fryday and Thompson 2009). This risk may be increased where poor agricultural
When and where to see grass snakes
Grass snakes may be Scotland’s rarest native reptile. Their distribution is poorly understood, but appears to
be focused on Dumfries and Galloway. However, where grass snakes have been found they occur at low
densities making detection difficult. Snakes are active from March through to September. Chances of detection
can be improved by using artificial cover objects made of roofing felt or corrugated iron, or by checking
compost heaps and manure piles, where adults and eggs may be found.
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The Amphibians and Reptiles of Scotland
Legal protection
Partially protected by law. If found to be native, it is illegal to injure, kill or sell grass snakes. See Appendix B
for details.
The grass snake will feign death if disturbed, rolling over onto its back, with its tongue hanging out.
practices result in runoff into watercourses and water bodies that may be used by grass snakes and their
amphibian prey.
As with other snakes and reptiles, grass snakes have been found to be vulnerable to being crushed by motor
traffic, while basking on road surfaces. Juveniles are particularly susceptible to this, with higher mortality on
cool days when mobility is limited by the lower temperatures (Ciesiołkiewicz et al 2006). Indeed, walking
roads in suitable habitat in suburban and rural Sweden during September can be an effective way of locating
juvenile grass snakes (Chris Cathrine pers. obs.).
At the time of writing, the status of grass snakes in Scotland is unclear, and knowledge of their presence is
still being disseminated amongst the ecological community. This uncertainty and a low level of awareness
of the presence of this species amongst ecologists may lead to grass snakes not being considered adequately,
if at all, when undertaking Ecological Impact Assessments for developments, or when other decisions which
result in a change to land management are made.
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The Amphibians and Reptiles of Scotland
Gaps in current knowledge
Existing potential records warrant further investigation, while surveys in Dumfries and
Galloway will help determine the extent of the population and confirm whether grass snakes
currently breed in the wild in Scotland. Habitat suitability modelling could identify the areas
of Scotland capable of supporting populations, allowing further targeted surveys.
Post-glacial colonisation of the UK and Europe by some animals involved multiple events
following different routes, or successional waves with different subspecies persisting in the
north after they had been replaced in the south, either through displacement or interbreeding
with new arrivals (Hewitt 1999, Piertney et al 2005, Heckel et al 2007, Searle et al 2009,
Senn et al 2014). Variation in climate and habitat during this time has allowed animals to
establish populations throughout the country which have subsequently become isolated as
conditions changed; for example, great crested newts in the Inverness area have recently
been found to represent a native isolated population (Hewitt 1999, Jehle et al 2013). A similar
scenario should be considered when investigating grass snake distribution in Scotland, as the
species may have colonised the country during a period with more favourable climatic
conditions. However, it is possible that topography and habitat may prevent grass snakes in
Dumfries and Galloway from moving north (Cathrine 2014b).
Further research is required to clarify the range and origins of Scottish grass snakes. In
particular, photographs and genetic studies may help determine which subspecies is present.
Further comparison between climate data from the northern limits of the species’ range in
Scandinavia and verified records in Scotland will also assist with understanding the potential
limitations to grass snake distribution in Scotland (Cathrine 2014a).
In most populations, frogs and particularly common toads make up the majority of grass snake
diets. However, in Italy it has been found that newts and salamanders become the dominant
prey items in montane and colder environments (Luiselli et al 2005). Therefore, research on
grass snake diet in Scotland may reveal whether there are similar differences in the UK.
Encouraging further recording amongst experienced biological recorders and the wider public
will also help provide a clearer picture of the distribution of this species in Scotland.
Guest author: Chris Cathrine
Chris McInerny is a Reader at the University of Glasgow. He has a long-term
interest in natural history, particularly birds, mammals, butterflies, amphibians,
reptiles and orchids. He was President of the Scottish Ornithologists' Club
(SOC), is Secretary to both the Scottish Birds Records Committee (SBRC) and
the British Ornithologists' Union Records Committee (BOURC), and will be
Chairman of Biological Recording in Scotland (BRISC). He was an editor and
author of The Birds of Scotland published by the SOC in 2007, and has
published about 50 scientific papers on various aspects of natural history. He
has studied reptiles long-term at sites on the shores of Loch Lomond.
Pete Minting is Scottish Project Officer at the Amphibian and Reptile Conser-
vation (ARC) Trust. He completed his PhD on the effects of the chytrid fungus
Batrachochytrium dendrobatidis on natterjack toad populations in the UK in
2012. He has also worked as a biologist for Ayrshire Rivers Trust from
2004–2008, the Kalahari Meerkat Project in 2003–2004 and the Barbados
Sea Turtle Project in 2002. He completed a degree in Behavioural Science at
the University of Nottingham in 1995, and an MSc in Aquatic Resource
Management at King's College, London in 1997.
Chris Cathrine is Director of Caledonian Conservation Ltd, an ecological
consultancy based in Scotland. His passion for the natural world was sparked
when he was four, looking at reptiles, amphibians and invertebrates with his
grandfather. He has been the Scottish representative for Amphibian and
Reptile Groups of the UK, is a member of Central Scotland Amphibian and
Reptile Group and the Chartered Institute of Ecology and Environmental
Management (CIEEM). He has conducted research into grass snakes in
Scotland, undertakes surveys and has developed mitigation for a range of
projects. Chris is keen to share the wonder of Scotland’s amphibians and
reptiles, and to conserve them for future generations.
David O’Brien has been fascinated by reptiles and amphibians since catching
his first snake when aged four. He has worked on several long-term projects
in Scotland including the origin, genetics and conservation of great crested
newts in the Highlands; the role of Sustainable Drainage System ponds as
habitats, wildlife corridors and places where town-dwellers can experience
nature; and the biogeography of amphibians on islands. David is also involved
in projects looking at the interaction of reptiles and predatory birds; the role
of citizen science in mapping European wildlife; and predation response
amongst amphibians.
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