Grass Snake

Nomenclature

Common name:  Grass snake   /SARG/13000-Identification/snakenegative.jpg
Taxonomy:  Natrix natrix helvetica (Linnaeus 1758)
Other Names:   Collared snake
Neidr y gwair (Welsh)
Ringed snake (Archaic)
Common snake (Archaic)
Green snake (Archaic)
Hedge snake (Archaic)
Water snake (Archaic)


Introduction

/SARG/08000-TheAnimals/SpeciesPages/Grass_Snake/Grass_Snake_Portrait.jpg
The Grass snake.

The Grass snake is Britain's largest native terrestrial reptile, and probably its most common species of snake. Grass snakes, along with Slow worms, are the reptile that is most likely to be encountered in a garden, if you are lucky.

The Grass snake grows to over a metre (3-feet) long, and is strongly associated with water habitats, including garden ponds.

It is completely harmless to man, and almost never bites, even when caught. As with all native reptiles, it is illegal to harm or kill them.

Grass snakes are particularly associated with water.
Grass snakes are particularly associated with water.

Identification

/SARG/08000-TheAnimals/SpeciesPages/Grass_Snake/Grass_Snake_Head.jpg
The black and yellow collar forms a band or ring immediately behind the snakes head.

The Grass Snake is most easily identifiable by the interlinked black and yellow collar which usually forms a band or ring immediately behind the snakes head. However, such a collar is missing from sub species n. astreptophorous, which normally inhabits the Iberian peninsula but can also be found in Jersey.

The upper body is normally olive green or olive brown with black vertical bars along the flanks and which are interspersed by parallel rows of black dashes or dots, varying in size and shape and depending upon each individual snake, but, on the underside, the ventral scales of buff, cream or white have an equally individual chequered pattern in black.

The face has marked slashes and bars of black on each side below the eye and which form a method of individual identification.

© Tony Phelps
© Tony Phelps
 © D Sweeting
© D Sweeting
 Coiled Grass snake
Coiled Grass snake

Morphology

Occasional cases of polymorphism turn up and have been recorded in the UK, including several sightings of melanistic individuals, off white/buff and completely green colouration although these sightings are very rare.

Melanistic Grass snakes are uncommon. © John Newton
Melanistic Grass snakes are uncommon. © John Newton
 Markings like this are very rare. © Tony Phelps
Markings like this are very rare. © Tony Phelps
 Striped morph © Robert Vaughan
Striped morph © Robert Vaughan

Sexual Dimorphism

The female of the species may grow up to 1.2 metres in length (Snout To Vent), however, more mature individuals have been reported as being in the region of 2 metres in length. The male is more frequently tiny in comparison and individuals of around 600mm are usually among the largest specimens recorded.

the female is much larger than the male generally and the head of the female is much more pronounced in being triangular in appearance with eyes deep set into the cheeks whereas the male has an altogether more slender head with eyes that often protrude beyond the line of the face and jaw. The majority of females tend also to possess two post ocular scales as opposed to the males three post ocular scales and the female will normally have a much shorter tail to body ratio with a marked difference between body and tail width. It is usual for the female to possess between 52-56 sub caudal scales, while the tail of the male (which tends to taper more gently from the vent, but, often with a bulge at the base of the tail) will have between 68-72 sub caudal scales, therefore making up to a third of total length.

Comparative pictures of female and male heads. © Robert Vaughan
Comparative pictures of female and male heads. © Robert Vaughan

Could be mistaken for...

There are three other species of snake found in the UK, but only the Grass snake has the black and yellow collar behind the head. The Adder has a distinctive zig-zag pattern along its back, and the rare Smooth snake (only found in a few Southern counties) is plainer in pattern. Both of these two species lack the Grass snake's collar.

The Aesculapian snake is an introduced species to the United Kingdom, and is only known to breed at Colwyn in North Wales, and on the Regent's Canal, by London Zoo. Juvenile Aesculapian snakes do have a light collar, and have been confused with Grass snakes. Aesculapians do not have the dark collar that is almost always adjacent to the yellow collar of the Grass snake.

Grass snake (left) with Smooth snake (right) © Owen Burnham
Grass snake (left) with Smooth snake (right) © Owen Burnham
Adder
Adder
Sub-adult Aesculapian snake © John Newton
Sub-adult Aesculapian snake © John Newton

Distribution

Natrix natrix helvetica is most commonly thought of as the British Grass Snake, although its range extends east to Belgium, Germany, Sweden (where it overlaps with Natrix natrix natrix) and the Netherlands. Further east and south, its range is supplemented by other sub species namely, astreptophora, Cetti, Corsa, Cypriaca, Fusca, Gotlandica, Lanzai, Persa, Schweizeri, Sculata, Sicula, Syriaca and Tessellata, 15 (fifteen) sub species in total, although there is some disagreement as to the exact status and classification of these. And only Schweizeri in Greece and Cetti in Sicily currently occupy a position on the “Red List” of European endangered species.

The distribution of the Grass Snake stretches across the paleartic region from Russia to the UK and from Spain and Greece in the south, up to Sweden and to the latitude of 65 deg North. They have been recorded from the Balkan peninsula to the Iberian peninsula, although, many areas will not support a local population because of local ground conditions and/or climate, such as the colder, shorter summers experienced upon higher ground.

Their distribution across England and Wales is becoming patchy, although with increased public awareness and changing attitudes, the provision of man-made egg laying sites, hibernacula installations and refuges in gardens such as landscaping and water features like ponds, may yet make an important difference to numbers and the frequency of local populations.

Because the Grass Snake enjoys a specialised diet that includes prey items which take on both land and water borne phases annually, Natrix natrix can be found in a wide variety of macro habitats and soil type is not the primary concern, however, where ground cover is naturally restricted in mountain regions, or open and barren moors, then the incidence of natrix will be considerably reduced. They are not commonly found in Scotland, Ireland or large areas of Wales and even the counties of Wiltshire, Cornwall and Devon have areas within them where the ground conditions are not conducive to the Grass Snake life cycle.

National distribution

National distribution for the Grass Snake

Surrey distribution for the Grass Snake


Habitat

Ponds, lakes and rivers are the preferred habitat of the Grass Snake, but, not only are features such as bank-side vegetation important to provide cover against predatory hawks and herons for instance, there must be readily identifiable passages of ground cover in the form of ditches, hedges or banks of brambles which lead up to the pond’s banks. If such passages are removed from the surrounding environment, then the frequency at which Grass Snakes will visit a particular pond will reduce.

Just because a pond may hold a suitable prey items, does not mean that the Grass Snake will populate the water body, because a lack of local cover or the frequency of higher predators may prevent such.

When their prey take on their land borne phases, which occurs from mid summer, (June or July depending on weather) then the Grass Snake will move to drier surroundings and can be found in forest clearings, woodland edges and gardens.

With the increased growth of cities, suburban developments and human activities, the inevitable disturbance to the wilder and quieter quarters of the countryside has impacted upon the migration routes of the Grass Snake and so numbers have diminished substantially over the last ten to fifteen years. The decline in Grass Snake numbers is such, that, there is now genuine concern for their status within the UK in general and as the Grass Snake does not frequent Scotland (although it has been sighted there on occasion), mainly because of the colder climate, suitable habitats around bodies of water where amphibians are still plentiful are themselves becoming scarce.

Coupled with this, as the Grass Snake is mainly diurnal in its habits, it is further restricted in its activity than say that of the Adder, in that it cannot use the cover of darkness to hunt and is therefore more prone to predation especially where ground cover is removed to provide recreational facilities and parks. This may be compounded by the fact that the snake is harmless in that it does not possess venom glands or fangs.

Grass Snakes will frequent many different soil types as long as ground conditions are not too acid or alkali which may then deter prey items such as frogs, toads and newts from inhabiting an area (as their skin is permeable and susceptible to irritation) and as long as day time refuges such as crevices, hollowed, fallen logs and/or suitably dense vegetation allows good cover and shade.

Well vegetated riperian habitat is ideal for Grass snakes - although they may equally be found on heathland in late summer.
Well vegetated riperian habitat is ideal for Grass snakes - although they may equally be found on heathland in late summer.

Activity

Grass snakes will often slough their skins in groups and at the same time of year. As the shedding process is linked to growth, weather patterns and stage of life, this is dictated locally by conditions found at any given location, so that when one skin cast is found, there is frequently up to seven or eight others to be found in the same vicinity. As the sloughing process is usually undertaken between every 6-10 weeks and given that the cycle from dulling of colour and fogging of the eye lens caps, through to the actual shedding is between 7 and 10 days, some overlap would be inevitable, but not to the extent where the whole group is coordinated, so how and why the Grass snakes employ this group strategy is still unknown.

January


  • Hibernation

February


  • Hibernation

March


  • Early emergence

April


  • Courtship

May


  • Diurnal activity

June


  • Egg laying

July


  • Diurnal activity
  • diet switches to terrestrial amphibians

August


  • Diurnal activity

September


  • Juveniles hatch

October


  • Return to hibernacula sites

November


  • Hibernation

December


  • Hibernation

Food

/SARG/08000-TheAnimals/SpeciesPages/Grass_Snake/Grass_Snake_Frog.jpg
A Grass snake eating a Common frog.

The Grass Snake’s diet has preferences which relates directly to the time of year. From March, when the snakes emerge until mid may, they will take greater quantities of small fish, mainly because the fish are spawning during this period and are easier for the snakes to catch among the weedy fringes of water bodies. Grass snakes can often be seen lying still among lilly pads and stalking the flapping fish.

From May until late June/early July, the emphasis falls onto Newts (including Great Crested variety), and again, that is because the newt’s own life cycle doesn’t include a land-borne phase until after July. From July, the snakes gradually disperse away from ponds and into forest clearings, wooded copses and longer grasses / ground cover and a higher number of Frogs and Toads will then be taken as a result. The frogs and Toads themselves had generally moved away from the ponds by April, although some are obviously predated upon between the cross over of snakes arriving at ponds in Spring and while the frogs/toads are migrating away from them.

Nests of very young chicks such as moorhens are sometimes consumed by Grass snakes, (mainly to supplement an otherwise restricted diet), as are mice/voles, especially by the more mature female snakes, but these incidents are rare. The neonates of Grass Snakes will take young/small fish, late tadpoles, and the newly metamorphosed new generation of frogs and toads and there is also some mention that worms have been consumed occasionally by Grass Snakes but this has not been scientifically proven.

Small fish.
Small fish.
Newts in aquatic phase.
Newts in aquatic phase.
Common frogs in terrestrial phase.
Common frogs in terrestrial phase.

Predators

/SARG/08000-TheAnimals/SpeciesPages/Grass_Snake/Grass_Snake_Possum.jpg
The Grass snake will 'play dead' to dissuade predators which prefer live prey.

The Grass snake suffers predation by many species, including; domestic dogs, birds of prey, man, herons, pheasants, corvids, mustalids, hedgehogs, foxes and even terrapins. Neonate Grass snakes are particularly susceptible to predation by cats, pheasants and blackbirds.

The main defence that the Grass Snake possesses against predation is the expulsion of a secretion from the anal glands and is mixed with faecal matter from the cloaca and which is pungent enough to discourage some attacks. Failing that, the Grass Snake has been known to play dead, by inverting itself, so that the ventral scales are shown to an aggressor and which is accompanied by the snakes jaw being held agape with the tongue protruding as though lifeless.

Like many other colubrids, the Grass Snake does not possess venom glands or fangs and is harmless to human beings although they have been known to bite on very rare occasions.

Young pheasant predating a juvenile grass snake © <i>John Tomsett</i>
Young pheasant predating a juvenile grass snake © John Tomsett
Mustalids (polecat)
Mustalids (polecat)
Domestic cat (Wooster)
Domestic cat (Wooster)

Shelter

Grass snake hibernacula are typically either rabbit burrows, or root systems of trees, provided that raised ground allows well–drained soil. Occasionally they are found under farm buildings, in hay stores and even in compost heaps in sheltered spots and where the temperature is generally higher than that of the surrounding environment.

Favourite haunts during active period includes among mosses attached to roots of Heather, in deep piles of leaves, under over-hangs of banks of well fringed ponds, in the rotten stumps of fallen trees and hollowed logs.


Reproduction

/SARG/08000-TheAnimals/SpeciesPages/Grass_Snake/Grass_Snake_Eggs.jpg
Grass snake eggs, found in pig dung.

The Grass Snake can be found in spring (upon emergence from hibernation), to participate in “mating balls”, where up to 8 (eight) males and one-two females congregate in a tight and writhing mass that can resemble a ball of rope and can be a hub-bub of activity for up to two hours. Although there seems to be no one “alpha” male that predominates in the mating process, the male suitor is merely that that manages to couple before any of the others. It has been noted that even some of the smallest males in any group can be the active mate in coition, simply because that particular male’s hemi-penes have become ensnared within the female cloaca and thus excluding others, although, the female may mate with many males during the spring period generally.

The mating ball congregations usually form with the female basking in temperatures above 13 deg c, with an open cloaca and which then attracts males to her vicinity. Once located the male will attempt to uncoil the female with a constant intertwining of his body through hers and until their vents can be aligned and positioned for the mating process. No other form of dance or ritual like that of adders has been noted, although female Grass Snakes have been known to retreat rapidly from such mating balls and for no particular reason, but are then actively pursued by the group of males so it sometimes seems as though they are charging together through the ground cover.

Once gravid, the female may not reach ovulation and oviposition of eggs for two months or so, (again, depending on weather conditions) and the size of egg clutch will be determined by and have a direct correlation with, the size of the female herself. Young females may carry only 7-15 eggs, while more mature females can increase to a clutch of mid twenties while some of the largest females (rarely) can produce up to forty eggs, but then the snake would need to be at least ten years old, in order to produce a clutch of that size.

It is thought that clutches of eggs may have anything between 45% - 75% success rate of hatching into neonates and that around 50% of these survive to a breeding age.


Juveniles

The juvenile Grass Snake is generally a miniature version of the adult with the collar markings etc present from birth. The incubation period is around 70 days from oviposition to hatching, though the weather will have a major impact on the period and lower temperatures and longer incubations bringing more female offspring as a result and higher temperatures / shorter incubation bringing a higher percentage of males.

All neonates leave the egg with an umbilical chord attached but which withers and breaks away, sometimes within hours but sometimes taking up to two days to detach fully.

The neonates will normally always consume prey before hibernation although it is thought that the first hibernation period sees the greatest losses in Grass Snake numbers, partially due to lack of suitable prey and inexperience in locating deep enough hibernacula where frost can be avoided.

The young of the Grass snake upon hatching are usually between 148-150mm in length and in the first year, this will have increased to 210-220mm. The young males are thought to become sexually mature before they reach 300mm in length.

A juvenile Grass snake is a minature of an adult.
A juvenile Grass snake is a minature of an adult.
 Juvenile Grass snake - held to demonstrate size.
Juvenile Grass snake - held to demonstrate size.
Ventral surface.
Ventral surface.

Conservation

The estimated Grass Snake population in the UK is suggested to be around 365,000 snakes, however, losses in the last fifteen years means that this figure is expected to be a considerable over-estimate and may now be as low as 180,000.

Natrix natrix helvetica has only minimal protection under the Wildlife and Countryside Act, which bans the taking for sale, killing or injuring of any Grass Snake, but which does not protect their habitat per se.

Although both the UK’s and the European biodiversity plans hint at conservation, the specialised niche of the Grass Snake and its needs are not addressed in any SSSI’s or SAC’s within the UK, although two sub species are protected fully under European law, namely Natrix cetti and Schweizeri.

Areas such as Minsmere in Suffolk, Purbeck in Dorset and also within the New forest, provide hope that long term conservation of the species can be achieved although in more urban situations and suburban areas without green belt, the population losses are unlikely to stabilise without even greater introductions of garden ponds and sympathetic gardening practices that allow for ‘wild areas’ to remain.


Designation Applicability
Species of conservation concern:   Yes (Long list)
CITES (1975):   No
Bonn Convention (1979):   No
Wildlife & Countryside act (1981):   Yes (Sch. 5) 9.1, 9.5a, 9.5b
Bern Convention (1982):   No
Conservation Regulations (1994/2007):   No
EC Habitats & Species Directive:   No
IUCN Red List:   Not Listed


Information

Principal Author: Main Illustrator: Review: Updated:
Robert Vaughan Various Reviewer 03 Jul 2008