The Hellebore Leaf Miner is a tiny fly, belonging to the taxonomic group that holds flies with leaf-mining larvae. Leaf-mining insects are usually small, and it's the larvae that cause the most the damage. They do this by tunnelling through the leaf tissue, eating the contents as they do. Mining activity can be a helpful clue to help you identify what's eating your plants. As well, the species of plant infested can be a telltale sign. For example, these miners will only infest Helleborus foetidus. Dull brown blotches paired with sinuous light brown trails should be evident across foliage.