Anyone who has spent any time scrutinising a bramble bush at this time of year (is it just me then?) will recognise the squiggly trail left by the caterpillar of a Bramble Leaf Miner Moth (Stigmella aurella). The moth lays its egg inside the leaf where the larva hatches and slowly snakes its way through the leaf by eating a tunnel just below the outer skin of the leaf.
As the caterpillar chomps its way through the leaf tissues it inevitably grows, and consequently the tunnel gets bigger and wider. You'll notice inside the tunnel the caterpillar leaves behind a little dark line of what entomologists politely call "frasse" (it's poop), and this shows up well if you hold the mine up to the light (free lightbox here).
Eventually the caterpillar reaches full size and pupates ready to emerge as an adult moth. You can sometimes see a small slit in the largest end of the tunnel where the moth would have escaped. The adult moth has a silvery sheen to its wings and a cream coloured streak running across the middle of them. You could spot one as early as February.