The Grass Snake Natrix natrix is the largest British terrestrial reptile. Male Grass Snakes average about 65 cm in length and females 75-80 cm, the largest recorded British Grass Snake being 1.8 metres in length (Beebee and Griffiths, 2000) and the largest recorded Grass Snake in our region being 98 cm (Coult, 2012). Typical Grass Snake colouration is an olive green to brown background with a row of vertical black bars along each flank and two lines of dorsal black spots. The underside is black and white checked. The most conspicuous feature is the yellow/orange and black collar behind the head, which is the source of its older name, the Ringed Snake. Some County Durham Grass Snakes exhibit atypical colouration with the collar either absent or much reduced and a pair of pale dorso-lateral stripes, a colour form associated with Eastern European Grass Snakes (Coult, 2012).
During the winter Grass Snakes hibernate underground or under cover in frost-free locations, emerging in March or April to bask in the sun, raising the body temperature prior to mating. In June pregnant females lay eggs in piles of damp rotting vegetation, where heat generated by decay helps them to hatch. Good egg-laying sites may be used by several females. In Durham and Northumberland only two egg-laying sites have been recorded and both were manure heaps (Coult, 2012). Grass Snakes have been recorded breeding in Northumberland twice, around 1984 at Wallish Walls (Ken Hopper, pers. comm., 1984) and at Fontburn Reservoir in 1999 (John Durkin, pers. comm., 2000). In Durham breeding has been recorded several times on the Gibside Estate in the Derwent Valley (Coult, 2012). Occasionally autumn mating is reported including a September mating in County Durham (Coult, 1989 and 2012). Eggs hatch in August or September but it is unlikely that eggs laid as a result of an autumn mating could survive the winter in the wild. With the onset of cold weather the snakes will return to hibernation.
Grass Snakes require home ranges which include hibernation, feeding and egg-laying sites along with secure places to bask in the sun. On occasion they will climb into low shrubs to catch the last rays of sunlight and two of the earliest records of Grass Snakes in Northumberland describe climbing snakes in the Cheviots near Ingram and in Middleton Plantation near Wooler (Leighton, 1901).
As amphibian and fish eaters Grass Snakes are closely associated with wetland habitats, ponds, marshes and river valleys. Having no specialist adaptations for killing prey they prefer species such as frogs, toads and newts which cannot bite back and can be seized and swallowed alive with no risk to the snake. The swallowing of a large frog can take some minutes and I have seen a Grass Snake regurgitate a frog alive on being disturbed only to catch it again and complete the swallowing process. Grass Snakes themselves are occasionally taken by predators and Henry Tegner the Northumberland naturalist records one as prey in a Kestrel’s Falco tinnunculus nest at Langleeford near Wooler (Tegner, 1972).
Grass Snakes are very rarely encountered casually. Intentional surveys have become increasingly unproductive as the Derwent Valley population has declined. Survey methods are similar to those described for Common Lizards Zootoca vivipara, but with areas close to amphibian ponds and suitable egg-laying sites being targeted.
Grass Snakes are generally distributed throughout lowland England and Wales in suitable habitats becoming rarer in the north of England, and are usually described as absent from Scotland with any Scottish records assumed to be introductions. They are not found in Ireland (Beebee and Griffiths, 2000). A recent review of Scottish records however indicates that some records from the south west of Scotland may be indigenous snakes (Cathrine, 2012).
In the North East Grass Snake records occur as far north as Crookham within four miles of the Scottish border (Leighton, 1901) and are well dispersed in time and space across Durham and Northumberland. There are scattered records throughout County Durham, with a concentration along the valley of the River Derwent. There are no records from the valley of the River Tees and the Tees plain. There are 21st century records around Ingleby Greenhow on the northern edge of the Cleveland Hills. The earliest Northumberland records are those in Leighton (1901), which are extracted from the “J.A.” articles in the Newcastle Weekly Chronicle of 1881, and in Durham, Fawcett (1900) recorded the Grass Snake in the Browney Valley in 1883.
The 19th century records were not universally accepted as true, particularly by the natural history establishment; Richard Howse, then the curator of the Hancock Museum, wrote “My opinion is that the Ring Snake does not occur here except accidentally” (Leighton, 1901) and George Bolam wrote “Of the Grass or Ringed Snake (Tropodinotus natrix) there are I believe no Northumbrian records, and very few (if any) well authenticated ones for Durham” (Bolam, 1917). Although it is now proven that Grass Snakes are or were resident in Northumberland and Durham, doubt over the validity of Grass Snake records persists to this day, with errors in identification caused by confusion with Adder Vipera berus and Slow Worm Anguis fragilis. Such confusion clouds the interpretation of the current distribution map.
The popularity of the Grass Snake as a pet probably accounts for the occasional anomalous records of Grass Snakes well outside the recorded distribution, which also adds to the confusion about their status in our region. For instance the individuals caught in Wark in 1980, Esh Winning in 2009 and the 2007 Grass Snake from Seaton Carew which were all probably escapees. Langton (1989) records that in 1983 he found a market stall in Newcastle upon Tyne which was selling locally-caught Grass Snakes, probably from the Derwent Valley population. A captive Grass Snake probably originally from Gibside was re-released there in 1986. Another, of pet trade origin, was released by a Newcastle University researcher at Lockhaugh in 1988.
The current status of the Grass Snake can be summarised as no recent records for Northumberland, where an investigation of its status is urgently required. In Durham the last record was of two typically coloured Grass Snakes on the Gibside Estate in 2009 (John Grundy, pers. comm., 2012). The Derwent Valley and the Gibside Grass Snakes require a special mention. The first Grass Snake record for the Derwent valley was in 1886 (Fawcett, 1900) with no further records until 1960 at Mereburn (Alan Brown, pers. comm., 1989). There is a subsequent scatter of records along the valley of the Derwent but a long term presence is only recorded on what is now the National Trust’s estate at Gibside. Coult (2012) summarises the history of these snakes concluding that the population exhibits colour forms indicating a possible hybrid population between the native Grass Snake and introduced snakes from Eastern Europe. Snakes recorded at Gibside may show the typical colour form or may have a reduced collar and a pair of pale dorso-lateral stripes as in Grass Snakes found further east than the Po Valley in Italy. No Grass Snakes have been found at Gibside since the 2009 specimens and Durkin (2006) surmises that the population is under threat due to conflict between the requirements of the snakes and the increased numbers of visitors to the estate. Given the increased facility of DNA analysis, if biological material from Gibside can be obtained then genetic provenance of the Gibside snakes should be determined, and in any case survey work at Gibside and along the Derwent Valley in County Durham is urgently required.
It is difficult to draw any conclusion from the records and the history other than that the Grass Snake in Northumberland and Durham is in decline, possibly verging on extinction.
by Terry Coult