Materials and methods. A total of 32 grey and 41 black dice snakes Natrix tessellata from three habitats in the Astrakhan region, caught in 2004, 2005, and 2008, were examined using the method of complete helminthological dissection. The parasitological material was processed using standard methods. Statistical analysis was performed using the Shannon, Jaccard, Sorensen, Palia-Kovnatski dominance indices, and the Mann-Whitney criterion.

Results and discussion. A comparative analysis of the helminth fauna in dice snakes of the grey and black morph was conducted. A total of 21 species of parasitic worms were found in dice snakes examined: Cestoda – 1, Trematoda – 11, Nematoda – 8, Acanthocephala – 1. All these species of helminths were found in grey dice snakes. In black N. tessellata, 18 species of parasites were recorded. Paralepoderma cloacicola, Camallanus lacustris and Centrorhynchus aluconis were found only in grey morph of the dice snake. The analysis of the total helminth infection in dice snakes of different morphs did not reveal any significant differences, as well as pairwise comparison of the infection of reptiles by common parasite species. It was found that the structure and dominance of parasites in the helminth fauna of grey and black N. tessellata differs. Comparison of the helminth fauna of grey and black dice snakes in both qualitative and quantitative terms showed a high degree of similarity. Analysis of the helminth species diversity in dice snakes of different morphs revealed that the diversity of the parasite fauna of grey and black N. tessellata is approximately at the same level. Similar structure of helminths in dice snakes of different colors indicates the similarity of their topical and trophic niches. Relatively high infection of grey dice snakes with helminths is probably due to differences in physiology. It was established that both morphs of N. tessellata take part in the formation of the helminth fauna of the dice snake.