Grass snakes

Couleuvre helvétique (previously Couleuvre à collier)  
Natrix helvetica

Couleuvre astreptophore 
Natrix astreptophora

In France there are two species of Grass snake

and these are Natrix helvetica, (sometimes called the Swiss Grass snake), which is present everywhere in France and Natrix astreptophora, the Iberian Grass snake, which is found in Ariége, Aude and Pyrénées-Orientales. These are distinct species that are genetically different - not sub species.

Grass snakes display a large degree of variation

in both body colouration and markings with shades of grey/green with darker splashes or bands being most common, but some individuals can be all dark grey or black.

They get their previous name in French from the characteristic collar which is formed by two half moon bands at the rear of its head, these can be yellow, white, red or orange in colour, although in some individuals this can be absent. 

Females can grow with age into very large snakes, anything up to 2 metres, males possibly 80cm with an average of 60cm.

They can be found all over France in all types of habitat

be that woodlands or open spaces, but with a preference for areas where water is present to some degree. They are quite happy to live alongside Asp vipers. Their preferred diet is frogs, lizards, newts, small fish including their larva and eggs; they will also prey on insects, baby birds, small mammals, voles etc. As can be seen in the pictures they have the ability to swallow quite large prey whole.
Grass snake eating a Salamander
Grass snake eating goldfish, France
Natrix astreptophora - Iberian Grass snake

They have no venom fangs

 however as with all non venomous snakes they do have tiny teeth but these are completely harmless and only used for gripping prey.  They can bluff convincingly by hissing loudly, puffing up their heads and striking it hard against the perceived threat but rarely causing any harm, in fact their only real defence is to emit an unpleasant odour from their anal glands. Their last resort if cornered is to “play dead” often laying on their backs with their head twisted or turned back, mouth open with tongue hanging out. These methods may work in their favour in certain instances but not against a serious predator!
Grass snake mouth showing "teeth"
Grass snake "playing dead"

They are superb swimmers and can often be observed in lakes, ponds and rivers with their head held straight up out of the water; diving and swimming under water is another strong point being able to hold their breath for a good 20 minutes. They can also be seen from time to time in trees sunning themselves on low branches or in a trunk fork.

Hibernation is another variable

and can take place from September/October or even November until March/April under a compost pile or other deep decomposing vegetal matter, a pile of rocks or in a rock fissure.

Coupling takes place in two distinct periods

 the first just after coming out of hibernation and after the first “moult or skin shedding” (sloughing) in March/April and the other in the autumn just prior to hibernation. The period of coupling can bring together a large group of grass snakes in the same place - more males than females. Fertilisation takes place internally and it seems that females are able to “keep the male sperm” and decide according to conditions whether or not to fertilise themselves!  Up to 50 eggs are laid always around the month of July inside a heap of compost, under a deep pile of leaves or in the base of a rotting tree stump. The young hatch after 4 to 8 weeks and are 15/20 cm in length and having shed their skin in the first few days may sometimes go directly into hibernation.
In localised decline, principally due to habitat loss and fragmentation.