The paper describes impacts of the main ecological factors on the development of horse fly populations in the alluvial floodplains of the Danube River in the Pannonian plain. The study has been conducted from 2004.2009 in the four, water dependent, succession stages of alluvial forest communities of Kopacki rit wetlands. In total more than 23 000 adult horse flies of 22 species were collected by canopy traps that were placed annually during the flight season from May-September. The most abundant species during the study period were: Tabanus bromius with 47%, T. sudeticus with 17% and Haematopota pluvialis with 11%, respectively. Correlation analysis has confirmed the influence of the deviations from long-term average values in the temperature, precipitation and flood duration on the numbers of adult horse flies during the following year. A significant positive correlation has been found between spring and autumn precipitation and rainy seasons yielded more horse fly individuals the following year. A significant negative correlation has been found between the higher temperatures during summer, autumn and spring and the number of adults in the following year. The impact of the seasonal divergence from long-term average values in temperature, precipitation and flood on different species was not straightforward and different species have shown diverse correlation responses, either positive or negative.