Chironomidae larvae may represent more than 70% of total Arthropoda numbers in hypersaline waters. Crimea, the largest peninsula of the Black Sea, has more than 50 hypersaline water bodies of marine and continental origin. Chironomidae larvae are common components of their ecosystems, but they still are poorly understood. This paper summarizes the results of a long-term study (2007-2016) of chironomids in Crimean hypersaline waters. More than 400 samples from 38 water bodies were used for analysis. The maximum salinity of water bodies containing Сhironomidae larvae was between 320 and 340 g/L. At first it was shown that Baeotendipes noctivagus (Kieffer, 1911) is the most halotolerant chironomid species in the world. Frequency of larvae occurrence varied and was negatively dependent on salinity. Four chironomid species were found: B. noctivagus, Cricotopus gr. cylindraceus (Kieffer, 1908), Tanytarsus gr. mendax Kieffer, 1925 and Paratanytarsus sp. Ceratopogonidae larvae were also found twice, at salinities of 150 and 270 g/L. B. noctivagus was the most common species, which occurred in 81% of samples with chironomids. Abundance of larvae fluctuated widely and reached high numbers: in planktonto 8 thousand/m 3 , in floating green algae matsup to 3 thousand/m 2 , and in benthosup to 9 thousand/m 2. Nonlinear dependence of chironomid abundance from salinity was observed; maximum abundance was at salinity levels of between 150 and 170 g/L. The average weight of larvae of 0.05-1.50 mm in length varied little in the samples; however, larvae of greater length had a significantly different average weight. Larvae of 8 mm in the samples had the average actual weight, which ranged from 0.750 to 2.203 mg.

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Measuring the linear characteristics of chironomid larvae is easier and faster than measuring their mass. The relationships between them are approximated by parabolic equations. Generalized equations are provided for all chironomid larvae. However, these relations vary in different water bodies. Measurements of 1424 chironomid larvae representing several species were taken in Crimean waters with salinity ranging from 0 to 280 PSU. There was a high correlation between three traits. In the case of Baeotendipes noctivagus and Cricotopus gr. sylvestris, dimorphism was found in the “head capsule length– width” relationship. Salinity affects the head capsule. The exponent “b” varied from 1.43 to 3.06 in the “body length-mass” equation for B. noctivagus, and from 1.943 to 2.592 for C. gr. sylvestris. It is inappropriate to use only one coefficient “b” for all chironomid larvae. In B. noctivagus and Paratanytarsus confuses, the mass of one-size larvae decreased with increasing salinity. Salinity is not the only factor affecting the size and mass of chironomid larvae.

Salinity is one of the most important factors in aquatic ecosystems, but its filtering role in the Diptera community species composition is still poorly studied. This issue was studied in the diverse Crimean water bodies. A total of 425 samples were collected from freshwater to hypersaline waters. In 73% of the 425 samples examined, representatives of Diptera were found; their larvae and pupae belonged to seven families. Сhironomid species composition was analyzed in 47 samples. The most common were Chironomidae, which were in 94% of samples with Diptera, Ceratopoganidae were in 8% of samples, Ephydridae were in 5% of samples, Simuliidae were in 4% of samples, Culicidae and Chaoboridae were in 4% of samples, and Syrphidae was in only one sample. A total of 14 Chironomidae genera and 21 species and forms were found; 9 of them are new for Crimea. Reduction of the dominance variants in the community, as well as the number of chironomid species, with increasing salinity may indicate an increase in the filtering role of salinity in the Diptera community species composition that is still poorly studied.