CSU Extension Leafminers are insects that develop and live within the leaves of plants. Typically, the leaves are injured by the insect feeding on the soft interior tissues so that only the papery-thin covering of the exterior leaf surfaces remain. Serpentine leafminers make mines that zig-zag through the leaf and gradually enlarge from beginning to end. Blotch leafminers make large indistinctly shaped mines. Blotch leafminer injury often is mistaken for leaf splot diseases.
Many different insects are leafminers, including certain flies, wasps, moths and beetles.
For some leafminers, the pupal stage also takes place within the leaf. More commonly, the insect larva, after it completes feeding, cuts a hole in the mined leaf and drops to the ground to pupate. Adults move about freely to mate, lay eggs and feed. Leafminer eggs are laid on the leaves or are inserted just under the leaf surface. Leafminers rarely are abundant enough to be injurious to the plants they infest.