Abstract: During four years of sampling by canopy traps with fermenting baits, adults of the Quedius dilatatus rove beetle were collected in large quantities together with the Vespa crabro hornet across several regions in Central European Russia. Contrary to previous reports which stemmed from collecting methods inadequate for this ‘rare’ inquiline of the European hornet Vespa crabro, Q.dilatatus is found to be a common and widespread beetle. Moreover, the maximum numbers of beetles were found in the period between the first (spring) and second (summer) peaks of the hornet abundance, i.e. at the early stages of the hornet nests’ growth to their peaks. A similar pattern was revealed by the same type of sampling during one year within a smaller area of the Mordovia State Nature Reserve, albeit with variation determined by the type of sampled forest. Apparently, such adjustment of the life cycle of the inquiline beetle to that of its host is a compromise between the possibility for efficient search of the hornet nests by beetles using olfactory stimuli, and the availability of a sufficient time period needed for the development of the beetle larvae. The latter, as shown by earlier studies, prey on fly larvae in the debris around active nests.