Grass Snake

The grass snake (Natrix natrix), sometimes called the ringed snake or water snake, is a Eurasian semi-aquatic non-venomous colubrid snake. It is often found near water and feeds almost exclusively on amphibians.

Subspecies

Many subspecies are recognized, including:

Natrix natrix helvetica (Lacépède, 1789) was formerly considered as a subspecies, but following a genetic analysis it was recognised in August 2017 as a separate species, Natrix helvetica, the barred grass snake. Four other subspecies were transferred from N. natrix to N. helvetica, becoming N. helvetica cettii, N. helvetica corsa, N. helvetica lanzai and N. helvetica sicula.

The subspecies N. natrix astreptophora, found in the Iberian peninsula, the Pyrenees, and North-Western Africa, has been reclassified as its own species Natrix astreptophora or the Iberian grass snake.

Description

The grass snake is typically dark green or brown in colour with a characteristic yellow or white collar behind the head, earning it the alternative name of 'ringed snake'. Its colouration can range from grey to black; darker colours are more prevalent in colder regions, presumably due to the thermal benefits of dark pigmentation. The underside is whitish with irregular black markings that are a useful field identification feature. It can grow to 1 m (3 ft 3 in) or more in length.

Evolution

Fossils of N. natrix are known to date back to the late Early Pleistocene from the site of Somssich Hill 2 in southern Hungary.

Distribution

The grass snake is widely distributed in mainland Europe, ranging from mid Scandinavia to southern Italy. It is also found in the Middle East and northwestern Africa.

Grass snakes in Britain were previously classified as the subspecies N. n. helvetica but have since been reclassified as the barred grass snake Natrix helvetica. Any records of N. natrix in Britain are now believed to be from imported specimens.

Ecology

Feeding

Grass snakes mainly prey on amphibians, particularly the common toad and the common frog, although they may also occasionally eat ants and larvae. In captivity, grass snakes have been observed accepting earthworms offered by hand, but they never take dead prey. The snake actively searches for prey, often on the edges of the water, using sight and sense of smell (using Jacobson's organ). They consume prey live without using constriction.

Habitat

Grass snakes are strong swimmers and can be found near bodies to fresh water. However, there is evidence that individual snakes often do not always require access to water throughout the entire season.

The preferred habitat appears to be open woodland and "edge" habitats, such as field margins and woodland borders. These areas may offer adequate refuge while still affording ample opportunity for thermoregulation through basking. Pond edges are also favoured and the relatively high likelihood of observing this elusive species in these areas may explain why it is often associated with ponds and water.