Four major categories of food items were determined in the gut content of chironomid larvae collected in the Curonian and Vistula Lagoons in the spring-summer period of 2009-2011. These were detritus (range from 88 to 92% of the gut content, by volume), matter of plant (2-7%) and animal origin (0.2-0.5%), and mineral particles (3-7%). Plant matter comprised pine pollen, conidia of fungi, cyanobacteria, green algae and diatoms. Matter of animal origin consisted of remnants of oligochaetes and rotifers. Food content was more diverse in the larvae inhabiting the Curonian Lagoon. The size of mineral particles in gut contents was significantly higher in C. balatonicus, although the distance between the bases of the maxillas, as a predictor of the size of the particles being eaten, was larger in C. plumosus. The gut content analysis suggested lack of clear food selectivity which potentially may lead to interspecific competition for food. However, the strength of interaction can be substantially weakened by several factors: (1) exceptionally favourable food conditions for benthic chironomids in both highly eutrophic lagoons, (2) the ability to occupy areas differing in salinity, (3) different feeding behaviour and (4) the ability to swallow particles of different size spectra.

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