The paper summarizes new and literature data on the species composition, trophic relationships, and population dynamics of phyllophagous lepidopterans dominant on woody plants in St. Petersburg and its environs (Russia). Most of these species have concealed larvae (e.g., leaf miners and leaf rollers), and some of them are invasive. The data were accumulated during approximately a hundred years of observations and field collections. Concealed species form the dominant group within the studied complex of phyllophagous moths in St. Petersburg and Leningrad Province (27 species from 13 families). Changes in the composition of dominant pests of the dog rose, bird cherry, elm, poplar, and other woody plants have been recorded. Outbreaks of some species, such as Phyllonorycter salicicolella (Gracillariidae), Archips rosana (Tortricidae), Leucoma salicis, Lymantria monacha, and Orgyia antiqua (Erebidae), were recorded during the XX century but since about 1980 the population density of these species has remained at a very low level. Another group of species, which includes Phyllonorycter populifoliella (Gracillariidae), Batrachedra praeangusta (Batrachedridae), Acleris bergmanniana, and Epinotia abbreviana (Tortricidae), demonstrated a sharp increase in population density in the 1990–2000s, a phenomenon which had not been observed before. The possible causes of such population dynamics are discussed. The dominant species of phyllophagous micro-lepidopterans, including some recent invaders (e.g., Cameraria ohridella and Phyllonorycter issikii, Gracillariidae) and adventive species (e.g., Ph. populifoliella and Ph. acerifoliella, Gracillariidae) pose a serious threat to woody plants in St. Petersburg and Leningrad Province.