Artificially-perforated holes in stems of small hogweed (Heracleum sphondylium L.) mimic ecosystem engineering by the parsnip webworm (Depressaria radiella Goeze)

We conducted a field experiment to determine if artificial holes perforated into stem compartments of <em>Heracleum sphondylium</em> mimic the natural situation with <em>Depressaria radiella</em>. At five locations near the city of Leiden, the Netherlands, <em>H. sphondylium </em>plants were exposed to different treatments: a single hole perforated in the first, second or third stem compartment, or in all three compartments. After three weeks, arthropod numbers were counted inside and around hogweed stems.