<p>Insect hotels are widely promoted to support cavity-nesting bees and wasps, but their effectiveness varies with substrate design and surrounding habitat. We surveyed nesting Hymenoptera at 90 insect hotels across Central Europe. Across 73,259 nesting cavities representing multiple artificial substrates, 11,600 contained nests. We identified 110 bee and wasp species, including 16 Red-Listed taxa. Nesting activity depended strongly on cavity structure: reed stems were consistently used and were often moderately to highly occupied, whereas large-diameter stems and other wide-hollow structures were rarely used. Low occupancy in some reed-rich hotels reflected poor habitat conditions rather than unsuitable reed. Habitat quality was a major predictor of nesting success: hotels in semi-natural habitats and well-structured urban green spaces had higher relative occupancy than those in degraded urban surroundings. Orientation and vegetation openness interacted with habitat quality, indicating that no single placement trait predicts performance in isolation. Insect hotels can support diverse assemblages of cavity-nesting Hymenoptera when paired with suitable habitat context and broader habitat management. Importantly, thermophilous taxa frequently occupied cooler, moister microhabitats, consistent with microrefugial responses to global warming.</p>