Giant hogweed, Heracleum mantegazzianum (Apiaceae), was introduced from the Caucasus into Western Europe more than 150 years ago and later became all invasive weed which created major problems for European authorities. Phytophagous insects were collected in the native range of the giant hogweed (Caucasus) and were compared to those found oil plants in the invaded parts of Europe. The list of herbivores was compiled from surveys of 27 localities in nine countries during two seasons. In addition, literature records for herbivores were analysed for a total of 16 Heracleum species. We recorded a total of 265 herbivorous insects on Heracleum species and we analysed them to describe the herbivore assemblages, locate vacant niches, and identify the most host-specific herbivores oil H. mantegazzianum. When combining our investigations with similar studies of herbivores on other invasive weeds, all studies show a higher proportion of specialist herbivores in the native habitats compared to the invaded areas, supporting the "enemy release hypothesis" (ERH). When analysing the relative size of the niches (measured as plant organ biomass), we found less herbivore species per biomass oil the stem and roots, and more on the leaves (Fig. 5). Most herbivores were polyphagous generalists, some were found to be oligophagous (feeding within the same family of host plants) and a few had only Heracleum species as host plants (monophagous). None were known to feed exclusively oil H. mantegazzianum. The oligophagous herbivores were restricted to a few taxonomic groups, especially within the Hemiptera, and were particularly abundant oil this weed.