Just something to share with you: we have a big compost heap, one section of which is maturing under a layer of old carpet. In warm weather we get slow worms basking under the carpet, and occasionally a grass snake. Then one day I saw a fat frog, about two inches long, sitting near the slow worms. The next time we looked, there was a small grass snake too, with the frog's head in its mouth! The frog was wriggling, and as we watched it gave a big kick and freed itself. We haven't seen either the frog or the snake since, but the slow worms are still there.
Do grass snakes eat slow worms, I wonder?