Leaf miners are hard at work, excavating tunnels in the tissue between the upper and lower layers of cuticle. They're chewing their way through the leaves, stuffing their little faces with plant cells or tapping the sap from the veins until they're ready to pupate. That's the life of a larval insect: eat, poo, grow. Oh, and avoid predators, of course. And people with cameras.
Many types of insects have larvae that mine leaves. I'm not sure what these are — beetles, flies, wasps or moths. I might stick a plastic bag around one of the leaves to see what emerges. Because most of these insects have short life cycles, it shouldn't be too long before they pupate and metamorphose into the adult stage. Unless they've been got at by parasitoid wasps, that is.
Leaf miners are used for biological control of some weed species. The herringbone leaf miner fly (Ophiomyia camarae) and a couple of beetle species (Uroplanta girardi, Octotoma scabripennis) have been brought in from South and Central America to give invasive lantana (Lantana camara) a hard time. A species of leaf mining moth (Dialectica scalariella) feeds on Paterson's curse (Echium plantagineum). In these cases, the insects don't kill the target plant but slow down its growth and reduce seed production. The leaf miners in my garden have had no noticeable effect on the weeds.
