The study presents the results of investigations on changes in groups of Noctuidae (Lepidoptera) of xerothermic rock sward ecosystems in the Pieniny caused by storage reservoirs in the Pieniny foothills, operating for over a decade now. A comparative analysis, taking into consideration exclusive characteristic species and indexes of similarity between groups investigated 40 years ago and at present (in 2003–06) at the same sites clearly shows that changes in the Noctuidae fauna are regressive in character only in the immediate vicinity of the water reservoirs and as the distance from a reservoir increases, the negative effect decreases until it disappears completely. Considerable regressive changes may be observed in the following spots: Zielone Skałki (index of similarity), Niedzica Biała Skała (15.74) or Czorsztyn Hill (22.86). In contrast, at present these changes are not observed on Zamczysko (index of similarity 55.55) or Macelowa Góra (53.3).