Grass snakes mate in the spring, usually around April and unlike the adders, which give birth to live young, they lay eggs.
The female lays the eggs around June/July and they hatch in September as the fully developed young cut their way out of the eggs by using a specially developed egg tooth. This tooth is on the top of their mouth, but is lost soon after hatching.
The mature female finds a suitable place to lay her eggs, usually in a compost heap where she can be sure that they will be protected from the elements, predators and with a temperature ranging between 21 & 28 oC.
Grass snake eggs. You can see where the young snakes have cut their way through the egg, using their egg tooth.