Recording the insect species of hollow trees, particularly in larger cavities, presents a major methodological challenge. A whole range of endangered saproxylic beetles and other wood-inhabiting species live together in this habitat. In order to conduct preliminary surveys and monitor populations of the hermit beetle (Osmoderma eremita) in Natura 2000 areas designated for nature conservation according to the EU Habitats Directive, a vacuum cleaner has been used for the first time. Sampling of 127 trees with cavities revealed 39 trees in which O. eremita was present and for which submission of a report is mandatory. A total of 35 species was found, including 17 species in the German red data book as well as six species which are classified as relict species of ancient woodland. The method has therefore proved itself to be very appropriate and is now routinely used in southern Germany.