The ticks are highly specialized hematophages that are capable to transmit over 10 types of transmissible diseases to animals and humans, in particular: borreliosis, piroplasmosis, anaplasmosis, babesiosis, listeriosis, brucellosis, and others. The deterioration of the acarological situation in Ukraine, the increase of contacts between man and domestic animals with ticks, the existence of natural focus of tick-borne infections cause the large interest in pincers mono infections and the ways of their prevention. Endemic focuses of tick borreliosis were found in 57 settlements of 14 districts and in the city of Ternopil.

The structure of 124 females and 198 nymphs of ticks as Ixodes ricinus (Ir), as well as 58 females and 25 males of the ticks as Dermacentor reticulatus (Dr) were investigated.

As a result of the morphological analysis of individuals of the Ir, regularities in the ratio of total body length to the width of the abdomen were found at different degrees of saturation: unsaturated, partially saturated, saturated, very saturated and maximally saturated. So, for example, in females there is a correlation: 1:0.56; 1:0.59; 1:0.53; 1:0.6; 1:0.7, respectively. In the nymph, the ratio is as follows: 1:0.56; 1:0.56; 1:0.58; 1:0.6; 1:0.58.

Thus, in the genus of Ir not only adult ticks, but also nymphs and even larvae are ectoparasites. Females of ticks are more carriers of the Borrelia burgdorferi senso lato complex, and the nymphs are A. phagocytophilum and B. miyamotoi. Larvae can be ectoparasites of humans and tolerate infectious agents, in particular, A. phagocytophilum. Males of the genus Dr can be feed on the human body and transmit the pathogens of anaplasmosis.