Typically, an adult lays an egg on or in a leaf, and the hatched larva burrows into the tissue. The entire developmental sequence, larval feeding, growth, and sometimes pupation within the leaf, is recorded as a mine until the insect either dies inside, pupates there, or emerges as an adult. Leaf mining has evolved repeatedly and independently in several insect lineages. It is especially well known in many moth families (such as the Gracillariidae and Nepticulidae), but also occurs in beetles (including some weevils and buprestids), sawflies, and leaf-mining flies (Agromyzidae). Mines vary greatly in form: they may be linear, serpentine, blotch-like, or a combination of these types. In some cases, the larva’s frass (fecal material) is preserved within the mine, forming characteristic patterns that help identify the producer. Because many leaf miners are highly host-specific—often restricted to particular plant families, genera, or even species—mining represents one of the most specialized and intimate plant–insect interactions. In modern ecosystems, mine shape, frass pattern, and host association can sometimes allow identification of the insect to family, genus, or even species, and similar principles are applied in fossil studies.