EN
As a result of parasitological necropsies of 28 wild ruminants (8 European bisons, 2 roe deer and 18 red deer) shot in the Bieszczady Mountains, 100% infection by blood sucking nematode Ashworthius sidemi, localised in abomasum, was determined. In most cases there were mass invasions. Infection of wild animals by A. sidemi takes place mainly from June to September. Nematodes from this infection reach sexual maturity not before June of the following year, and from September of the next year begins the process of freeing the wild ruminants from parasites of this generation. Thus, from June to September in wild ruminants in the Bieszczady Mountains two generations of nematodes occur: the previous year one in the form of sexually matured specimens and the current year one in the form of the 4th and 5th stadium larvae and young adults specimens. In winter and spring till June only one generation of nematodes occurs in the host in the form of arrested larvae of the 4th stadium and young adults. Moreover, morfology of eggs, invasive larvae and adult A. sidemi were described. This will help at intra vitam and post mortem diagnosis of this parasitosis. The authors believe that this nematode can occur in cattle and sheep on woodland pastures and meadows in the Bieszczady Mountains.