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Predatory invertebrates play a significant role in the organisation of aquatic communities. However, their ecology is poorly known even for many common taxa. We examined the meso-habitat use and aspects of movement activity of two common predatory water bug species Ilyocoris cimicoides (L., 1758) and Nepa cinerea L., 1758 under field and laboratory conditions in order to assess the effect of the patchiness on habitat choice. Ilyocoris cimicoides preferred open habitats, rich in submerged vegetation, without submerged terrestrial materials. Shaded habitats such as under trees, with moderately dense vegetation and submerged branches, were favoured by N. cinerea. Both laboratory and field data indicated differences in the short-term and similarity in the long-term movement behaviour of the two species. In the short-term, I. cimicoides moved frequently, while N. cinerea moved rarely, but the distance visited over the course of a longer time span is comparable.

Detailed faunistic data originating from four sampling series of aquatic Heteroptera (Nepomorpha) in the Lake Balaton (the largest shallow lake of Central Europe) between 1928 and 2002 were analysed. A comparative analysis confirmed that the aquatic bug fauna of this great lake can be established with suitable accuracy if it is sampled by different but devoted collectors. So far 26 species of aquatic bugs have been reported from here. The fauna changed considerably during the seven decades. Species lists of the four basins of the lake established during the four sampling periods show characteristic differences. Not only the frequency of four Micronecta species (Micronecta griseola, M. pusilla, M. scholzi, M. minutissima) changed characteristically but there has been a distinct change in the ratio of rare species too. Rare species were present in significantly higher proportion in the period 1928–1930 than in any of the later samplings between 1984 and 2002. All these changes run parallel with the directio...