Apple Leaf Miner Lyonetia clerkella

The Apple Leaf Miner, like other leaf miners, is a small caterpillar that develops inside the leaf of its host plant and leaves a brown trail showing its route. The adult is a small white moth, prevalent across most of temperate Eurasia and common in Britain. The female lays some 50 eggs, one in the underside of each leaf of an apple or another fruit tree. The glassy green necklace of a caterpillar is some 5mm long when it emerges from the leaf to pupate, leaving the tell-tale trail of brown.