|A plump Natrix helvetica, showing barred stripes and no collar.|
|Natrix natrix (type species)|
It is one of only three snakes to occur in Great Britain, the others being the adder and the smooth snake. It is found in lowland areas of England and Wales. It is almost absent from Scotland and is not found in Ireland, which has no native snakes.
It is now known that there are two species in Britain. One is Natrix natrix, the original type species. It is olive green with a yellow collar or black-and-white collar. The other is the barred grass snake, Natrix helvetica, which is grey-brown with black stripes and no collar. The difference had been noticed, but was regarded as a difference between subspecies. Both forms are protected by law: it is an offence to harm them.