Serpentine Leaf Miner: the trail of the serpent -

There are some small species of moth that lay an egg in the fabric of a leaf so that when the egg hatches the larva can mine its way through the leaf as a food source. This mining process can produce a range of different effects that show on the leaf, each shape generally unique to each species.

This one looks a bit like a snake or serpent; it starts narrow but as the larva grows so the width of the stream produced grows and eventually it stops at the point the where the larva escapes and pupates. The larva actually over winters in its mine.

The particular serpent shape is made by one of the most common of the species that do this and, not surprisingly, it is therefore called the serpentine leaf miner (Stigmella aurella). This species has a preference for bramble leaves and so this is probably the mine of that species. The moth itself is very small and looks like a midge!